NECTAR SECRETION AND HOW IT AFFECTS THE ACTiVlTY 0F HONEY BEES N THE POLLINATION OF HYBRID PiCKLlNGCUCUMBERS, CUCUMIS SATIVUS L. . Thesis for the Degree of M. S. MiCHlGAN STATE umvERsmI - f CLARENCE: H. cow'soN 1973 _ mum; um um gm 1| mu m min um um ' 3 9751 LIB R A R Y ' Michigan Sta EC J University a" ‘0 .un'lu- " WWWi Mfw‘w’ .mw it“? HE”! mi)! 33%? 4-,? 2/ ‘gé‘amfé- a QHWZQ W5 Ilia fi‘ JAN 1 2 2004 052.: o? ABSTRACT NECTAR SECRETION AND HOW IT AFFECTS THE ACTIVITY OF HONEY BEES IN THE POLLINATION 0F HYBRID PICKLING CUCUMBERS, CUCUMIS SATIVUS L. BY Clarence H. Collison Nectar secretion in both staminate and pistillate flowers of pickling cucumber was the primary attractant to honey bees. Few bees collected cucumber pollen. All cultivars tested produced a quantity and quality of nectar that was attractive to bees. The pistillate flower nectary is cup-shaped, surrounding the base of the style, whereas the staminate flower nectary is typically a three-lobed button on the floor of the receptacle, with a few being four-lobed. The pistillate flower nectary was l.6-l.9 times wider,e had approximately twice the secreting surface and secreted 1.5-2.3 times more nectar than the staminate flower nectary. The epidermal layer of the nectary contained stomate-like pores that appeared to open and close with environmental changes. Cucumbers basically have a one day secretion cycle with maximum production on the day of anthesis. Nectaries became moist at 16° C and measurable amounts of nectar were obtained at 2lo C. Cucumber flowers have a range of nectar production from zero to over 30 ul, with l32 - 60% sugar content or O to 12.33 mg of sugar. The sugar concentration was Clarence H. Collison drastically reduced during the night after anthesis by sugar reabsorp- tion. Positive correlations were found between nectary width and petal diameter, volume of nectar, total weight of sugar present and ovary length but not sugar concentration. ,The nectar of staminate flowers had a higher sugar concentration than that of pistillate flowers but both had approximately equal weights of sugar. Bees spent twice as long on pistillate as on staminate flowers since the length of the visit is determined by the amount of the nectar present. Nectar replacement after removal occurred within five minutes with a decrease in sugar concentration and total weight of sugar present. Multiple visitation did not stimulate nectar production. A 40% differ- ence in sugar concentration was found between nectar sampled from bee excluded flowers and nectar removed from the honey stomachs of bees working cucumbers. There tended to be slight increases in flower size, nectary size and volume of nectar in flowers produced further down the vine from the base. Lateral vine flowers produced more nectar with a higher weight of sugar than main vine flowers. Only morning pollinations affected nectar secretion. After fertilization, nectar secretion appeared to cease. Two different gas chromatography columns were needed to analyze nectar for sugar content. The nectar samples changed quantitatively within 2A hours after the silylation reagent was added. Cucumber nectar was sucrose dominant (60.5%) with fructose (25.l%) predominating over glucose (IA.A%). Two unknowns were found. Clarence H. Collison Cucumber nectar would rate moderately attractive compared with other major nectar sources, but because of a relatively small number of flowers per acre, it cannot be rated as an important honey plant. These studies indicate that important factors of attractiveness of a crop to bees could be readily monitored during a plant breeding program. NECTAR SECRETION AND HOW IT AFFECTS THE ACTIVITY OF HONEY BEES IN THE POLLINATION OF HYBRID PICKLING CUCUMBERS, CUCUMIS SATIVUS L. By Clarence H. Collison A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Entomology I973‘ ACKNOWLEDGMENTS I am indeed very grateful to Dr. E. C. Martin for his guidance, encouragement, patience and support during the past four years which were needed to complete this work. Even while he was on sabbatical and on other assignments he always found time to supply needed direction for the project. Thanks are extended to Dr. R. w. Shuel of the University of Guelph, Guelph, Ontario, Canada for instruction in methodology of nectar secretion studies. i am grateful to USDA Agricultural Research Service, Entomology Research Division, Apicultural Research Branch for financial and advisory support under a Cooperative Agreement arrangement. In particular, I wish to thank Mr. S. E. McGregor and Dr. M. D. Levin of the Apiculture Research Branch, USDA for suggestions and ideas. I wish to thank those individuals who have served on my guidance committee, Dr. Roger H00pingarner, Dr. Roland Fischer, Dr. Larry Baker and Dr. Stanley Wellso. Dr. H00pingarner is thanked for use of his gas liquid chromatograph and the many hours of instruction in its use and Dr. Baker for supplying seed and access to his plots. Thanks are extended to Dr. Gordon Guyer, chairman of the Entomology Department for providing an office, field plots and greenhouse space. I MKMJId also like to thank Dr. Haynes of the Entomology Department for the use of cages, camera and access to calculators. Special thanks to Dr. Lawrence Connor, Ohio State University for his assistance and advice during the research and writing of this thesis. Appreciation is extended to all summer help and eSpecially to Larry Olsen, Dan Young, Dan Collar and Dale Maki. Thanks are also extended to Abby Edwards, Kathy Merrick and Steve Parise for many hours of typing. I am most deeply grateful to my wife Sally and son Craig for the sacrifices they have had to make during this project. Thanks to my wife for all of her help during the first summer, as well as moral support and proof reading while she has been at home. Finally I thank our families and friends who have offered their support. TABLE OF CONTENTS L ' ST OF TABLES O O O O O '0 O O O O O O O O 0 LIST OF FIGURES . . . . . . . . . . . . . . . INTRODUCTION . . . . . . . '. . . . . . . . . Chapter '0' FLOWER AND NECTARY ANATOMY AS RELATED TO NECTAR SECRETION O O O O O O O O O O O O O The Cucumber Nectary . . . . . . . . Materials and Methods . . . . . . . Results and Discussion . Proportion of Three and Four-Lobed Nectaries _ in Staminate Flowers . Materials and Methods . Results and Discussion Materials and Methods . Results and Discussion . . . . . . . The Nectary as Related to Floral Development . The Vascular Tissue of the Nectary .. . . . . The Procedure Used to Remove Nectar from Staminate and Pistillate Cucumber Flowers ; . . . . Nectary Size and Nectar Secretion . . . . Materials and Methods .’ . . . . . . . Results . . . . . . . . . . . . . Discussion . . . . . . . . . . . . o o o o e 1". o o O C 3 O. Nectar Secretion of Different Aged Flowers Materials and Methods . . . . . . Results and Discussion . . . . . . The Commencement of Nectar Secretion . Materials and Methods . . .- . . . . . Results and Discussion . . . . . . . . A Comparison of Nectar Secretion in Staminate and Pistillate Flowers . . . . . . . . . . Page vii ‘xi Chapter Page Materials and Methods I . . . . . . . . . . 53 Results . . . . . . . . . . . . 53 Materials and Methods II . . . . . . . . . . 5A Results . . . . . . . . . . . . . . . 5A Discussion . . . . . . . . . 56 Nectar Secretion During the Night . . . . . . . 60 Materials and Methods . . . . . . . . . . . 60 Results . . . . . . . . . . . . . . . 6i Discussion . . . . . . . . 62 Comparison of Nectar Secretion In Different Cucumber Cultivars . . . . . . . . . . . . . 65 Materials and Methods . . . . . . . . . . . 65 Results . . . . . . . . . . . . . . . 66 Discussion . . . . . . . 72 The Influence of Flower Position on Nectar Secretion . . . . . . . . . . . . . 73 Materials and Methods . . . . . . . . . . . 73 Results . . . . . . . . . . . . . . . 7A Discussion . . . . . . . . . . . . . . 82 III. THE NECTAR SECRETION CYCLE AND HOW IT IS AFFECTED BY HONEY BEE VISITS AND THE PROCESS OF FERTILIZATION . . 85 Nectar Removal by the Honey Bee . . . . . . . 86 Materials and Methods . . . . . . . . . . . 87 Results . . . . . . . . . . . . . . . 87 Discussion . . . . . . . 87 .The Rate of Nectar Replacement after Removal . . . 89 Materials and Methods I . . . . . . . . . . 89 Results . . . . . . . . . . . . . . . 90 Discussion . . . . . . . . . . . . 93 Materials and Methods II . . . . . . . . . . 93 Results . . . . . . . . . . . 9A Materials and Methods III . . . . . . . . . 94 Results . . . . . . . . . . . . . . . 9A Discussion . . . . . . . . 9A The Concentration of Cucumber Nectar at :the Time of Collection by the Bee Throughout the Day . . . . 96 Materials and Methods . . . . . . . . . . . 97 Results . . . . . . . . . . . . . . . 98 Discussion . . . . . . . 98 The Effect of Pollination on Nectar Secretion . . . IOO Materials and Methods . . . .. . . . . . . . 100 Results . . . . . . . . . . . . . . . l03 Discussion . . . . . . . . . . . . . . Il3 Chapter Comparison of the Attractiveness of Staminate and Pistillate Cucumber Flowers to the Honey Bee Materials and Methods . . . ReSUIts O O O O O O 0 Discussion . . . . . . IV. THE CHEMICAL COMPOSITION OF CUCUMBER NECTAR Test of Gas Liquid-Chromatography for Nectar Analysis . . .‘ . . Materials and Methods .~ Results . . . . . Discussion . . . SUMMARY AND CONCLUSIONS . . . . . LIST OF REFERENCES vi Page IIA I15 IIS Il6 II9 I20 l2] IZA I32 137 IAS Table IO. 11. 12. 13. LIST OF TABLES Page Comparison of the number of three and four-lobed nectaries present in staminate flowers of various cucumber cultivars . . . . . . . . . . . . . l8 The average flower diameter and nectary width of pistillate and staminate flowers for several cucumber CUItIvars O O O O O O O O O O O O O O O O 29 Percent of the nectaries from staminate and pistillate flowers found within each size group . . . . . . . 33 Correlation of nectary size with petal size . . . . . 3A Correlation of nectary size with volume of nectar prOduced e o o o o e o o e e e o o e o o 35 Correlation of nectary size with sugar concentration Of nectar O O O O O O O O O O O O O O O O 35 Correlation of nectary size with total weight of sugar in the nectar e o o o o e o e o b o o e o o 36 Percent of the pistillate flower nectaries found within each size group. (l969) . . . . . . . . . . . 36 The correlation of nectary size with petal size, volume of nectar, sugar concentration and total weight of sugar in the nectar. (I968B) . . . . . . . . . 37 Correlation of nectary size with volume of nectar, sugar concentration and total weight of sugar in the nectar. (l969) . . . . . . . . . . . . . . 38 Correlation of nectary size with flower size and ovary length. (1969) . . . . . . . . . . .° . Al Average petal size and ovary length of SMR 58 and Spartan Progress. (l969) . . . . . . . . . . . Al The average dimensions of the pistillate and staminate flower nectaries of several cucumber cultivars as measured by an optical miCrometer . . . . . . . . Al vii Table IA. I5. 16. 17. 18. 19. 20. 21. , 22. 23. 24. 25. Page The comparison of nectar secretion In different.aged cucumber f] omrs O O O O O O O O O O O O O O ”8 The percent of the pistillate flowers producing nectar throughout the first day of bloom and the average volume of nectar, sugar concentration and total weight of sugar present . . . . . . . . . 55 The percent of the staminate flowers producing nectar throughout the first day of bloom and the average volume of nectar, sugar concentration and total weight of sugar present I O O O O O O O O I O O O O O O O 57 The range of values within the cycle of nectar secretion for pistillate and staminate cucumber flowers throughout the fII’St day Of bIOOIll e e e o I e e e o e o e' a 58 The average volume of nectar, sugar concentration and total weight of sugar which remains In staminate and pistillate cucumber flowers during the night . . . . 63 The average volume, sugar concentration and total weight of sugar present In nectar from flowers of eight different seed lots of various cultivars (2nd planting) . 67 The average volume of nectar produced by staminate and pistillate flowers from eight different seed lots of various cultivars . . . . . . . . . . . . . '69 The average sugar concentration of nectar produced by staminate and pistillate flowers from eight different seed lots of various cultivars . . . . . . . . . 70 The average weight of sugar found In the nectar produced by the staminate and pistillate flowers from eight different seed lots of various cultivars . . . . . . 71 A comparison of the average volume of nectar, sugar con- centration and total weight of sugar produced by stamin- ate and pistillate cucumber flowers located on main and lateral vines. (1968A) . . . . . . . . . . . 76 Effect of node position on flower size, nectary size and nectar secretion of staminate cucumber flowers . . . . 78 Effect of node position on flower size and-nectar secre- tion of pistillate cucumber flowers . . . . . . . 79 viii Table Page 26. Comparison of main and lateral vine flower position on nectar secretion of eight different seed lots. (I968C) . 80 27. Comparison of staminate and pistillate cucumber flowers located on the main and lateral vines of eight different seed lots. (l968C) . . . . . . . . . . . . . BI 28. The amount of nectar removed from a pistillate flower in one VHSIt O O O O C O O C O O O O O C O O 88 29. The average volume of nectar replaced in pistillate cucumber flowers after removal at hourly intervals . . 92 30. The average sugar concentration of nectar replaced in pistillate cucumber flowers after removal at hourly intervals . . . . . . . . . . . . . . . . 92 31. The average weight of sugar in nectar replaced by pistillate cucumber flowers after removal at hourly IHEBFVBI S o o o o e o e o o e o e o e o o 95 32. The average volume of nectar, sugar concentration and total weight of sugar In the nectar replaced after removal at l5 minute intervals . . . . . . . . . 95 33. The average volume of nectar, sugar concentration and total weight of sugar in the nectar replaced after removal at 5 minute intervals . . . . . . . . . 95 3A. Concentration of cucumber nectar in the honey stomachs of honey bees throughout the day . . '. . . . . . lOI 3S. Concentration of cucumber nectar in the honey stomachs of honey bees after removal of low values . . . . . 101 .36. The percentage of the flowers producing nectar throughout _ the day after the nectar is removed and the flower pollinated. (l968A) . . . . . . . . . . . . 107 137. The volume of nectar, sugar concentration and total weight of sugar produced after the nectar was removed and flowers pollinated in the greenhouse . . . . . . 107 38. The average weight of sugar produced after the nectar was removed and flowers pollinated with zero values included . . . . . . . . . . . . . . . . 107 ix Table Page 39. The influence of flower position on nectar secretion In flowers where the nectar supply ls removed and the flower pollinated . . . . . . . . . .' . . . 109 A0. The effect of pollination on nectar secretion. (l968B) . 109 A1. The effect of pollination on nectar secretion for the cultivars MSU 356 and Piccadilly . . . . . . . . 110 A2. Nectar secretion In cucumber flowers 2A hours after pollination, comparing successful pollination (fruit formed) with unsuccessful pollination (no fruit formed) . 110 A3. The effect of pollination on the percentage of flowers . producing nectar . . . . . . . . . . . . . . 112 AA. The effect of pollination on nectar secretion 16 hours later. (1969) . . . . . . . . . . . . . . 112 A5. Comparison of the pollinated flowers with regard to fruit development when the flower was removed and nectar sampled 16 hours after pollination . . . . . 112 A6. Comparison of the time spent on pistillate and stamin- ate cucumber flowers by honey bees . . . . . . . . 118 A7. Cucumber nectar samples analyzed by gas liquid chromatography . . . . . . . . . . . . . . 123 A8. The composition of cucumber nectar on the day of SIIYIatIOn o o' o ‘o o e o o o o e o o e o o '27 A9. Percentages of sugars in nectar from staminate and pistillate cucumber flowers . . . . . . . . . . 128 50. Percentage of sugars In nectar from various cucumber cultivars .- . . . . . . . . . . . . . . . 128 .51. Stability of silylated nectar samples and standards . . 130 52. Comparison-of methods for transporting nectar samples, to the laboratory . . . . . . . . . . . . . . 131 IO. 11. 12. LIST OF FIGURES Nectary of the staminate flower as seen through a dissecting microscope . . . . . . . . . . . . . . . . View of the staminate flower nectary and stamens . . . Nectary of the staminate flower as seen by a scanning electron microscope. 20x . . . . . . . . . . Four-lobed nectary of the staminate flower as seen by a scanning electron microscope. 20x . . . . Scanning electron photomicrograph of the three- lobed nectary of the staminate flower showing the stomate-Iike pores of the epidermis. 80x . . . Scanning electron photomicrograph of the three- lobed nectary of the staminate flower showing the stomate-like pores of the epidermis open. 800x . . Scanning electron photomicrograph of the four- lobed nectary of the staminate flower showing the closing of stomate-like pores of the epidermis. 800x . . . . . . . . . . . . . . . . . . . Cup-shaped nectary of the pistillate flower with stigma and style removed as seen through a dissecting microscope . . . . . . . . . . . . ._. . . . Cup-shaped nectary of the pistillate flower with droplets of nectar on the nectary tissue . . . . . . . Pistillate flower with corolla and calyx removed, showing 3 stigmatic lobes, style, and nectary . . . . Cross section through pistillate flower showing stigma, style and nectary tissue . . . . . . . . . . . Scanning electron photomicrograph of the pistillate flower nectary with stigma and style removed. 20x . . xi Page 11 11 ll 11 12 12 12 12 13 13 13 I3 Figure 13. 1A. 15. 16. I7. 18. I9. 20. Scanning electron photomicrograph of the pistillate flower nectary showing the stomate-Iike pores of the epidermis and where the style was attached to the bottom of the nectary cup. 100x . . . . . . . The stomate-like pores on the inner surface of the pistillate flower nectary as viewed through a scanning electron microscope . . . . . . . . . . . The outer surface of the cup-shaped pistillate flower nectary showing the absence of pores as viewed by a scanning electron microscope. 500x . . Outer upper edge of the cup-shaped pistillate flower nectary showing the absence of pores as viewed by the scanning electron microscope. 500x . Nectar removal in the field with Drummond microcaps The insertion of the microliter pipet between the stigmatic lobes to remove the nectar from the pistillate flwer O O O O O O O O O O O O O O O O The analysis of cucumber nectar with a Bausch and Lomb Abbe 3 L refractometer . . . . . . . . . . A honey bee removing the nectar of a cucumber flower xii Page 1A 1A 1A 1A 25 25 25 25 INTRODUCTION Agriculturally and ecologically, nectar secretion Is Important to man and other species of plants and animals. Many angiosperms pro- duce nectar to attract insect or other animal visitors to the flower. Through their visits the plant often benefits from the resulting pollination that may happen incidentally. Man relies on this flower- vIsltor relationship in the cross-pollinating of many agricultural crops. Honey bees alone account for about 80% of the pollination service to crops, USDA (1968), resulting In a yield of several billion dollars, McGregor (1973). Many of these crops would not be pollinated, If it were not for the nectar they produce. Honey is a second Important product of nectar secretion, since nectar Is the basic raw material of honey. The honey bee collects nectar from flower and converts it into honey through the evaporation of excess water along with the addition of enzymes which change the complex sugars present Into simple sugars. Some of the honey is used by the bee and the colony as a source of energy. Due to the honey bees natural hoarding Instinct, they may collect 100 times their own requirements, Faegri and Van Der Pijl (1966). The surplus honey In the United States in 1972 had a value of 65 million dollars, Money Market News, (1973). Economically though, the value of nectar secre- tion cannot be measured completely on the basis of commodity production In our nations agriculture. Many wild plants, shrubs, and trees through pollination associated with nectar secretion, furnish the animal kingdom with large sources of food In the form of fruits and seeds. Nectar also serves as a food for many animals other than honey bees. , Cook (1923) reported that nectar secretion studies date back to Ruellins (15A3). For many years nectar secretion was studied for academic reasons. Early researchers described nectaries and suggested that nectar was secreted to nourish the embryo, needed by the fruit buds, while others thought It was Injurous to them. Recent studies have been concerned with finding the optimum conditions for nectar secretion as well as understanding the actual secretion process. A knowledge of nectar secretion Is Important for many reasons. Beekeepers need this Information so they can locate apiarles close to areas which will provide a surplus of honey. In order to manage bee colonies for successful honey production, knowledge of the secretion cycles fOr the plants In the area Is needed. Such Information enables (the beekeeper to decide when he should install package bees, divide colonies, put on supers, remove honey, requeen and prepare colonies for winter. IOrchardists and growers who rent bees for pollination need to know what plants may attract bees away from the crops to be pollinated. Knowing why bees work one species of plant while disre- garding another, they should be able to more Intelligently locate bees for honey production and crop pollination. Spray poisoning may be redUced if the plants attractive to bees are known. Any Improvement in nectar production of a specific crop should Increase the attractiveness of the crop to bees and thus the effective- ness of pollination. Shuel and Pedersen (1953) and Shuel (19553) sug- gested two ways for increasing nectar production: (I) through breeding and selection of plants for high nectar production. Studies have shown wide hereditary differences in nectar yielding ability in bee- pollinated crops. (2) by cultural means, Including the provision of good conditions of soil drainage and the use of fertilizers favoring high nectar production. Plant breeders have been actively modifying crops for many purposes, generally associated with improved yield and quality, or adaptations to mechanized agriculture. Breeding crops which are more attractive to bees has enormous possibilities. For Instance, soybean industry leaders foresee great potential In developing hybrid soybeans with honey bees providing cross pollination of inbred lines. For effi- cient use of honey bees, nectar production would have to be built into new lines, Jaycox (1970). Bees visit flowers to gather nectar and pollen. Research sug- gests that attraction to a flower is visual, with aroma helping in specific identification. A reward of nectar or pollen is necessary for continuing visits to the plant. Other factors affecting bee visits appear to be chemical attractants in pollens, Hopkins, Jevans and Boch (l969), flower structure, nectar accessibility, quantity, sugar concen- tration, pH, flavor, and composition. ~ Some plant breeders have recently become more aware of the need to keep bee-pollinated crops attractive to bees. Problems have arisen In the production of hybrid onion seed, Bohart, Nye and Haw- thorne (1970) and Gary, Witherell and Marstow (I972). Nye, Waller and Waters (1971) found that Inbred lines vary In nectar attractive- ness to Insects. Plant breeders have expressed a need for more Information on attractiveness to bees and simplified ways of measuring it, so that significant factors of attractiveness may be readily monitored throughout breeding programs. Martin and McGregor (1973) suggested that apiculturists should be more intimately associated with breeding programs Involving bee-pollinated crops, to help maintain attractive- ness and usefulness to bees, and to elucidate ways in which pollina- tion affects breeding techniques and selection of genetic material. ~The production of pickling cucumbers in Michigan has recently undergone changes in cultural methods as well as breeding programs which have greatly increased the need for bees. The Industry has gone from multiple hand harvest to a single destructive harvest with mechan- Ical equipment. In order to have a single profitable harvest, plant populations have increased from less than 20,000 plants per acre to papulations up to and over 200,000 plants per acre. Secondly, the development of "gynoecious” lines of pickling cucumbers, Peterson (1960), made It possible to develop commercial hybrids which are pro- viding higher yields and more uniform growth. With the development of new gynoecious F hybrid cultivars,- 1 changes In the economics of production with new cultivation and harvest- Ing techniques, the need for this study evolved. Major objectives of the study were: I. To obtain a comprehensive picture of nectar secretion in cucumber flowers as Influenced by time of day, cultivar, age of flower or other factors. 2. To establish correlations between bee visits and nectar secretion. 3. To see if quantity and quality of nectar secretion Is being maintained in new cultivars. A. To progress toward a practical system of monitoring the attractiveness of new cultivars to bees during the course of a crop breeding program. CHAPTER I FLOWER AND NECTARY ANATOMY AS RELATED TO NECTAR SECRETION The Cucumber Nectary, Knuth (1908) described the nectaries of flowers In the order Cucurbitaceae, as naked fleshy cups formed by the fusion of the lower parts of the calyx and corolla. The nectaries consist of a layer of secretory tissue about 1 mm thick, and are provided with water- stomata. Members of the genera Cucumis, Cucurbita and Bryonia have flowers with concealed nectar. Staminate flower nectary.--The three-lobed button on the floor of the staminate flower is a rudimentary pistil (Figs. 1-3) and under favorable conditions, this glandular strudture may develop into a fertile pistil, making the flower bisexual. Therefore,.1t is called a pistillodium rather than a nectary, Heimlich (1927) and Chakravarty (1958); however, in line with popular usage, the term nectary ls used herein. Nemlrovich-Danchenko (l96A) referred to the nectary as a pro- tuberance with three or four sections (Figs. l-A). Four-lobed nectaries were also observed by Heimllch (1927). He found that the epidermal cells of the nectary were very small and smooth as compared with the epidermal cells lining the Inner wall of the perianth tube. Cook (1923) found that staminate flowers of pumpkin, Cucurbita pepo, had the calyx 6 and corolla united at the base, supporting a cup-shaped disk. The sides and base of this cup secreted and held the nectar. The glandular tissue was very deep, extending Into the interior for at least 1.5 mm. The epidermis was prominent, the cells being somewhat longer than in ordinary glandular tissue. The epidermal cells were somewhat broader than long, their outer walls curving only slightly, and were less granular than the underlying tissue. The epidermis was plentifully supplied with stomata which were only slightly sunken. Beneath the stomata were found the stomatal chambers and underthe epidermis were many layers of sub-epidermal cells. These cells were small, A-6 sided, and filled with granular protoplasm. Below the sub-epidermal cells were two regions of parenchymatous tissue, made up of cells larger than those of the sub-epidermis and several layers thick. Chakravarty (1958) referred to the pumpkin nectary as being trilobed. Bohn (1961) described the nectary of the staminate muskmelon flower as being saucer-shaped whereas Free (1970) called it a cup-like gland in the center of the receptacle. Pistillate flower nectary.--Free (1970) stated that a ring like nectary surrounded the base of the style in pistillate flowers of genus Cucurbita and in hermaphroditic flowers of Cucumis melo. Nemirovich- Danchenko (l96A) and Hayward (1938) described the nectary of cucumbers as having the form of a cup or ring surrounding the style In pistillate flowers (Figs. 8-12). Materials and Methods The structure of the nectaries was studied using a binocular and scanning electron microscope (SEM). To prepare for viewing with an SEM, cucumber flowers of different ages were picked from Michigan State University (MSU) field plots and transported to the laboratory In a wide mouth thermos bottle, Shuel (1968). Nectaries were dissected from the staminate and pistillate flowers and placed on two faced transparent tape which was attached to aluminum pedestals. They were surrounded by Walsco Television Tube Kote, placed within the chamber of a high vacuum evaporator, dried, and coated with gold palladium. After removal, the nectaries were placed In the specimen vacuum cham- ber of the SEM. Results and Discussion When flowers were picked on the day of anthesis, the nectaries contained a high amount of moisture which required a long period of evaporation. Excessive moisture did not pose a severe problem with nectaries of staminate flowers, but those of pistillate flowers formed a large bubble in the center of the cup, while In the evaporator. When gold palladium was added, the bubble burst and destroyed a large amount of tissue. To alleviate this problem, I successfully used day old pistillate flowers (Figs. 12 and 13). While attempting to focus the SEM on the surface of the four- lobed nectary from the staminate flower (Fig. A), many of the stomate- like pores of the epidermis began to close as the heat and beam of electrons were striking It (Figs. 5 and 6). This may Indicate that the stomate-like openings in the nectary surface can open and close as environmental conditions around the nectary surface change. In looking at various areas of the nectary of pistillate flowers, stomate-like pores were found only on the Inner surface of the cup and not on the outer edge or surface (Figs. 13-16). From an evolutionary standpoint, it would appear advantageous for the pistillate flower to concentrate Its nectar supply within the cup around the base of the style, with the stigma directly above it. Because of its loca- tion, the honey bees body must contact the stigmatic lobes in order to reach the nectar supply. The honey bee generally circles the nectary, inserting and retracting its proboscis several times, resulting in effl- cIent pollen distribution on the stigmatic lobes. Behrens (1879), cited by Cook (1923), divided nectar secretion into 5 classes based on the structure of different nectar secreting tissues. I believe the cucumber nectary would fit his fourth class; "secretion of nectar through the opening of stomata on the epidermal layer, which are sometimes sunken. Nectar passes from the stomatal chambers and then out through the stomata.” Fahn (1952) used a similar classification. Knuth (1908) described the nectaries of Cucurbitaceae as having water-stomata and Cook (1923) described the nectary of pump- kin as having slightly sunken stomates, with stomatal chambers below. Photomicrographs from the SEM show stomate-like pores in the epidermal layer (Fig. 6). The nectary surface is irregular and the area surround- ing the stomate appears to be slightly depressed. Comparison of SEM photomicrographs (Figs. 3-7 and 12-16) with photographs taken through a dissecting microscope (Figs. 1-2 and 8-11) 10 shows that the SEM Is superior for examining the nectary surface in fine detail. The SEM photomicrographs have magnifications ranging from 20-800 times actual size. No references were found on use of the scanning electron microscope for studying nectary structure. However, Schnepf (196A) and Findlay 8 Mercer (1971) used transmission electron microscopy along with histochemical tests to study the internal struc- ture and physiology of the nectary. The scanning electron microscope was a valuable aid In giving me a better understanding of the external surface of the nectaries. Proportion of Thregfiand Four- Lobed Nectaries Found in Staminate Flowers Cultivars having staminate flowers with a higher percentage of four-lobed nectaries (Fig. A) rather than the typical three-lobed (Fig. 3), tend to have larger nectaries. Several authors have shown a correlation between the volume of nectar and size of nectary. The phenomenon was found to be sufficiently prevalent to warrant further study. Materials and Methods During 1970 and 1971 the nectaries of staminate cucumber flow- ers were examined and the number of lobes recorded. Flowers of the cultivars SMR S8, 9805, Spartan Dawn, Spartan 27 and Piccadilly were grown at MSU research plots and the cultivar Pioneer (gynoecious Fl hybrid) with a 10% SMR 58 blend was taken from commercial fields in Eaton County. Fig. I. Nectary of the staminate flower as seen through a dissecting microscope. 2. View of the staminate flower nectary and stamens. 3. Nectary of the staminate flower as seen by a scanning electron microscope. 20x. A. Four-lobed nectary of the staminate flower as seen by a scanning electron microscope. 20x. Fig. 5. Scanning electron photomicrograph of the three-lobed nectary of the staminate flower showing the stomate-like pores of the epidermis. 80x. 6. Scanning electron photomicrograph of the three-lobed nectary of the staminate flower showing the stomate-like pores of the epidermis open. 800x. 7. Scanning electron photomicrograph of the four—lobed nectary of the staminate flower showing the closing of stomate-like pores of epidermis. 800x. 8. Cup-shaped nectary of the pistillate flower with stigma and style removed as seen through a dissecting microscope. Fig. 9. Cup-shaped nectary of the pistillate flower with droplets of nectar on the nectary tissue. 10. Pistillate flower with corolla and calyx removed, showing 3 stigmatic lobes, style, and nectary. 11. Cross section through pistillate flower showing stigma, style and nectary tissue. 12. Scanning electron photomicrograph of the pistillate flower nectary With stigma and style removed. 20x. I lllIll‘Hl-‘I' IHIIHHII I III,“ IH‘I‘ Illllallll [I‘ll III I l 10 Fig. 13. Scanning electron photomicrograph of the pistillate flower nectary showing the stomate-like pores of the epidermis and where the style was attached to the bottom of the nectary cup. 100x. 1A. The stomate-like pores on the inner surface of the pistillate flower nectary as viewed through a scanning electron microscope. 15. The outer surface of the cup-shaped pistillate flower nectary showing the absence of pores as viewed by a scanning electron microscope. 500x. 16 Outer surface of the cup-shaped pistillate flower nectary showing the absence of pores as viewed by the scanning electron microscope. 500x. 15 Results and Discussion Significant differences in the presence of three or four-lobed nectaries were found in different cultivars (Table 1). Three lobes were typical but of the cultivars tested, four-lobed nectaries were found to range from 0.7-12.32 of the total populations. The cultivars Pioneer and MSU 9805 contained the highest percentage of four-lobed nectaries. Oglgjn of the trait.--Baker (1972) suggested that the four- lobed nectary trait was inherited from the famale parent of the hybIrds. Therefore, the parents of the four gynoecious hybrids sampled (Table l) were tested to see if the source of this trait could be located. If found, then the plant breeder could possibly incorporate the four- lobed trait into new staminate lines. With the increased area of the nectary, nectar secretion might be improved and possibly the staminate flower would be more attractive to honey bees. Materials and Methods . To test the genetic origin of.the four-lobed trait, six parents that were:not.tested previously, SMR l8, MSU 183 G, 713-5, GY3, SMR 15 and Chipper, were planted during the summer of 1972. Thirty-seven days after planting, gibberellin (Pro-Gibb A7) at a rate of 50 ppm was sprayed on the predominately gynoecious lines to stimulate staminate flower production, Peterson and Anhder (1960). Each day the staminate flowers were picked from each of the parent stocks, and the number of three and four-lobed nectaries recorded. The gibberellin application 16 37 days after planting proved to be unsuccessful for staminate flower Induction, therefore,-the female parents MSU 183 G, 713-5 and GY3 were planted in a greenhouse on January 3 and February 9, 1973. Each planting consisted of ten plants per cultivar growing on cane poles. The first planting was treated with gibberellin at 22, 27 and 32 days after planting, and the second at 20, 25 and 30 days at a strength of 50 ppm. The staminate flowers thus produced were picked, examined, and the number of lobes recorded. Results and Discussion Pioneer In the original study had the highest occurrenceof 'four-lobed nectaries at 12.3% but its parents, GY3 and SMR 18, did not produce similar results. GY3 grown in the greenhouse did not produce any four-lobed nectaries and SMR 18 produced only 3.22 in the field (Table 1). Parents of MSU 9805, MSU 1836 and Chipper, also produced low numbers of four-lobed nectaries. In Chipper the four-lobed nectary occurred 0.AZ of the time and In MSU 1836 only 0.32. Of the male parents tested, SMR 15 was significantly higher than the rest, having the four-lobed nectary In 9.3% of the samples. In the greenhouse, 713-5 was the highest of the female lines with 3.7% occurrence. Both of these lines were parent stock for the hybrid Piccadilly. But In the original study, four-lobed nectaries only occurred 2.3% of the time In staminate flowers of Piccadilly. In the greenhouse only 713-5 and 1836 produced four-lobed nectaries in chemi- cally induced staminate flowers. The cultivar 713-5 produced 107 I7 staminate flowers over a twenty day period before a four-lobed nectary appeared. In the next 22 days the plants produced 28 of them with only lone day when none appeared. By that time, the chemical treatment was becoming ineffective, and the plants were reverting back to pistillate flower production. None of the 30 plants in the 2nd planting produced any four-lobed nectaries in 25 days of flowering. By that time, the effectiveness of the gibberellln had dissipated. Difference In field and greenhouse results may indicate that production of four-lobed nectaries is a response to certain environ- mental conditions, similar to parthenocarplc fruit production. Teidjens (1928) found that high light intensities reduced parthenocarplc develop- ment of cucumbers. A reduction in the amount of light resulted in a vegetative response which brought about parthenocarpy and ”easier fruit set,” implying that the percentage of flowers which deve10ped was higher. Connor (1969) found that the response was greatest In the fall and spring at MSU. Plants in the first planting which produced four-lobed nectaries were flowering during a time of reduced light in- tensity compared to those of the 2nd planting which did not produce any. Further research is needed to establish the factors which in- fluence the expression of this trait. The Nectary as Related to Floral Development The floral parts of the staminate flower appear in the follow- Ing sequence: calyx lobes, corolla lobes, stamen lobes and nectary lobes in Cucumis sativus and Cucumis melo, Judson (1929b, 1935). Il'l IIIIIIIIHI l8 m.o wmm 0mm— o.o mmm m >u m.~ mmm mum—m ._mco>o o.o om amm— o.o .N m >u o.o ~m~ mum—n N mc_ucm_m m.o mam umm_ o.o mmm m >o m.m no“ mum—n _ me_eee_e wNm_ omsoxcomLo a.o owe toee_;u m.m «a: m. mzm ~.m no: m. azm «um. xoOHm ucocmm II II m:o_uoocoe :.~ mun nu coucmam cmucmam mum—n m:o_uooc>m m.o mas c3mo coucmem teee_;u umm_ am: mso_uooe>m m.m mam momm .=.m.z II II m:o_o00coe o.~ :_m mm mzm w. «Zm m >o m:o_omoc>m m.~_ mom cooco_m m. azm m-m_~ mso_ueoc>m m.~ .mm >___emue_e 0—mz o_mEou oa>u comm coco—I: o~_m wuo_cm> mucocmm x . o_eEmm .mcm>_u_:o consaoso m:o_cm> mo mcozo_m oumc_Emgm c_ ucomoee mo_cmuuoc nono_IL30m cam mecca mo Logan: may mo c0m_tmeEoQ I ._ o_nmk l9 McLean (19A7) had the same results with Cucumis male, Helmlich (1927) reported a different sequence for cucumbers, namely; perianth tube, Istamens, nectary, calyx lobes and corolla lobes. He faund that the primordia of the nectary forms in the base of the cup. The usual three lobes of the nectary arise in a low spiral arrangement, the lobes a1- ternatlng with the stamens. Judson (I929b) found that Immediately after the primordia of the stamens appear, three small lobes may be recognized eqhidistant from one another, near the bottom of the receptacle, below and within the stamen lobes. These lobes grow toward each other and form a small three-lobed nectary. Kirkwood (1905) reported that pistillate flowers of various Cucurbitaceae have the floral parts develop in the following sequence: calyx lobes, corolla lobes, staminodium or stamen lobes and pistil lobes. Judson (1929A, 19A9) while working with the pistillate flowers ' of Cucumis sativus and Cucumislmglg_reported similar findings. Judson found that the nectary tissue of cucumber is differentiated from the receptacle after the carpel lobes have extended upward into the perianth tube. Between the base of the perianth tube and the style, a group of cells become meristematic and a continuous ring of nectary tissue 15 formed surrounding the style. The nectary tissue is composed of cells with large nuclei and coarsely granular cyt0plasm. The Vascular Tissue of the Nectary The concentration at which nectar leaves the nectary cells ap- pears to depend on the anatomy of the vascular system supplying the nectar and on the sugar concentration in the phloem and/or xylem of 20 the nectary vascular supply, Frey-Wyssling and Agthe (1950), Agthe (1951), Zimmermann (I953), Shuel (I956), Huber (1956) and Frey-Wyssling and Hausemann (1960). Esau (1953), Agthe (1951), Frey-Wyssling and Agthe (1950) and Zimmermann (1953) found that highly concentrated nectar, essentially originates from phloem tissue whereas plants that produce high volumes of dilute nectar have only a few sieve tubes to transport sugars to the nectary, and abundant xylem. The qUantity of nectar secreted Is a function of the carbohy- drate supply to the nectary Agthe (1951), Wykes (1952c), Shuel (1955b, 1956) and Waddle (1970). Wykes (l952c), Shuel (1955b), and Czarnowski (1952) demonstrated that curtailing carbohydrate synthesis and trans- port to the flower by defoliation and phloem ringing, reduced nectar production in various species of plants. Miribel (1815) as cited by Cook (1923) found that the cells of nectary tissue are traversed by vascular ramifications. Caspary (I8A8) cited by Fahn (1952) found that nectar originated in nectary cells and not from vascular bundle secretions. Cook (1923) observed vascular bundles in all glands that he studied. They were found in close prox- imity to each other running either parallel or at right angles to the nectary tissue. Sometimes they extended into the nectary tissue. Beutler (1953) stated that vascular bundles ramify throughout the surrounding areas, but seldom penetrate the nectary. Even after the vascular tissue has supplied the nectary with carbohydrates and water, it appears that ultimately nectar secretion depends on the metabolic activity of the nectary itself, Agthe (I951), Frey-Wyssling, Zimmermann and Maurizio (195A), Ziegler (1955). and Shuel (1967). 21 McLean (19A7) while studying the staminate flowers of Cucumis 5512 found that the pedicel contained 10 main vascular bundles. Chakravarty (1958) while working with staminate flowers of Cucumis Ln_e_l_g and Cucumis sativus also found that the pedicel had 10 bundles arranged In a single ring. After further branching, the bundles fuse at the receptacle forming an Irregular broad ring. The outer part of this ring supplies the sepals and petals. The glandular nectary re- ceives a number of weaker and shorter bundles from the Innermost part of the vascular cylinder. In all species of CucurbitaCeae that he examined, the traces of vascular bundles for the nectary came from the inner side of the stele (vascular tissue forming a cylinder running through the stem) and ran through the inner surface of the receptacle. Traces for the nectary are far more numerous but they are smaller and weaker than those supplying the petals, sepals and stamens. These traces are arranged In a circle In the outer wall of the nectary, or sometimes scattered within where they often coalesce. Heimlich (1927) found that the vascular bundles in the pedicel of the staminate cucumber flowers vary In number. They may form a continuous or nearly continuous ring in the lower portion of the recep- tacle. Slightly above this, the vascular tissue appears as a general plate or low dome-shaped expanse. Some of the branches from this plate enter the nectary. Each group supplies one of the lobes of the nectary. Within the fleshy portion, there is considerable branching and anastomosis of the vascular bundles. Judson (I929a) found that the pistillate cucumber flower had ten main bundles at the upper extremity of the pedicel. At the narrow 22 neck of the flower the five bundles of the outer cycle (the main sepal bundles) fork, and five branches, extend inward and upward to the nectary tissue where they branch and anastomose freely. The nectary tissue is Well supplied with branched vascular bundles. Cook (1923) found that the two regions of parenchymous tissue In the pumpkin nectary contained extremely thick vascular bundles that ran in every direction. The vasCular bundles ended in the nectary tissue and were very abundant. Chakravarty (1958) found that the pump- kin pedicel had 12 vascular bundles arranged In two rings. The bundles fused In the receptacle. From this fusion, many weak and short traces pasSed to the nectary. The Procedure Used to Remove Nectar from Staminate 92d Pistillate Cucumber Flowers The cucumber plants used for nectar secretion studies were grown at the Collins Road plots, Michigan State University, East Lans- Ing, Michigan. Nectar removal from the cucumber flowers proved to be easily done since the flowers are large and the nectary accessible. Nectar was removed with Drummond microcaps, lO microliter size (Fig. 17). To improve the action, the microcaps were attached to plastic tubing for mouth suction in addition to the capillary effect. The reverse action was used to empty the tubes. The tubes were inserted into the nectaries between the stigmatic lobes of the pistillate flowers and between the anthers of the staminate flowers (Fig. 18). Two to three insertions were needed to remove the nectar from the flowers. 23 The pipets were Al mm long and held 10 microliters. By measur- Ing the amount of nectar within the tube to the nearest mm and figuring proportionately, the volume of nectar was determined. Next, the nectar samples were placed on the prism of a Bausch and Lomb Abbe 3L refrac- tometer to determine the refractive index and total solids present (sugars) (Fig. 19). Volumes of less than O.A9 microliters generally did not make a large enough droplet on the prism, so refractometer readings could not be taken. Corrections for temperature were made for each sample with tables found in the Association of Official Agri- cultural Chemist Handbook (1950). The total weight of sugars present which takes into account both volume of nectar and sugar concentration, was figured by multi- plying the volume in microliters x the specific gravity of the percent sugar present x the sugar concentration. Tables for determining the specific gravity of a sugar solution are also found in the handbook (pages 711-12). 'To prevent bees from removing the nectar, plants were enclosed in nylon screened cages or the flowers were bagged one day prior to anthesis in 2.5 Inch square organdy bags. For most samples, flowers were picked and nectar removed shortly I afterwards in the fieldhouse adjoining the plots. For studies that re- quired the flowers to remain on the plants, microcaps were taken into the field in one section of a plastic petri dish, being kept separate by an Index card partition (Fig. 17). After removal, the samples were taken into the fieldhouse for refractometer readings. 2A Nectar removal from flowers other than cucumbers may present some problems especially for compound flowers from the families Com- positae and Leguminosae. Methods other than microliter pipets may have to be employed. Possibilities would include centrifuging, Swanson and Shuel (1950), absorption of nectar on weighed filter paper strips, Kenoyer (1917), and the leaching out of nectar by soaking flowers in water, Livtzeva (195A). Comparison and discussion of the various methods was done by Skirde (1960, 1961), Yakovleva (1966) and Beutler (1953). In order to monitor the attractiveness of new cultivars to bees during the course of a crop breeding program, some refractometer read- ings may be required. Small, less dependable, hand refractometers are available that can be taken directly into the field. Nectary Size and Nectar Secretion Free (1970) stated that the size of the nectary may influence the amount of nectar secreted. Fahn (19A9a, 19A9b) in sampling nectar from 66 different species of plants found a definite relationship be- tween the quantity of nectar secreted and the size of the nectary but no correlation was found between the concentration of nectar and nectary size. In Cucurbitaceae, the volume of nectary tissue is larger in the pistillate flower than in the staminate flower. Timenskii (1968) found a positive relationship between the size of the flower and nectar yield. Beutler (1953) reported that the quantity of nectar secreted and its sugar content are related to the size of the flower, which partially determines the size of the nectary. Waddle (1970) found that the rate of nectar flow, in general, was a function of the nectary area in cotton. 25 ecu mcm>oeot won >oco: < .ON Sc...I\—u IIJI..I..I I “I II . .LouoEOuumLmoL 4 m onn< £504 ocm somsmm m £u_3 Lmuooc Loganoau mo m_m>_mcm use .m_ .Lozopm oum___um_a any EOE» Leuoo: ecu o>0EoL cu mono_ o_umEm_um osu coozuon uoe_a Lmu__oLo_E on“ $0 co_ucomc_ och ON .w. .mamooLo_E ocOEE3Lo cu_3 v_o_m exp c_ _m>oeoc cmuooz .m_ .m_u 26 Materials and Methods During the course of this research, 1968-1973, five studies Involved the measurement of nectaries from staminate and pistillate flowers. Correlated nectar studies were carried out, using the same flowers. 12§§A,--Measurement of the nectaries from staminate and pis- tillate flowers were made to the nearest mm. Eight seed lots of 10 plants each were used. Each morning, all flowers on the 80 plants were picked, counted, petals and nectaries measured. The eight seed lots used were: a. Spartan 27 b. Spartan Dawn - no pollinator c.- Piccadilly - Med. 1, no pollinator d. Piccadilly - Med. 11, no pollinator e. Spartan Progress (MSU 35 C x 381) f. MSU 35.6 (Gynoecious)t g. Piccadilly - Med. 11, no pollinator h. SMR 58. 12§§§3--A second replication of the previous planting was made later In the summer. Five plants from each of the cultivars f, g, and h were covered by a 6 ft2 nylon screened cage. The plants grew upward on cane pole stakes, and the flowers were harvested at 9:30 a.m. The flower node was recorded, petals and nectaries measured before nectar removal. 27 1969.--Nylon screen cages 6 x 12 ft2 were placed over plants of the cultivars SMR 58 and Spartan Progress. Pistillate flowers were picked at 11 a.m. and A p.m. The petal width, nectary width and ovary length were recorded prior to nectar removal. 1970.--The nectary width of staminate and pistillate flowers from the cultivar Piccadilly Med 1 were measured to the nearest mm. 197l.--To get a more accurate determination of the size dif- ferences between the nectaries of the staminate and pistillate flowers, they were measured under a dissecting microscope with an ocular micro- meter. The width and depth of staminate flower nectaries were measured using 15x oculars and 0.7x objective lenses. Cultivars Spartan 27 and SMR 58 supplied the staminate flowers. The width, depth and thickness of the sides of the nectary cup of pistillate flowers of MSU 9805, MSU 356 and a parthenocarpic cultivar (MSU 6902 6) were measured. Results 1§§§5,--Ih the cultivars that produced both staminate and pistillate flowers, the average width of the nectaries of pistillate flowers was over one and a half times that of staminate flowers (Table 2). Means of staminate flower nectaries ranged from 2.6-2.9 mm (overall mean, 2.8 mm) In diameter, whereas pistillate flower nectar- ies ranged from A.2-A.6 mm (overall mean, A.A mm). Thus, pistillate flower nectaries were approximately 1.6 times as wide as staminate flower nectaries. The smallest pistillate flower nectary measured was 2 mm and the largest 8 mm whereas the smallest staminate flower nectary 28 was 1 mm and the largest, 6 mm. 0f the 795 staminate flower nectaries measured,.88% were 2 to 3 mm wide and of the 1079 pistillate flower nectaries, 92% were A to 5 mm wide (Table 3). The average size of petals of pistillate flowers was larger than that of staminate flowers In all cultivars but the differences were not nearly as great as was shown by the nectaries. Means of staminate petals averaged from A2.5-A6.0 mm in width and pistillate ranged from AA.5-A9.l mm (Table 2). The overall means, considering all varieties, was AA.A mm for staminate flowers and A7.2 mm for pistillate flowers. The average pistillate flower petal was approximately 1.06 times as large as that of the staminate flower. To more fully assess relationships between nectar secretion and size of nectary, the data was sorted by nectary sizes and sex, then analyzed. A positive correlation was found between: (1) nectary size and petal diameter (Table A), (2) nectary size and volume of nectar produced (Table 5), which is in agreement with Beutler, Fahn, and Timenskii. Overall there was a positive correlation between nectary size and total weight of sugar in the nectar, even though it was not significant In pistillate flowers (Table 7). No significant correla- tion was found between nectary size and sugar concentration (Table 6). When correlation coefficients were squared, there was an 18.2% associa- tion between petal size and nectary width, 11.8% between volume of nectar and the nectary size, 0.28% for sugar concentration and nectary width, and 5.1% for total weight of sugar and width of nectary. l9688.--ln this planting the staminate flower nectaries aver- aged 2.3 mm whereas the pistillate flower nectaries ranged from 29 um pcmo_m_cm_m >_;m_n on on Eosu 0::Om .Aumou u ucoozumv _o>o_ >u___nmnoca .0.0 050 couoEm_v Logo—w 0cm Luo_3 >cMuuoc com memos ._mco>o mo :Om_cmeEOo mm.o H «.ma 0m.o H m.#: mo.o H.:.J mo.o H w.~ mcmoE __mco>0 mno_ mmm m_m00h mn.o H m.:: 0:.0 H N.¢: no.0 H m.: mm m0.0 H m.~ 0_~ mm «2m 3.0 a .0: $6 a ma: moé e mi Q: woe a m.~ R ._Sefzo.<>:_eeBE 3.0 a 7m: 1 3.0 e. NJ on I N 0mm 3: 8.0 H nos 1 moé a mi 2. 1 _ $88.... anthem mm.o H o.n: Nm.o H m.:: no.0 H.:.: mo_ 00.0 H N.N o~_ __ voz >___omuo_m _m.o H w.m: on.o H o.m# 00.0 H m.# N__ no.0 H w.~ mm _ to: >___tmuo_m $6 a mo: mmé H a.me mod H 0.: a2 8.0 « fim mm :38 Steam mn.0 H m.m: _:.o H m.m: mo.o H m.: m: $0.0 H o.N mm_ RN coucmaw Aeav Logo—m AEEv c03o_m AEEV zcmuooc ouwm AEEV Ncmuooc oN_m no. ovum mum—._om_m oumc_Empm L030.» mum—._um_m o_oemm cozo_w ouoc_Emum o_aEmm .mem>_u_:o consoooo _mco>om to» mcozo_m oumc_Em~m ocm mum—._um_o mo coop: >couuoc 0cm Louoem_o Logo—m ommco>m one I .N o_nmh 30 A.O-A.5 mm (Table 9). The average width of the pistillate flower was 1.7 to 1.9 times wider than that of the staminate flower. The pistillate flower nectaries ranged from 3 mm to 5 mm whereas the staminate flower nectaries ranged from 1 mm to 5 mm. Of the 366 staminate flower nectar- Ies measured, 97% were In the 2 to 3 mm range and of the 61 pistillate flower nectaries, 95.1% were in the A to 5 mm range (Table 3). The average petal size of pistillate flowers was larger than that of stam- Inate flowers In the two cultivars that produced both, but the differ- ences were not as large as those of the nectaries (Table 9). Correlation coefficients were established in which nectary size was compared with petal size, volume of nectar, sugar concentration and total weight of sugar in the nectar for the pistillate flowers of MSU 356 as well as staminate flowers of Piccadilly and SMR 58 (Table 9). Positive correlations were established between nectary and petal size as well as between nectary size and total weight of sugar for 2 of the 3 comparisons which is In agreement with 1968A. The 1968A study also~ showed a positive correlation between nectary size and volume of nectar in staminate and pistillate flowers, but in this study only pistillate flowers showed such a relationship. Also the staminate flowers of SMR 58 showed a positive correlation between nectary size and sugar concentration which was not found In the previous study. Squaring of the correlation coefficients showed ranges of 8.1 - 21.9% association between nectary width and petal size, 1.8 - 17.6% between nectary width and volume of nectar, 0.5 - 8.1% between nectary width and sugar con- centration, and 5.6 - 2A.O% between nectary width and total sugar present. 31 The values for cultivars producing staminate flowers were similar, but values for pistillate flowers were quite different (Table 9). This could be because small sample sizes of pistillate flowers were used. 12623--In the 1968A study, the average pistillate flower nectary width was A.5 mm for SMR 58 and A.3 mm for Spartan Progress. In this study the values for these two cultivars were reversed and petal sizes were slightly less than before. The smallest pistillate flower nectary was 2 mm in width and the largest 6 mm. Nectary diameters of 93.6% of Spartan Progress flowers, measured in the A to 5 mm range while SMR 58 had 89.3% in this range (Table 8). Since a positive correlation was found between nectary size and petal size (Tables A and 5), and Connor (1969) found a positive corre- lation between ovary length and number of ovules, the ovules of the flowers were measured to see if there was a correlation between the nectary width and ovary length. The ovary length of SMR 58 averaged 20.A mm and Spartan Progress 18.7 mm (Table 11). Correlation coefficients were computed comparing nectary size with petal width and ovary length. Positive correlations were found between: (1) nectary size and petal size and (2) nectary size and ovary length. The correlation coefficients showed an 11.6% - 11.8% association between nectary size and petal size and a 17.8% - 32.8% association between nectary size and ovary length (Table 11). Analysis of the nectar secretion data showed correlations similar to the previous studies. Positive correlations were again 32 found between: (1) nectary size and volume of nectar and (2) nectary size and actual weight of sugar In the nectar for both morning and after- noon sampling times. A positive correlation between nectary size and sugar concentration was found only for the morning sampling period. The afternoon correlation coefficient was negative but the Student's t test showed It was not significant (Table 10). 1970.--The nectaries of pistillate flowers from the cultivar Piccadilly were 1.6 times larger than the staminate flower nectaries. Nectaries of pistillate flowers averaged A.2 mm and those of staminate flowers 2.6 mm. The smallest pistillate flower nectary measured 2 mm ' and the largest 6 mm whereas the smallest staminate flower nectary was 1 mm and the largest 5 mm. Of A53 staminate flower nectaries measured 89.2% were in the 2 to 3 mm range and of 935 pistillate flower nectaries, 82.0% were In the A to 5 mm range (Table 3). Again the Student's t test, showed a positive correlation between nectary size and petal width for both staminate and pistillate flowers. There was a 3A.9% association between nectary and petal size for stam- V lnate flowers and A9.2% for pistillate flowers (Table A). Significant correlations were found between mean petal size and nectary size with two exceptions (Table A). 1971.--Again pistillate flower nectaries were wider than those of staminate flowers (Table 13). The overall average diameter of the pistillate flower nectary was 3.6A mm whereas the staminate flower nectary was 1.98 mm; therefore, the pistillate flower nectaries aver- aged 1.8 times as wide as those of staminate flowers. 33 mo_tmuooc Lozo_m mum—._um_m u m mo_LMuooc ooze—m oumc_Emuw u < oN_m o_aEmm u 2 mg mm: 3 00m m3. as .32 I- I- I I- I- I- I- I- x. .o _ I- a gem 1.. -1 I... I- 1.. I- I- 1. $5 N i- o a: .2 .N om I- o I- i- I- 1.. §.~ 3 .E .o _ see xmém .Nm fie _ $3. 2 fie _ a.m.: me: a: m .5 xx.uq 0:: Nu.n mm $5.0m w: xm.0 N $0._m 0mm $_.m N“ as: .25 :: fem RN a.m.: m gain mm. a.m.: mm $3 03 :5 $50 A x. .mM K. I- o Noam mNN § .o _ .2 .3 m2 :5 I- o a.m.u m. I- o x~.~ m I- o .e: : as. m z < z m z < z m z < z 3; H o n mama. _ _ 4 $9 0 .eaoLm o~_m :umo c_;u~3 0:30» mcozo_m mum—._um_a 0cm oumc_Emum eocm momcmuooc mgu mo acoume I .M m_QMH 3A .A umou cOmmLooEoo o_omu_:e _:ox I cmEZoz I ucoosum v _o>o_ >u__mnonoLo gm 050 um ucoLomm_v >_ucmuwm_cm_m Ho: oLm Louuo_ __mEm 05mm osu >0 oozo__om can—on some 0. meme: ._e>o_ >a___eeeoLa _oo. may be aeee_c_ee_m «he muco_o_mmoou co_ue_oLLoo u L as: .. .9 astmm~:.o u L Aawem_o ._eteso Ammm u :0 Amm: u :0 Aumo_ n :0 Aemn n =0 HHH0_0N.0 u L «Hemomm.0 n L Heawm:m.o n L Hee0omm.o u L III III III III III _ . III 0 saw ..I -I- II- II- aeuo.0 H o.mm N -I- o ESL 0._ H 0.:m 0N III 0 o... H w.mm mu III _ EE0 m.0 H 0.0m .Nm III _ 0N.o H m.m: ::: am:.~ H 0.0: m 55m «.0 H ~.:: 0:: 0.0 H m.om mm um.o H.:.0: cam em.o H m.w: «L as: m:.0 H 0.0: mum um.o H 0.0: NNN _._ H m.~: _m m~.0 H m.m: 5:: 55m m~.N H m.:m m :.0 H N._: mn_ III _ m.0 H 0._: :mm EEN --- o o.~ H o.:m m. -I- o :._ H _.om _. as. AEEV oN_m AEEV wN_m AEEV oN_m AEEV oN_m .ouoa .0>m .muoo .m>m .ouoa .0>m .muoo .0>m mLozo_m o~_m mLozo_m o~_m mLozo_m o~_m mLozo_w o~_m suo_3 mum—._Hm_m o_eEmm oumc_Emum o_eEmm oum___um_m o_oEmm oumc_Emum o_osom >Lmuuoz _ one. o H < mom. _ .oN_m .muoa no.3 oN_m >Lmuuoc mo co_um_oLLoo I .: o_pmh 35 Table 5. - Correlation of nectary size with volume of nectar produced. Nectary Sample Staminate flowers Sample Pistillate flowers width size vol. of nectar size vol. of nectar (microliters) (microliters) 1mm 2 0.86 t 0.39abcd 0 --- 2mm A6 1.22 t 0.12 def l --- 3mm 55 1.A1 t 0.16 c fg 10 2.32 t 0.50 ij Amm 10 2.56 t 0.63a h 163 2.01 t 0.16 1 5mm 2 2.06 t 1.12 b e gh 1A5 2.9A t 0.20 j 6m 0 "'-"' A 7067 t 0096 I' = 0.268890% 1‘ '-"- 0.178759“? (0 = 115) (n-= 323) Overall r = O.3AAO*** (n = A38) ** Significant at the .01 probability level. *** Significant at the .001 probability level. Means in each column followed by the same small letter are not significantly different at the 5% probability level. _parison test) (Student-Newman-Keul multiple com- Table 6. - Correlation of nectary size with sugar concentration of nectar. Nectary Sample Staminate flowers Sample Pistillate flowers width size % sugar size %.sugar 1mm 2 39.0 ._L 6.95;. o --- 2mm A2 Al.8 t 0.82a O --- 3mm 51 A2.6 t 1.16a 9 A1.6 t 2.01 bcd Amm 10 Al.3 t 1.Ala 159 A2.9 t 0.39 c e 5mm 2 3A.l t 7.553 1A1 A3.5 t O.A3 'de 6mm 0 --- A ' 36.2 t 2.1A b r = 0.0213 n.s. (n = 107) Overall r = 0.0536 n.s. (n = 320) n.s. = Not significant r = 0.0295 n.s. (n = 213) Means In each column followed by the same small letter are not significantly different at the 5% probability level. comparison test ). ( Student - Newman - Keul multiple 36 Table 7. - Correlation of nectary size with total weight of sugar in the nectar. Nectary Sample Staminate flowers Sample Pistillate flowers width size wt. of sugar (mg) size wt. of sugar (mg) 1mm 2 0.32 t 0.11a . O --- 2mm A2 0.59 t 0.06a O --- 3mm 50 0.72 t 0.08a 9 1.17 t 0.17 bc Amm 10 0.97 t 0.1Aa 159 1.3A t 0.07 cd 5mm 2 0.68 i 0.2Aa 1A1 I.A6 t 0.09 b d 6mm 0 --- A 3.16 t 0.31 r = 0.2101* r = 0.1096 n.s. (n = 106) (n = 313) Overall r = 0.2258*** (n = A19) n.s. = Not significant. * = Significant at the .05 probability level. *** = Significant at the .001 probability level. Means In each column followed by the same small letter are not significantly different at the 5% probability level. (Student - Newman - Keul multiple comparison test). Table 8. - Percent of the pistillate flower nectaries found within each size group. (1969) SMR 58 Spartan Progress Size Sample size % of group Sample size % of group 1mm 0 0.0 O 0.0 2mm 1 1.0 0 ’ 0.0 3mm 7 6.8 I 3.2 Amm A5 A3.7 1A 45.2 5mm A7 A5.6 15 A8.A Totals 103 31 37 ReHmeu e m7_H@3 e efioHEJ ee~0L~.o u L «em:m~.o . L e~m_.o h L mo.o H mm._ _N_ L~.o H__.m: _~_ o_.o H mo.~ o~.o H 0L._ 0 ~m.. H _.m: o m~.o H m~.m _om~.o u L Lo__.o u L mm:_.o u L no.0 H o:._ 00 0m.0 H «.m: 00 m_.o H m0.~ «mm0:.0 u L mm00.o u L Hmm_:.o u L n_.o H n:._ mm o:._ H o._: mm 0:.0 H 0m.~ ._o>e_ >HL__aeeoLe _eo. has be beeULLLemLm u ass ._e>e_ >a___eheoLe _o. one uh seeeLLLeeLm n es ._e>e_ >a___aeeoLe me. sea as beeuLLLeeLm n s n :m._ H :.N: __ :_.0 H m.: HHH:00~.0 u L ma. ~:.o H m.o: mm. :o.o H m.~ e m~.~ H _._: m_ mo.o H _.: HHNmmN.o n L 00 :m.0 H ~.mm 0__ 00.0 + m.~ Hsmwo:.o n L mN no.0 H 0.m: mm 00.0 H 0.: m_ mLozo_m cum—._um_m mLozo_m emu «beeLEeum mw.mmm. m— mLOZO—u— oue___emLe mLozo_m 0.. oumc_Emum >___eeuu_e mLozo_m mm mum—._um_m mLozo_m II oumc_emum 0m 0m: x AmLou~_oLumEV AEEV AEEM A060 .0000 oE:_o> oN_m cuo_3 meam mo o~_m meam oN_m Lmuooc oN_m _muoa oN_m >Louooc o~_m Lm>_u_:o .uz ommLo>< o_eewm ommLo>< o_oemm ommLo>< o_aEmm ommLo>< «_oemm ommLo>< o_eEmm Am 00m_v .Lmuuoc ecu c_ meam mo u;m_oz _muoH vcm co_umLucoucoo mesm .Lmuooc mo oE:_o> .o~_m _Muoo ;u_3 oN_m >Lmuooc mo cohum_0LLou can I .m o_amn 38 ._o>o_ >u___nmnoLa _00. 0:“ Ho ucmo_m_cm_m n HHH ._o>o_ >u___nmnoLe _0.o;u um acmo_m_cm_m n «H ._o>o_ >u___nmnoLa mo. ago um ucmu_w_co_m n H .ucmo_w_cm_m uoz n .m.: memm:.0 n L .m.c :~m_.onu L HHN00:.0 u L 0m 20 00“: HHHom_m.o u L sm:m~.o u L «Hmmum.o u L Hm z< oou__ muco_o_mmooo co_uw_oLLoo 0:.0 H mm.m on._ H m.~: m_._ H :~.L 0_ ze co”: _m.o H LN.N mm._ H _.Nm 00.0 H _:.m m_ z< oo __ mmoLmoLe cmumem mm.o H mm.: 0_.~ H _.:: m_._ H :m.m 0m 20 00“: m_.o H :m.~ ~:._ H o._: m:.o H -.m aw z< con—— flaw. Amev meam 00 A$V .ucoo A_:v ._o> oN_m u;0_oz .o>< mezm .0>< Louooc .0>< o_esmm Lm>_u_:o .Am0m_o Lease: sea eL Lease mo u:m_03 .0000 0:0 co_umLucmucou meom .Lmouoc mo oE:_o> cu_3 0N_m anuuo: mo co_um_oLLou I .0. o_nmn 39 Since scanning electron micrographs showed that the stomate- like pores through which nectar was secreted were found only on the Inner surface of the cup In the pistillate flower nectary, the secret- .lng area can be calculated. Figs. 8 and 11 show that the style takes up 2A.A% of the total area of the nectary in the bottom of the cup. Therefore, a hypothetical model for figuring the secreting surface area of the pistillate flower nectary, would be a cup-shaped structure with an inner width of 2.30 mm at the top and .89 mm at the bottom with a depth of 1.0A mm (Table 13). Two different geometric models were used for figuring the surface area. The inner surface of the cup was considered as a hemis- phere. By using the depth from a central point as the radius of that sphere and subtracting the area taken up by the base of the style, an area of 6.17 mm2 was calculated. The radius at the top of the cup was found to be 1.15 mm which was greater than the depth; therefore, a radius of 1.095 was considered a reasonable estimate and gave an area of 6.91 mmz. Another way to calculate the area Is to consider the curved ‘ surface as a frustrum of a right cone with a base radius of 1.15 mm aruj the lower radius equal to .AA5 mm which would represent the base <3f the style. The frustrum would have an altitude equal to the depth. 11115 gives an area of 6.30 mm2 which probably is the best estimate. The upper surface of the staminate flower nectary constitutes a (:ircle with a diameter of 1.975 mm, if there were complete fusion of the 3 lobes that make up the nectary. Figs. 1 and 3 show that this Is A0 not quite the case. Graphically, the nectary in Fig. 1 contains ap- proximately 85.7% of the total area of the circle with a diameter equal to the width of the nectary. This hypothetical surface has an area of 3.06 mmz. Subtracting 1A.3% of the area, which was not part of the actual nectary, yields an area of 2.62 mmz. From Fig. 3 It appears that stomate-like pores occur on the overlapping edge of the staminate flower nectary, along with an observed unevenness of the nectary surface; both of these factors would increase the nectary area; therefore, the value of 3.06 mm2 would provide a reasonable estimate of secreting area. From these values It would appear that the pistillate flower nectary has approximately twice as much secreting surface as the staminate flower nectary. Overall the staminate flower nectary measured 1.98 mm wide and .98 mm thick whereas the pistillate flower nectary measured 3.6A mm wide, with the edges .67 mm thick and a depth of 1.0A mm (Table 13). Discussion The following points summarize the results of the 5 studies dealing with nectary size. 1. In all cases the nectaries of pistillate flowers ranged I..6-1.9 times as wide as the nectaries of staminate flowers. 2. The average width of the staminate flower nectaries was _‘frcun 2.0-2.9 mm whereas the pistillate flower nectaries averaged from 3.6-A.6 mm. 3. The smallest pistillate flower nectary measured 2 mm and the largest 8 mm. A1 Table 11. - Correlation of nectary size with flower size and ovary length (1969). Cultivar Sample Avg. nectary Avg. petal Avg. ovary size width width length SMR 58 103 A.3 t 0.07 mm A6.7 t 0.57 mm 20.A t 0.30 mm r = 0.3AOA*** r = 0.5729*** Spartan 31 A.5 t 0.11 mm A7.5 t 0.69 mm 18.7 t 0.39 mm Progress r = 0.3A35 n.s. r = O.A225* Overall r = 0.3AI6*** r = 0.5159*** n s = Not significant. * = S'gnificant at the .05 probability level. *** = Significant at the .001 probability level. Table 12. - Average petal size and ovary length of SMR 58 and Spartan Progress (1969). [ SMR 58 ] [ Spartan Progress ] Size N Avg. petal Avg. ovary N livg. petal Avg. ovary size length size length 2mm 1 --- --- --- --- 3mm 7 A3.9 f 2.A2 18.1 t 1.01 l --- --- Amm A5 A5.3 t 0.9A 19.1 t 0.36 1A A7.0 t 1.13 18.0 t O.AA 5mm A7 A8.3 t 0.66 22.0 t 0.37 15 A8.3 t 0.80 19.1 t 0.56 6mm 3 52.7 e 2.60 2A.7 t 1.33 1 --- --- -Table 13. - The average dimensions of the pistillate and staminate flower nectaries of several cucumber cultivars as measured by an optical micrometer. Sex N Diameter Thickness Depth Cultivar (mm) (mm) (mm) SMR 58 M 101 1.95 "I: 0.02 I.08 I: 0.02 --- Spartan 27 M 101 2.00 t 0.03 0.88 :1: 0.02 --- MSU 350 F 109 3.33 t 0.05 0.57 t 0.01 0.97 t 0.02 9805 F 115 3.80 t 0.03 0.65 a; 0.01 I.05 t 0.02 MSU 6902 G F 28 3.78 t 0.08 0.78 t 0.03 1.10 t 0.0A A2 A. The smallest staminate flower nectary measured 1 mm and the largest 6 mm. 5. The diameters of the staminate and pistillate flower nectaries tend to fall within 2 class sizes. From 88% - 97% of the staminate flower nectaries were from 2 to 3 mm and 82% - 95% of those from pistillate flowers were A to 5 mm wide. 6. Consistently, I found positive correlations betWeen: (a) nectary size and petal diameter, (b) nectary size and volume of nectar, (c) nectary size and actual weight of sugar In the nectar, (d) nectary size and ovary length but not for nectary size and sugar concentration. 7. The secreting surface area of the pistillate flower nectary measured approximately twice that of the staminate flower. 8. The squaring of correlation coefficients showed an 8% - A9% association between nectary size and petal diameter, 1% - 18% association between nectary size and volume of nectar, .3% - 8% associa- tion between nectary size and sugar concentration, 5% - 2A% associa- tion between nectary size and total weight of sugar and 18% - 33% association between nectary size and ovary length. Other research workers have shown positive correlations between: (a) nectary size and petal size and (b) nectary size and volume of nectar in several other plants. Since consistent positive correlations were found between actual weight of sugar and volume of nectar to nectary size, these characteristics should be usable In a breeding pro- lgram. Nectar volume and sugar concentration present in flowers largely determine attractiveness of a plant to bees. These studies indicate A3 that attractiveness of a crop to bees could be readily monitored dur- Ing a plant breeding program In that they have demonstrated a corre- lation between nectary size and nectar production which might pro- vide the breeder with an additional indicator of attractiveness to bees. In a cultivar known to secrete nectar, selection for larger nectaries could further increase attractiveness. Plant breeders and growers have encountered major problems in production of adequate seed yields in hybrid onion and carrot. Adequate pollination appears to be an important part of the problem. In general, in past breeding of bee-pollinated .crops, no adequate tools for measuring potential attractiveness to bees have been available, so this aspect of a breeding program has been largely overlooked. I feel that these studies now indicate that certain factors related to bee attractiveness may be readily monitored. In addition to the usefulness of these studies to the plant breeder, It is conceivable that honey production and prosperity of the beekeeping industry could be vastly improved if nectar secretion could be even slightly improved in a few of our major honey plants such as alfalfa or potential honey plants such as soybeans. Again further monitoring of nectar production in breeding programs of such plants would be fully justified and could be of inestimable value in maintain- Ing a prosperous beekeeping industry and an adequate nation-wide force of pollinating bees. I feel that my studies of nectar secretion in cucumbers could be expanded and applied to any crop which is bee- pollinated or a source of honey. CHAPTER II CUCUMBER NECTAR AND ITS SECRETION Watkins (1926) listed cucumber as one of Michigan's important sources of nectar. Edgecombe (19A6) on the other hand mentioned that honey bee colonies placed beside a cucumber field obtained very little honey from it. McGregor and Todd (1952) recorded that with only one colony per 5.7 hectares of cantaloupes, colonies lost weight. Wilson, Moffett, and Harrington (1958) reported that bees collected both nectar and pollen from cucumbers in Colorado. They also concluded that even though large acreages of cucumbers were grown, it was not an important source of nectar. Oertel (1967) reported that cucumber is considered a nectar and pollen plant in all regions of the United States except Alaska and Hawaii. Cucumber nectar is almost colorless, Wilson, Moffett and Harring- ton (1958) and the honey is reported to be light amber or pale yellow in color, Watkins (1926), Milum (19A3) and Wilson, Moffett and Harring- ton (1958). Watkins (1926) described the honey as having a mild and pleasing flavor. Milum (19A3) stated that the honey was strong, later becoming mild, whereas Wilson, Moffett, and Harrington (1958) stated Ithat it did not have an objectionable flavor. Fahn (19A9a, 19A9b) in Palestine found that a single flower of Cucumis sativus secreted a daily average of 3.25 mg of nectar with AA A5 30.7% sugar (dry weight of 1.00 mg), whereas Cucurbita maxima_(WInter Squash) produced 201.25 mg with 16% sugar (dry weight 32.37 mg) and Cucurbita EgEg_(pUmpkin) 98.A0 mg with 28% sugar (27.60 mg dry weight). Vansell (19Ala, 19A2) found that cantaloupe nectar averaged A6% - A6.7% sugar in California and Oregon. Wilson, Moffet and Harrington (1958) In analyzing the honey stomach contents of 18 bees, found cucumber nectar to average A2.2% sugar with a minimum of 37.8% and maximum of A9.2% In Colorado.~ In Wisconsin, Kauffeld and Williams (1972) took 10-20 hand refractometer readings of nectar from the honey stomachs of bees working cucumbers and found the average to be 36% - Al% sugar, depending on weather conditions. Shaw (1953) found the sugar content of nectar from Cucurbita maxima_(WInter Squash) ranged from 18% - 38% with an average of 29.7%. Montgomery (1958) found that Citrullus vulgaris (watermelon) nectar averaged 26.6% sugar and Cucumis EEflfil averaged 31.6% - 32.7% sugar by analyzing honey stomach contents. Clrnu, Tone and Coteanu (1967) found that Cucurbita maxima_flowers secreted from 56 to 558 mg of nectar with a mean sugar concentration of 38%. Even though individual cantaloupe and cucumber flowers secrete nectar abundantly, there are so few flowers per acre in comparison to other major sources, that one would not anticipate that the crop would be an important source of honey. Nectar Secretion of Different Aged Flowers Both staminate and pistillate cucumber flowers secreted most (actively on the first day of anthesis Veprikov (1936) quoting Gorski as A6 cited by Beutler (1953). On the second day only half as much nectar was secreted and on the third day still less. Nemirovich-Danchenko (l96A) found nectar secretion in both staminate and pistillate flowers to be greatest 3-A hours after opening whereas Kaziev and Seidova (1965) reported that cucurbit flowers produced the largest quantity of nectar after the first day of flowering. Bailey, Fieger and Oertel (195A) stressed the importance of considering the age of the flower in nectar work. They found that blossoms of equal age, grown under equal conditions, produced similar quantities of nectar. Blossoms picked at random contained varying quantities of nectar that differed greatly in sugar content. Materials and Methods Plots in which to study the nectar secretion of different aged flowers, were planted on June 7, 1968. Pistillate flowers of the cultivar Piccadilly were sampled from July 23 to August 23. Four dif- ferent aged flower groups were used in this experiment. 1. Flowers 2 days after anthesis 2. Flowers 1 day after anthesis 3. Flowers on the day of anthesis A. Flowers 1 day prior to anthesis, Five bagged flowers were picked from each of the different aged groups each day at l p.m. EST and nectar removed. Results and Discussion The cucumber flower basically has a one day secretion period. INone of the 93 flowers sampled one day prior to anthesis produced any A7 nectar by l p.m. Eighty five per cent of the flowers produced nectar on the day of anthesis and 31% of the day old flowers produced nectar. Only 3% of the two day old flowers contained nectar (Table 1A). Flowers on the day of anthesis produced 1.1 times as much nectar as one day old flowers and 3.8 times that of the two day olds. The one day old flowers averaged only 16.7% sugar compared to 35.A% sugar for flowers on the day of anthesis (Table 1A). The total weight of sugar In the nectar was also greatest on the first day. Flowers on the day of anthesis averaged 2.39 mg of sugar or 2.5 times as much as flowers the day after anthesis and 11.6 times those measured two days after anthesis. The actual weight of sugar present is a preferred indicator since it takes into consideration both the volume of nectar present and its sugar concentra- tion. Since the cucumber flower basically secretes for only one day, factors such as weather or cultural practices that prevent the bees from flying that day, essentially prevent pollination of that days flower out- put. Frult already pollinated, will be one day closer to maturity and gaps in flower pollination will lessen uniformity of pickle production for machine harvest. Further observations have shown that honey bees do not visit flowers the day after anthesis. The Commencement of Nectar Secretion Percival (19A6) reported that the same stimulus which causes the opening of the flower likely stimulates the exudation of nectar from the nectary. Banadyga (19A9) reported that anther dehiscence and nectar A8 .Lmuomc omosooLo Hmcu mLozo.w amo;u co >.co women 0000 .mEmLm....E c. HammoLoxm mezm mo u:0.03 O .mLmu..oLo_E c. oommoLaxo quooc 0o me:.o> 00.0 H_0~.0 00.0 H ..m. 0m.0 H .m.. m m.m .m m.mo;ucm Lmuem m>mo N :..0 H «0.0 mm.. H n.0. 00.0 H m~.m nu n.0m 00 m.mm;ucm Lmuem >00 . mic H and S... H :.mm as H :0 0n 0;... R 285% .6 >3 00.0 00.0 00.0 mm 0.0 mm m.monucm o“ Lo.Le >00 . 20 00". mesm mo Loosm mo 0N.m um Leuooc 0~.m 00< .03 .m><_ N .m>< ..o> .m>< 0.0500 0:.osooLm x 0.0500 .mLmzo.m Lonssoau comm acowam.o c. co.HOLoom Lmuooc mo 00m.Lmosoo 05h I .:. 0.00n 49 secretion in cucumber starts from 17-180C. Shuel (1961) found that anther dehiscence coincided with the beginning of secretion in Streptosolen jamesonii. He was able to show that the period of secret- ing activity of the nectary and stigma coincide. Many plants have a threshold temperature below which they will not begin to secrete, Haupt (1902). This was 80 C for Ergngs_avlgm_ o and 18 C for Prunus laurocerasus and these continue to secrete even if the temperature falls below the threshold temperature, Behlen (1911) cited by Beutler (1953). Wilson (1881) found the threshold temperature for Prunus laurocerasus to be 120 C or greater. Wilson and Haupt are cited from Kenoyer (1916, 1917). Demuth (1923) found that basswood be- gins secreting nectar at 18° C. Materials and Methods In 1969, continuous observations of flowers were started at 6 a.m. EST for 13 mornings to determine the temperature at which nectar secretion began. A centigrade thermometer was placed in a small card- board box and set among the vines so that an accurate temperature read- ing could be recorded. Ten pistillate flowers (MSU 356) were picked each time the temperature increased one degree. The flowers were checked under a dissecting microscope, for nectar exudation and if present, at- tempts were made to collect it. Results and Discussion The previous study showed that a flower one day prior to anthesis did not secrete nectar. This study showed that nectar secre- tion began on the day of anthesis and appeared to be temperature 50 ‘dependent. Below 160 C all nectaries were dry. At 160 C, the nectaries looked moist or wet under the microscope but not with the naked eye. When the temperature was 170 C one or two small beads of nectar formed on the inside of the psitillate flower's cup-shaped nectary. From 180 C to 210 C the percentage of the nectaries containing beads of nectar in- creased as well as the number and size of the beads. The first nectar measurable in a microcap was observed at 210 C and the volume was equal to 0.2% ul. Percival (1946) suggested that the opening of the flower and . commencement of nectar secretion were dependent on the same stimulus. This study would indicate that this is not so. On August 19, 1969, at 6 a.m. at a temperature of 220 C in the field the flowers were closed tight and bees were desperately trying to work them. In breaking the pistillate flowers open, 90% of them contained many large beads of nectar and the staminate flower anthers of SMR 58 were completely dehisced even though the flowers were closed. By 6:30 the sun was beginning to break through the haze. At this time the flowers started to open slowly. My observations during the 13 mornings showed that anther dehiscence started at approximately the same time as the pistillate flower nectaries became moist (160 C) whereas Seaton and Kremer (1939) and Banadyga (19A9) reported that anther dehiscense did not occur until the temperature reached 17 to 180 C. It appears that the commencement of nectar secretion and anther dehiscense are temperature dependent whereas the opening of the flower is at least partially light dependent. 51 Temperature readings from the MSU south farm and tree re- search center which were close to the cucumber plots showed that air temperature may vary within short distances. By using a thermometer within the plant canopy the precise temperature to which the flowers were exposed was obtained. Connor (1969) found that bee flights to cucumbers started at an average temperature of 160 C in East Lansing. Seaton and Kremer (1939) made similar observations. ‘Since the nectary begins to get moist with nectar at 160 C, bee flights are likely associated with an attractive force such as aroma present in the flower at the time of nectar secretion. A Comparison ofiNectar Secretion in Staminate and Pistillate Flowers Fahn (19A9b) reported that the pistillate flower is the chief producer of nectar in the family Cucurbitaceae. He considered the volume of nectary tissue the determining factor and pistillate flowers are larger than staminate flowers. The following data from Fahn shows relative nectar secretion of staminate and-pistillate flowers of cucum- ber, pumpkin and squash. Fresh Nectar in mg Dry Sugar in mg Staminate Pistillate Staminate ’ Pistillate Cucumis sativus 2 h.5 0.5 1.5 Cucurbita pepo 5h.5 102.5 15.0 A0.25 Cucurbita maxima 60.5 302.0 9.75 50.0 Cirnu, Tone and Coteanu (1967) found that the pistillate flowers of Cucurbita maxima secreted more nectar than the staminate flowers. 52 Foster, Levin and McGregor (1965) found that staminate musk- melon flowers (Cucumis mglg) produced .001-.002 ml of nectar whereas hermaphroditic flowers produced .019 ml. McGregor and Todd (1952) found that the sugar concentration of the nectar of staminate canta- loupe flowers was greater than that of pistillate (56:17%). Nemirovich-Danchenko (1960) reported that nectar secretion in both staminate and pistillate cucumber flowers was greatest at 3-0 hours after opening, when pollen was most abundant and bee visitation greatest. The average daily nectar yield was 1.290 t 0.038 mg in pistillate flowers and 0.687 t 0.050 mg in staminate flowers; depending on temperature, it could rise to 2 mg in warm weather. Kaziev and Seidova (1965) found that a pistillate cucumber flower averaged between 1.1 and 2.0 mg of nectar compared to 0.9 and 1.6 mg for a staminate flower, depending on cultivar and environmental conditions. Under excellent conditions pistillate flowers reached 3.3 mg and staminate 2.0 mg. Staminate flowers of cucumbers, melons, and watermelons all secreted a much smaller quantity of nectar than pistillate flowers. Veprikov (1936) reported that staminate flowers on the main stems of cucumber produced 3.1 mg of nectar whereas the pistillate flowers produced only 2.5 mg. 0n the other hand, the pistillate flowers on lateral stems produced 3.0 mg and the staminate flowers only 2.1 mg. Caspary (1808) found more nectar in staminate than in pistillate flowers of several species including Bryonia £12122; (gourd), Cucurbita £222, and Cucumis melo, Kurr (1833) found that pistillate flowers of Bryonia gigi£g_when placed in water, secreted less nectar than similarly treated staminate flowers. Veprikov, Caspary and Kurr were cited by Beutler (1953). S3 Kaziev and Seidova (1965) found that flowers of cucumbers, melons, and watermelons began to secrete nectar between 8-9 a.m. The greatest quantity of nectar accumulated between 11 a.m. and 2 p.m. The sugar content at noon and during the second half of the day was greater than during the morning. In staminate cantaloupe flowers nectar secretion Iceased at 11 a.m. but continued until late afternoon in hermaphroditic flowers. Materials and Methods 1' The‘pistillate flower.--Plants of the cultivar MSU 356 were planted June 7, 1968. Each day, from 7 a.m. to 0 p.m., a minimum of two flowers were picked on the hour from July 26 to August 26. -The nectar was removed for measurement from bagged and caged pistillate flowers. Results Because temperature as well as other weather factors vary from day to day, pistillate flowers began to secrete nectar at different times of the day. On August 12, measurable amounts of nectar did not appear until 1 p.m. whereas on August 20, 21 and 22 all of the flowers sampled were producing nectar at 7 a.m. The number of flowers producing nectar at each hourly interval increased throughout the day until noon (Table 15). For the rest of the afternoon the values were not signifi- cantly different. The average volume of nectar increased throughout the day aver- aging from 1.00 to 9.92 ul. 0n the other hand, the average sugar con- centration decreased throughout the day from 00.5% to 27.0%. The 50 actual weight of sugar increased during the day until 2 p.m., then began to decrease (Table 15). Pistillate flowers produced from 0.0 to 30.15 ul of nectar with a mean of 6.05 ul/day. The sugar concentra- tion of the nectar ranged from 13.6% to 57.1% with a mean of 36.3%. The total weight of sugar in the nectar ranged from .06 to 12.33 mg with a mean of 2.29 mg/day (Table 17). Mean values were based only on those flowers which produced nectar. Materials and Methods 11 The staminate flower.--Flowers of the cultivar SMR 58 were picked daily from August 10 to August 29, 1969. Each day from 7 a.m. to 0 p.m. six caged flowers were picked on the hour and nectar removed. Results During the sampling of pistillate flowers (MSU 350) in 1968, there were five days when the temperature was in the 70's by 6 a.m. Therefore, there was a measurable amount of nectar present.by_7 a.m. During 1969, there were no days when the temperature was high enough to have a measurable amount of nectar by 7 a.m. Therefore, nectar production in staminate flowers in 1969 started later in the day than in pistillate flowers in 1968 (Table 15). Overall, there was an in- crease in the percentage of flowers producing nectar from the time secretion started until noon. For the rest of the day the values were not significantly different. The average volume of nectar increased throughout the day averaging from .73 to 6.79 u1. The average sugar concentration de- creased through the morning from 06.1%.to 03.7% and had a similar 55 .00000: 000:0o:0 0050 00030.0 00000 :0 >.:0 00000 0000 00.0 n.0m 00.0 .- u- is ..000>0 0~.0 H 00.0 00.0 H 0.00 00.0 H 00.0 0m 0.00 :0 00": 0m.0 H 00.m 00.0 H 0.00 00.0 H 00.0 mm 0.00 :0 00am mm.0 H 0~.m 00.0 H 0.0m 00.. H 00.0 00 0..0 .0 00NN ~m.0 H 00.0 00.0 H m.mm 00.0 H .0.0 00 N..0 00 00". 0~.0 H 00.0 00.0 H 0.0m .0.0 H 00.0 .0 0.00 00 :0 0002 0~.0 H 00.0 00.0 H ..0m .0.0 H 00.0 .m a.m0 00 00 .. .~.0 H 00.0 00.0 H 0.00 m0.0 H 00.: 00 0..0 00 00.0. 00.0 H 00.. 00.0 H 0..0 0m.0 H 00.0 m0 0.00 00 00nm ._.0 H 00.0 00.0 H m.~: NN.0 H m0._ .0 0.00 ._. 00H0 0..0 H «0.0 .0.. H 0.:: .~.0 H 00.. mm ..0. 00. :0 00.0 A05. 000:0 00 AN. .ucou A.3v 0~.m c0000: 0N.0 Ahmmv .03 .0000 .0>< c0030 .0>< ..o> .0>< 0.0500 0:.030000 x 0.0500 05.0 .0:0m0:0 00030 00 050.03 .0000 0:0 :o.00:0:00:oo 00000 .00000: 00 05:.o> 00000>0 0:0 0:0 500.0 00 >00 00:.» 0:0 030:0:OLL0 :0000: 0:.0:00:0 0:030.» 000...0m.0 0:0 00 0:00:00 000 I .m. 0.005 56 decline in the afternoon from 07.0% to 00.3%. The actual weight of sugar in the nectar generally increased during the day from .02 to 3.63 mg (Table 16). The flowers had a potential production from 0.0 to 10.88 ul with a mean of 0.01 ul/day. The sugar concentration of the nectar ranged from 27.8% to 60.2% with a mean of 05.3%. The total weight of sugar in the nectar ranged from .09 to 8.36 mg with a mean of 2.23 mg/day (Table 17). Discussion Data showed that pistillate and staminate flowers of pickling cucumbers differ in nectar secretion, though their secreting rhythms are similar. Some flowers do not secrete any nectar and the percentage of both staminate and pistillate flowers starting secretion increased until noon. Without bee visitation, the average volume of nectar and total weight of sugar increased until late afternoon for both types of flowers. The average sugar concentration for both staminate and pistil- late flowers did not significantly change throughout the day. The average mean values for the first day of bloom showed that pistillate flowers produced approximately 1.5 times more nectar than staminate flowers (Tables 15 and 16). The maximum values obtained in the two studies showed an even greater difference, 30.15 ul for the pistillate flowers compared to 10.88 ul for the staminate (Table 17). 'The literature review showed that several other authors found the pistillate cucumber flower to be the predominant producer. Fahn, felt the volume of nectary tissue was the determining factor. Measurements 57 .:0000: 00:0o:0 0000 0:030.» 00000 :0 >.:0 00000 0000 00.0 0.0.. .0... 20:30 00.0 H 00.0 ..0.0 H 0..... 0...0 H 00.0 00 0.00 00 00... 0.0 H .00 .00 H 0..... 00.0 H ..0.0 00 0.00 00 00.0 00.0 H 00.0 00.0 H 0.0.. 00.0 H 00... ..0 0.00 00 00.0 00.0 H 00.0 00.0 H 0.0.. 00.0 H 00.0 00 0.00 00 z. 00.. 0.0 H 3.0 00.0 H 0.0.. 00.0 H 00.0 00 0.00 00 :82 2.0 H 00.. 00.0 H 0.0.. 00.0 H 00.0 00 0.00 00 00:. 2.0 H 0..... .00 H 0..... 00.0 H 00.0 0.. 0.00 00 00.0. 0.0 H 00.. 00.0 H 0.0.. 00.0 H 00.0 .0 0.0.. 00 00.0 0.0 H 2.0 00.0 H .0.. 00.0 H 00.0 0. 0.0. 00 00.0 i... -1 , 1.. 0.. 0.0 0.. x... 00; A05. :0030 00 Afiv .0:00 A.:V 0~.0 :0000: 0N.0 Ah0u. .03 .0000 .0>< :0000 .0>< ..o> .0>< 0.0500 0:.0:00:0 x. 0.0500 05.0 .0:000:0 :0000 00 000.03 .0000 0:0 :o.00:0:00:00 :0000 .:0000: 00 05:.o> 000:0>0 000 0:0 500.0 00 >00 00:.m 000 0:000:o:00 :0000: 0:.0:00:0 0:03o.m 000:.5000 000 00 0:00:00 000 u .0. 0.000 58 .:0000: 00:00:0 0000 0:030.» 00000 :0 >.:0 00000 0000 wm.m mm.0 «.mm 0.00 ww.:. NN.. 00": :N.m 00.0 m.¢m 0.0m w0.0. N~.. 00.0 00.0 00.0 0.00 0..m 00.0. 00.0 00.0 mN.m 00.0 0.0m ..0m ::.N. 00.0 :0 00". 00.0 0..0 «.00 a.mu :~.0. :~.0 :ooz 0~.n 00.0 0.00 w.m~ mm.~. :N.0 00”.. 0..: 00.0 «.00 0..m 00.0 00.0 00.0. 00.0 0:.0 0.0m n.sm :m.w :~.0 00.0 nw.0 :..0 0.00 m..m :4.~ :N.0 ooum in I: In in an in 00.0 0:030.» 000:.5000 00.0 00.0 0.0: m..~ 00.00 .0.. 00.: mm.~. 00.0 m.~m 0.0m ::.~m .m.0 00.0 0:... 00.0 0.0: ..NN 0..:m 0..0 00"~ 00... mN.0 ..w: 0..N mm..m 00.0 20 00". m0.m 00.0 0.00 m.m~ 0:..N 00.0 :002 «0.0 00.0 «.0: 0.0. «0.0. 0..0 00".. m..m ...0 ..mm :.m~ 0~.N. ¢~.0 00.0. 00.0 mm.0 0.0: 0.00 .m.0 :~.0 00.0 :0.~ :..0 w.~: m.m~ 0..0 :N.0 00Hw 0N.N :..0 0.00 0.0m 0..: 4N.0 z< 00.0 0:030.» 000...00.0 A05. A.:. :0030 .03 :0030 .03 :0030 X :0030 x 05:.o> 050.o> Ahmmv 00000.: 000300 00000.: 000300 00000.: 000300 05.h .500.0 »0 >00 00:.» 000 0000000:00 0:030.» :0050000 000:.5000 0:0 000...00.0 :0» :o.00:000 :0000: »o 0.0>0 000 :.00.3 00:.0> »0 00:0: 000 a .0. 0.000 59 reported earlier showed the pistillate flower nectary was l.6-l.9 times wider and had a secreting surface area approximately twice that of the staminate flower nectary. Therefore one would expect the pistillate flower to be capable of greater production. . Staminate flower nectar had a higher average sugar concentra- tion, A5.3% compared to 36.3%, for pistillate flowers, but in total weight of sugar produced the two types of flowers were similar. The pistillate flower averaged 2.29 mg compared to 2.23 mg for the staminate flower. Beutler (l9h9) cited by Ribbands (l953) estimated the weight of sugar secreted per flower per day in major nectar plants ranged between 0.02 mg to 7.6 mg. From these values, the cucumber flower would appear to be intermediate in nectar secreting ability. 'In assess- ing the significance of the crop as a honey producer, we must consider that there are a small number of flowers per acre relative to some plants. Since the cucumber requires insect pollination, it is necessary that the pollinator visit both staminate and pistillate flowers. From an ecological consideration, the pistillate flower produces a greater volume of nectar but the staminate flower produces nectar of higher sugar concentration. Heinrich and Raven (I972) found that the specific amounts of nectar per flower, in terms of calories of food energy are related to the characteristic rates of energy expenditure of the pollin- ator. The honey bee has to visit many more staminate then pistillate flowers to get a load of nectar. But even though there is greater energy expenditure,.the honey bee is about equally rewarded by the staminate 60 flower, because of the higher concentration of sugar. This should help ensure that both pistillate and staminate flowers will be visited. Connor (1969) found the peak activity of honey bees on cucumber flowers to occur at ll a.m. and maximum bee flights in the field extended from 9 a.m. to 2 p.m. These data reinforce Connor's findings in that availability of nectar coincides with bee flights. However, bee visits seem to drop off in late afternoon when nectar should be plentiful. It is possible that nectar replacement after visitation may slow up later in the day or the replaced nectar may become less attractive. Nectar Secretion During the Night Kaziev and Seidova (1965) stated that nectar secretion, in Cucurbitaceae ceased during the night. Kenoyer (l9l6) found that sugar excretion was markedly diminished when photosynthesis stopped because of limited food reserves in the plant. Fahn (l949b) while studying 66 species of plants found that nectar secretion peaked for most in the fore or afternoon, but Capparis slgul§_reached maximum secretion during the night. In some, secretion was low or ceased during the night. Materials and Methods The secreting rhythm of cucumber flowers during the night was investigated by the author during the summer of I970. Caged staminate and pistillate flowers of the cultivar Piccadilly on the day of anthesis were divided into two groups. One half of them were picked and their nectar supply removed at #:30 p.m. The other half were sampled the next morning at 8 a.m. 6l Results Most of the flowers sampled the morning after anthesis were pale yellow and closed. Ninety three per cent of the pistillate flowers and 100 z of the staminate flowers sampled were producing nectar at #:30 p.m. The following morning showed slight decreases, with 87% of the pistillate and 95% of the staminate producing nectar. Comparison of the two sampling times showed that during the night the nectar volume remained about the same. The pistillate flowers average volume decreased from ll.hh to 8.29 ul and the staminate flowers increased from 6.83 to 7.06 ul. The sugar content of the nectar on the other hand showed a drastic change. The average sugar concentration of the pistillate flowers changed from 3h.8% to l2% and in staminate flowers from hl.2% to l8.9% during the night. Decreases were also found in the actual weight of sugar present, from 4.6l to l.3h mg in the pistillate flowers and from 3.30 to l.72 mg in the staminate (Table l8). Pistillate flowers produced approximately 1.68 times more nectar than staminate flowers on the day of anthesis. On the other hand, staminate flowers had a higher sugar concentration, hl.2% compared to 3h.8%. In a previous comparison, pistillate and staminate flowers had similar weights of sugar in their nectar supplies. This study showed that the weight of sugar in the nectar 0f the pistillate flower was approximately l.h.times greater than in the staminate flower. Previously, the pistillate flower was l.03 times greater. 0n the morning after anthesis, the differences were not .as great. Apparently the rates of reabsorption are not equal. Pistillate flcnders contained l.l7 times more nectar and staminate flowers still had 62 a higher sugar concentration, l8.9 compared to 12.0%. Once again the total weight of sugar in the nectar was similar for both. Discussion The literature shows that other researchers have observed losses of sugar from nectar. Bravois (l8hZ) quoted by Beutler (l953) believed that old flowers reabsorbed sugar secreted in nectar. Bonnier (1878) cited by Pedersen, Le Fevre, and wiebe (1958) observed the reabsorption of nectar, if it were not removed from the flower before pollination. Pankratova (1950) found that no reabsorption of nectar occurred in clover florets from which insects were excluded, whereas reabsorption appeared to take place in non-protected florets. Boetius (l9h8) cited by Raw (l953) on the other hand, observed the reabsorption of SUgar and sug- gested that nectar removal might retard the process of reabsorption. Shuel (l96h) was able to show with snapdragon that no reabsorption of water from the nectar took place. Now, direct evidence of reabsorption has been shown. Pedersen g£_gl, (l958) by supplying Clu- labelled sucrose to pollinated alfalfa florets, Ziegler and Luttge (l959) using Clh- labelled glutamic acid on secreting nectaries, Agthe (l95l) by using fluorescent dyes was able to show reabsorption only in old glands and suggested it was related to the general metabolic state of the #5 -plant, Luttge (1962) using 535 and C as tracers and Shuel (l96l) using CIA- sucrose was able to show that reabsorption occurred throughout the secretory period. From the results of this study it appears that the cucumber nectary begins to reabsorb the sugar from its nectar supply and the 63 .:00000 00o:00:0 0000 0:030.» 00000 00 >.0o 00000 0000 0N.0 H ~>.. ._.. 0 0.0. 00.0 H 00.0 00 0:030.» 0000.0000 m..0 H 00.. mm.0 0 0.N. 00.0 H 00.0 mm 0:030.» 000...00.0 .z< oo 0. 0.000000 :00»0 >00 mu.0 H 00.0 00.0 H N..: 00.0 H mw.m .0 0:030.» 0000.5000 00.0 H .0.0 «0.0 H m.:m 00.0 H 0:... >0 0:030.» 000...00.0 .2: om 0. 0.000000 »0 >00 A05. :0030 »o Ax. .0000 A.0V 0~.0 000.03 .0>< :0000 .0>< ..o> .0>< 0.0800 Ahmwv 05.0 .000.0 000 00.:30 0:030.» :0053000 000...00.0 000 0000.0000 0. 00.020: 00.03 :0000 »0 000.03 .0000 000 00.00:0000000 :00:0 .:00000 »0 0E:.0> 000:0>0 00k a .w. 0.00h 64 corolla starts closing during the night after anthesis. At night the sugar supply was diminished by 08% - 7l% depending on the flowers sex (Table I8). The morning after anthesis, pistillate flowers averaged l.3h mg sugar with 87% of the flowers having nectar. A previous study (Table lh) showed that by l p.m. on the day after anthesis, the aver- age weight of sugar had dropped to 0.92 mg with 30.7% of the flowers containing nectar and at the same time 2 days after anthesis only 0.20 mg of sugar remained in 3.3% of the flowers. Pedersen 55:31: (l958) showed that reabsorbed sugar is distribu- ted primarily to growing parts of the plant, such as leaves, flowers and pollen. He showed that sugar was translocated and secreted in flowers that developed later. Ecologically then, even though the cu- cumber flower has only a one day secreting cycle, the flower's sugar supply is still potentially available to the bee at a later time due to reabsorption and resecretion. Connor and Martin (l970) found that delaying pollination to flowers on the 6th and 7th node resulted in . larger pistillate flowers, more ovules per fruit, better shaped fruit and a larger yield. They suggested that stronger root and vine growth vwere responsible. Since the cucumber flower reabsorbs its uncollected sugar supply, through delayed pollination, the plant would be able to build up larger sugar supplies for nectar production through a longer period of photosynthesis and reabsorption before collection. Also tfl1rough delayed pollination, larger flowers would provide larger volumes cyf nectar with more sugar as was pointed out by the positive correla- tions found in Chapter I. 65 As previously stated, the maximum nectar production for a staminate flower was lh.88 ul found in the cultivar SMR 58 (Table l7). In this study, staminate flowers of the cultivar Piccadilly produced a maximum of l7.07 ul, indicating that sufficient levels of nectar produc- tion were maintained in the development of this cultivar. Comparison of Nectar Secretion in Different Cucumber Cultivars Kaziev and Seidova (l965) stated that the range of values for nectar secretion in staminate and pistillate cucumber flowers depended to some extent upon the cultivar and environmental conditions. Materials and Methods Two plantings of eight different seed lots including six culti- vars were studied during the l968 summer. Each planting contained l0 plants from each seed lot. Flowers were picked from the first plant- ing at 7:30 a.m. and from the second at l:30 p.m. As time allowed, nectar was removed and analyzed. The eight seed lots used were: a. Spartan 27 b. Spartan Dawn - no pollinator c. Piccadilly - Med l, no pollinator d. Piccadilly - Med ll, no pollinator e. Spartan Progress- (MSU 350 x 38l) f. MSU 350 g. Piccadilly - Med ll, with pollinator H. SMR 58. 66 Results Comparison of nectar yields of different cultivars was compli- cated by their different production of staminate and pistillate flowers but the data was used to reinforce the knowledge of these differences. Spartan Progress and MSU 350 rated highest in nectar production while SMR 58 and Spartan 27 rated lowest when samples included nectar from both staminate and pistillate flowers (Table l9). Both Spartan Progress and MSU 350 are gynoecious cultivars, whereas SMR 58 and Spartan 27 are monoecious, producing predominantly staminate flowers. SMR 58 and Spartan 27 averaged from 3-h ul of nectar per flower compared to 7-9 ul for the top producers. The commercial gynoecious hybrids which produce more pistillate than staminate flowers rated between the above two extremes in nectar production. The rankings were somewhat reversed for sugar concentration (Table l9) since staminate flowers produced nectar of a higher concen- tration than pistillate flowers. SMR 58 was highest averaging 00.9% sugar and MSU 350 lowest averaging 3h.3%. SMR 58 produced no pistillate flowers and MSU 356 no staminate flowers during the sampling period. Spartan Progress and MSU 350 rated high in total sugar production aver- aging over 0 mg per flower with SMR 58 and Spartan 27 at the bottom with less than 2 mg per flower. However, the large differences in nectar production, sugar con- centration and total weight of sugar present may not be due to differ- ences between cultivars but rather differences in staminate and pistil- late flower production. Earlier in the chapter, i found that the pistillate flowers produced approximately l.5 - l.7 times more nectar 67 m_.o 0 mm._ 0 0.0 0 0.0m m:.o 0 00.0 an RN cmgtmam ._.o 0 00.. _ o._ 0 m.o: 00.0 0 0a.: 00 mm 020 00.0 0 ~m.~ m 0.. 0 ...m m0.o 0 _:.m mN _ am: >___cmuu_: _m.o 0 mm.~ m 0.. 0 ..Nm om.o 0 00.0 00 __ vmz >___umuu.0 00.0 0 .0.0 . m.o 0 0.0m ~0.o 0 00.0 _m 0200 cmutmam .0.0 0 00.0 N 0.. 0 ..o: 00.. 0 00.0 0. :00mc___oa\__ um: >___umuu_0 om.o 0 0..: 0 m._ 0 m.:m 00.. 0 00.. .. omm :0: 0m... 0 0.0.: N 0.. 0 ..o: .00.. .0 .00 on 00809.: 03:80 A05. :0000 :0000 :0MWMW »o 0N.0 00. 0000 »o .03 .0>< 0000 X .0>< ..o> .0>< 0.0000 .A 00.000.0 00a 0 0:0>.0.0o 0:0.:0> »o 000. 0000 000:0»».0 000.0 »0 0:030.» 50:» :00000 0. 00000:0 :0000 »0 000.03 .0000 000 00.00:0000000 :0000 .0E:.o> 000:0>0 000 I .0. 0.000 68 than the staminate flower. Therefore, differences in flowering pattern and sex ratio between cultivars could result in erroneous conclusions. By separating data on the two types of flowers, it was again found that pistillate flowers averaged more nectar per flower than stam- inate (Table 20). The pistillate flowers of the second planting aver- aged from 7.31-10.67 ul and the staminate flowers from 2.h8-5.02 ul. Overall the pistillate flowers of the second planting averaged 9.02 ul compared to 3.88 ul for the staminate, or the pistillate flowers pro- duced 2.3 times more nectar. The pistillate flowers of the first planting averaged from 1.61-3.39 ul whereas the staminate flowers aver- aged l.28-l.66 ul. Overall, for the planting staminate flowers averaged 1.50 ul and pistillate flowers 2.7“. From these values, the pistillate flowers produced approximately 1.8 times more nectar. All previous studies showed that staminate flowers produced nectar of a higher sugar concentration. But in the first planting, staminate flowers overall, averaged 41.9% and the pistillate flowers 03.0% sugar (Table 21). However, the differences were not significant. All staminate flower groups of planting two contained a higher sugar concentration than similar groups of pistillate flowers. In the plant- ing overall, the staminate flowers averaged 40.2% sugar and the pistil- late flowers 33.9%. In both plantings the average total weight of sugars present in the nectar of pistillate flowers was greater than staminate flowers. (Table 22). Staminate flowers averaged from 0.66-0.79 mg whereas pistillate flowers contained 0.82-l.72 mg in planting one. Overall the 69 0:030.» 02 In 00.0 H 00.: 0N 00.0 H 00.N 0. .0.0 H 00.. 0m 00 020 :0000...00 30 0 3.0. 0 00.0 0. 00.: m i... 0 00.0 0: mm... 0 00.. : \: B: 3:28: 00.. H 00.0 0. 0:030.» oz in m..0 H 0~.~ 00 0:030.» 02 in 000 00: :0.. H .0.0 cm 0:030.» 02 ii m~.0 H 00.~ 00 0:030.» 02 :1 000:0o:0 000:000 00.0 0 0.0.0 m 8.0 0 8.... .N 3.0 0 mm.m o: a... 0. om. _N : B: 3:38: .0.. H 00.0 N. ~0.0 H 00.0 0. :m.0 H 0..m 00 00.0 H 00.. 0. _ 00: >...0000.0 00.0 H 00.0. N. ::.o H ~0.: 0. .0.0 H 0..m o0 :~.0 H «0.. .. 0300 000:000 m:.~ H .0.0 : N~.0 H 0:.N mu 0~.0 H .0.. .N .0.0 H 00.. 0m 0m 000:000 ...0 :3 :3 :3 0:030.» 0~.0 0:030.» 00.0 0:030.» 0N.0 0:030.» 0N.0 00. 0000 000...00.0 0.0500 0000.5000 0.0000 000...00.0 0.0000 0000.5000 0.0500 . m00000.0 00m 0 . m0.000.0 00. . .0:0>.0.:o 0:0.:0> »o 000. 0000 000:0»».0 000.0 20:» 0:030.» 000...00.0 000 0000.0000 >0 00o:00:0 :00000 »0 0E:.o> 000:0>0 000 u .00 0.000 70 00030.0 oz --- 0.. H 0.0: 0N m0.o H o.m: 0. 00.0 H ~.:: 00 mm 020 . 0000:...00 0.0 H 0.0m H 0.. H 0.~¢ m .0.0 H 0.:: N: 00.. H 0.0: __ \__ Ho: >___Hmoo_0 0.. H m.:m N. 00020.0 oz --- 00.0 H ..m: mm 00020.0 oz --- 00m :0: 0.. H ..o: om 00030.» 02 nun m:.o H :.m: n0 00030.» 02 nun 0000m000 c00000m 0.0 H m.~m m 0.0 H 0.0m OH 00.0 H ..Na mm 00.. H 0.0: _N __ um: >___Hmuu_0 m.— H ..mm N. 0.0 H 0.0: 0. 00.0 H ..00 om 00.. H o.~¢ m. . 002 >___nmuo_0 _.. H ~._m N. 0.0 H ..mm m. .0.0 H m._q mm 00.. H 0.0: o. :200 cmu0mam ~.m H 0.0N m 0.0 H 0.0: mm 00.0 H m.m: ON -.~ H m.mm mm KN c000000 .00 .00 .00 .00 00030.» 0N.0 00030.» 0N.0 00030.» 0N_0 00030.» 0N_0 uo. 000m 000...00.0 0.0500 0H0c.E0Hm 0.050m 000...00.0 0.0Emm 000:.5000 0.0E0m 0:00cm_0 0cm . 0:00:0_0 00. 0 500» 00030.» 000...00.0 0:0 000:.Emu0 >0 .000>.H.:u 0:0.00> »0 000. 0000 0:000»»_0 000.0 00030000 00000: »0 00.000H000c00 00m00 00000>0 00» u ..N 0.00H 7| 00030.0 oz -- 0..o H :0.. mN -.o H 0... 0. ...o H :0.0 mm 00 0:0 0000:...00 No.. H mm.m N 0N.o H mo.N m m..o H mm.. N: ON.o H m>.o .. \.. 00x >...0000.0 00.0 H N..: N. 00030.» 02 nu mo.o H m... mm 00030.» 02 nu omm :0: mm.o H o:.: Om 00030.» 02 I: N..o H m:.. no 00030.» 02 In 0000m000 0000000 :N.. H MN.m m mN.o H mm.N 0N m..o H N>.. mm mo.o H mw.o .N .. 002 >...0000.0 om.o H .>.N N. mN.o H mm.. 0. :..o H m:.. om ...o H m>.o w. . 00x >...0000.0 mm.o H om.m N. 0N.o H om.. m. :..o H m:.. mm ...o H 00.o o. 0300 0000000 0~.o H m..m m ...o H m... 00 m..o H 00.0 cm ...0 H 00.0 N0 RN 0000000 Ame. AmEV Ame. Ame. 00030.» 0~_0 00030.» 0~.0 00030.» 0N.0 00030.» 0N.0 00. 0000 000...00.0 0.0600 000:.5000 0.0500 000...00.0 0.0500 0000.5000 0.0500 000000.0 HCN 00.000.0 00. 00030.» .000>.u.:0 0:0.00> »o 000. 0000 0:000»».0 000.0 200» 000...00.0 0:0 000:.5000 000 >0 00030000 00000: 000 c. 0030» 00030 »0 00m.03 00000>0 00h : .NN 0.00% 72 staminate flowers averaged 0.72 mg compared to 1.35 for pistillate flowers or l.9 times more sugar. The nectar of pistillate flowers of planting two contained l.9 times more sugar than that of staminate flowers. The pistillate flowers averaged 3.62 mg compared to l.89 for the staminate flowers. Discussion There were no significant intervarietal differences in nectar secretion between staminate and pistillate flowers. In selecting culti- vars for attractiveness to bees the plant breeder needs to be aware that staminate and pistillate flowers differ in their nectar secreting characteristics. The relative numbers of staminate and pistillate flowers produced by different cultivars may affect their attractive- ness to bees due to variations in their available nectar supply. In general there would be concern with keeping staminate and pistillate flowers equally attractive so as to ensure cross pollination. There must of course be a balance between the numbers of pistillate and staminate flowers to ensure enough pollen to do the job without having bees spend excess time on staminate, non-reproductive flowers, Connor and Martin (197]). Currently, commercial seed companies mix l0% - l5% seed of monoecious lines with gynoecious hybrids to insure a sufficient supply of cucumber pollen. If nectar supplies of the two cultivars being mixed were significantly different in attractiveness, the honey bees might fail to cross over. However, at the present time, no reports have been received or observations made of cultivars that appear to be un- attractive to the honey bee. Any significant increases in quantity or 73 quality of nectar produced, by cucumbers would help to lessen the competi- tion that exists between cucumbers and other nearby nectar sources Colli- son-and Martin (I970). The Influence of Flower Position on Nectar Secretion Kaziev and Seidova (1965) found that flowers of all species of Cucurbitaceae located at or near the base of the main stem secreted be- tween 12% - 2l% more nectar than flowers located on lateral stems. Veprikov (1936) cited by Beutler (1953) reported that staminate flowers on the main stem of cucumber produced more nectar than those on the lateral stems. The opposite results were found for pistillate flowers. Materials and Methods During the summer of l968 three studies were done involving flower position and nectar secretion. 12§§53--Eight different seed lots were used in the experiment, l0 plants for each. The flowers were picked at 7:30 a.m., nodes recorded and nectar removed. The eight seedlots used were: a. Spartan 27 b. Spartan Dawn - no pollinator c. Piccadilly - Med i, no pollinator d. {Piccadilly - Med ll, no pollinator 'e. Spartan Progress (MSU 356 x 381) f. MSU 356 g. Piccadilly - Med ll, with pollinator h. SMR 58. 7h l9688.--A second planting of the above seed lots was made later in the summer. Five plants from each of the cultivars f, g and h grew upward on cane pole stakes within a cage and the flowers were harvested at 9:30 a.m. The node of the flower was recorded and nectar removed. l968C.--Using similar plants grown on the ground flowers were picked at l:30 p.m.; sorted by seed lot, main vine or lateral and nectar removed. Results 12§§A,--Since the flowers were sampled at 7:30 a.m. nectar secre- tion was just getting under way. Staminate flowers produced 4.2 times more nectar and pistillate flowers 2.l times more on lateral vines than on main vines (Table 23). Sugar concentration of the nectar of pistillate flowers was not significantly different between the main and lateral vines. Staminate flowers on lateral vines showed a higher concentration than those on the main vines, 45.0% compared to hl.h%. These differences are reflected in the total weight of sugar present since both volume of nectar and sugar concentration are involved. Both staminate and pistillate flowers on the main vine contained more sugar than those on lateral vines; the staminate 1.8 times more and pistillate 1.6 times more. To look for further trends, the data were sorted by sex and node position. Tables 2h and 25 show that there is a tendency towards slight increases in flower size, nectary size and volume of nectar further down the vine from the base of the plant. Differences in sugar concentration 75 and total weight of sugar present were not significant. Staminate flower averages ranged from 37.9 to 43.9 mm wide, averaging overall 40.6 mm compared to a range of 42.9 to Sl.0 mm and a mean of 47.9 for pistil- late flowers. In both cases node one had the smallest flowers and node two the second smallest. Differences in nectary size were not as large. The staminate flower nectaries averaged from 2.4 to 2.9 mm with an over- all mean of 2.6 mm. On the other hand, the nectaries of pistillate flowers averaged from 4.l-4.6 mm with an overall mean of 4.4 mm. Nectar production of staminate flowers averaged from l.47-2.l8 ul and 3.0l-5.27 for pistillate flowers. Overall mean for staminate flowers was l.8 ul and 3.9 for pistillate ones. The average sugar con- centration for staminate flowers ranged from 37.3% to 4l.8% and pistil- late flowers fluctuated from 37.8% to 44.4%. Likewise the total weight of sugar fluctuated from 0.68-0.90 mg for staminate flowers and l.44- 2.27 mg for pistillate flowers. Within this study, overall the pistillate flower was larger, the nectary was 1.7 times wider, produced 2.2 times more nectar of a higher sugar concentration and it contained 2.2 times more sugar than the staminate flower. 12§§§3--The three cultivars used had completely different flower- ing patterns. MSU 356 produced only 49 pistillate flowers. Piccadilly l58 staminate, l7 pistillate, and SMR 58, 265 staminate and ll pistillate. Besides genetic differences in the staminate-pistillate flower ratio, basically only one pistillate flower was produced at each node, whereas several staminate flowers were produced at each node. Since the 76 00.0 H 00.. Nm.o H o.m: .0 m..o H Nm.. mm 000.> .000000 00.0 H mm.. :m.o H w.N: MNN ...o H 00.0 mNN 00.> 0.02 00030.» 000...00.0 wo.o H N:.o mw.o H o.m: N. N..o H m>.o 0N 000.> .000000 mm... H £5 E... H 00.3 om mo... H 0.... 00 90> 502 00030.» 0000.5000 A0EV 00030 »0 AX. .0000 0N.0 A.3v 0N.0 00.0.000 000.03 .0>< 00030 .0>< 0.0500 ..o> .0>< 0.0500 0030.0 .A .00000. 000 0.05 00 000000. 00030.» 00053030 000...00.0 000 0000.50H0 >0 00030000 00030 »0 000.03 .0000 000 00.0000000000 00030 .000000 »0 0&3.o> 00000>0 000 »o 000.000500 < n .MN 0.00H 77 staminate-pistillate flower ratio varied greatly between the cultivars,- the data were sorted by flower sex. Due to the small number of pistil- late flowers produced, the data for nodes l-4, 5-8 etc., were combined (Table 25). Even the lumping of data for the pistillate flowers shows no significant trends (Table 25). Likewise no significant trends were found for staminate flowers (Table 24), though at times it appeared that petal size, nectary size, volume of nectar and total weight of sugar gradually increased further from the plant base. The overall means (Tables 24 a 25) show that pistillate flowers were larger, contained a wider nectary that produced a larger quantity of nectar which contained more sugar than staminate flowers. The only difference from the l968A study was that staminate flowers contained a higher sugar concentration, 45.6% compared to 42.0%. This is in agree- ment with earlier resuls in Chapter II where staminate and pistillate flowers were compared. 12§§£:--After sorting the data of the eight seed lots that pro- duced flowers on both main and lateral vines, analysis showed that all seven had a larger volume of nectar in flowers on.the lateral vines than on the main vines (Table 26).’ Flowers on lateral vines of cultivars Spartan Progress and MSU 356 produced significantly more nectar than (other seed lots tested. Spartan Progress averaged l6.42 ul and MSU 356, l5.74 compared to 9.64 ul or less for the rest. Six of the seven seed lots had a lower per cent sugar in the lateral flowers but a larger amount of sugar. These can only be used as trends since the flowers Table 24. - Effect of node posi ion on flower size, nectary size and nectar secretion of staminate cucumber flowers. Avg. wt.of sugar (mg) Avg. % sugar N Avg. vol. 00 (mm) Avg. nectary SIze N (mm) Avg. flower SIze N Node 4w—Ln '—O'—N c>c>c>c> HH+I+I :omoo h:oxa>u> COCO LnNON cocoon COO—u— 'H‘H'H'H MUN-Aw scoo— mafia-4r 4'\O--l\ MF4‘LA 6666 'H‘H +4 4" now— :o—m mfimm NF. m—NN o—I-I-u—N 6006 HHHH 4'4'\OO\ NNNN --NM4' l 68 B r~uxq>oxux —-—-oIc>an I I I c>c>c>c>c>c>c>c>c>c> +I+l+i+l+l+l+l-l-l-i-l-l-C-l-l-l-l-i-I-l-l-H-I-l-i-O oxmnixocaaacaqu>r~u>0\«n0-—cn-: C)OlC>—-"\4rU\u3h»c)—-u\——__\oln.. —NN—-NN —————————N— mmmoxomomnoonmxomom m\DO\LA\O\O\O\Dl\U\CDNwU\O4'O\ 06666666666466640 HHHHHHHHHHHHHHHHH O\O'— 4§m\0i\.N®OMO\—\OO\4‘ LnLn JJSmJan N006 :rd' JJJJJJJJ ##4## M—MFNme—w—Nw— 4'0 NNNNNNNNM—N4’O4INM 00000000000000 DO -l-|-l-|-l-I-i-|+|-l-l‘H-l-I-l-I-l-|+l-i-'-l-i+l-H-i-|-i-I moooommJ-oommonimmm: 00wONLfiLnONmo—N mmmm NN—NNNNMMNMMMMNJM OONwmmNN :4ommwMN—NN:: [\memo—v-wo—oommmomo c>c>c>c>c>cac>c>c>c>c>c>c>c>c>c>c>c>c> HHHHHHHHHHHHHHHHHHHH c>—-«wawnin:-¢-¢-¢\O-¢¢0——cncnstcocntn oIoIoInIoIoIoIoIoIoIoIoI ;2 a—oorxooxoxomo MMNNNNN oommmNMN—Ixono Ln—Noommoxm-—:r\o H+I+I+I+IH+IH+IHHH <3xo— \OLneuuaoxh~h~h~c> 4'ChNowOChO [\v—NN mmd'd'md'mgmd'0'4 —\Ocl: ”04' [\O -- (NW NNN F-Nm4'Ln\Ol\wC\ 15 18 l4 l0 ll l2 NNNNNNNN mOM4—LfiMN — moom— oooo ON—anNOC I F-M—4'M4'M HH+IH-H+I+I+I uxanr~aauxc>c>c> ONNO N——4'3 <01 Avg. % sugar 00 Avg. vol. N Avg. nectary SIze (mm) Avg. flower N size (mm) N Node l 68 A 'meo 79 \OMd’Jm—ON—Jdbm PF—FO—NNMJU‘MN ”00000000000 HHHHHHHflflHHH ._j N—w 61305500 ".999?5€9N99 O—mmm—NmoNLfiN #—\Owl\.—'-:JMI\ Nd) ——00000M—'—N0 +I+I+I+I+I-H+I-H+I-l-I+I-I-I «aaaan4ruxr:u\a>:ruxoon $535533m353? M O‘MO‘H-O OMNM m anN‘DU‘ . N000000—:0'—00 +I-i—l-l-I+I+l-H+l+l-H+I‘H-H P—NmNJmN—Nwm 0‘0!\.\O'—:N\ONO\®MM MMMMJJMMMJMM NNJNomd'J'MLnxorx commonal— meWNI—F’NMNkDN —'0000'—'—'—'N'—NN C>C>C>C>C>C>C>C>C>C>C>C> Hflflflflflflfifififlfl m—mmaamomJ—m 355535555555 [\41' 0WD LnONNO 0 [\v-LAMN -- QNQN —--—a\~+-—\o O\ Nxomxoxommoxooomm —-C>C>C>C>C>—-OlOl—-—-ol Hwfiflflfififlflflfi+l a\h~a\h~aquanICIO\u\—- N comoonIxxo—ooooo 4’ #:JJJde-m: 1968 B t ‘t t ‘t wQMO mmd'l-n CICICICI flflflfl MJ'P‘F— F-NN oor~ arrs cnxo cuxo 55555 +I+I+I+I+I “595m [\Nmm: ##JJM 3 l4 25 17 3 5-8 9-ll l3-l6 ]. l7-20 l.75 t 0.3l 42.0 t l.52 3.18 t 0.45 4.l t 0.07 42.9 t 2.33 Overall means Table 26. - Comparison of main and lateral vine flower posi ion on nectar secretion of eight different seed lots (1968 C). H 3 —»-~ mm tSJi 4.) I. '0 0'10) >3 c> +I-H om NM NN mm mN o— +|+| LN" RN mm +n+n Spartan Dawn ON ML“ c>c> +|+I \o— "-0 NM [\4’ 4’0 _— +l +l NN o — +I+l 4'\O mm J'lN Z_.l Piccadilly Med 1 80 LAM 00 -—m ‘H'H NI— mm —0 (DB ON +|+I -— -H+I «\oa mm mm +I+| 2.4 MSU 356 2.6] t 0.h8 40.6 t 1.61 6.10 1» 1.42 15 Piccadilly/pollinator \o\o —-c> c5.l ‘H'H r~r~ v—N MO +I+| c>r~ —Io§ #m SMR 58 8] o a 4 mo._ « No.~ om._ + u.mm mm._ a _m.m N m A --- --- --- o a z o_.o a hm._ mo._ w o._: mm.o « Nm.m mu m 2 mm mzm --- --- --- _ a A --- --- --- o m 4 mo._ a m:.m :_.m w :.~m m_.m a m_.m o a z toumcw__oa m~.o a mo.~ m:._ a m.~: mm.o a mo.: m m z \__ cm: >___uouu_¢ om._ « mu.“ om.o H «.mm :m.m « :N.m_ N a 4 --- --- --- o m A mn.o « mm.m mm._ a m.mm Nm._ a um.m m. a z --- --- --- o m z omm 3m: mm.o H mm.m 04.. « m.mm mm._ a «a.m. m a 4 --- --- --- o m A mm.o a :m.m o... a «._a No.0 H m~.w :N a 2 an: in: II: c m z mmocmoLm cmucmam o~._ H mm.: mm.. a a.mN _m.a « mo.m_ N a A o~.o « Nw.u mo.m a a.mm N_.o a -.m N m 4 mm._ a m:.~ m~.m a N.:m no.0 « em.“ m m z m~.o a om.~ m~._ « m.mm mm.o « mm.: m. m z __ um: >___umou_m mm.o « m_.m m~._ a m.¢m ~N.N « N_.w : a 4 --- --- --- _ m 4 o~.o m m:.~ m~.~ « ~.~m :~.~ « mm.“ m m z :~.o + mm._ mm.o « m.o: :m.o a mm.m m_ m z _ um: >___umuu_m £5 a min 8.. « Em 2.0 m m; m n. 4 m:.o « ::._ :N._ m m.Nm m... + om.m : m 4 :m.o « -.: am._ w :.~m -._ H NM... m a z -.o a. 3.. mod + m.mm wad m 9.: m_ m z :38 53.6% -.o « m_.m m_.m « m.m~ m:.~ + mm.“ a a 4 _m.o « m~._ om._ « a.mm no._ a mm.m : m 4 --- --- --- o a z mo.o « o... em.o « awom, N_.o « m~.~ SN m .z HMN smegmam Amav meam .pz cmmzm oN_m Ho. comm _mu0u .m>< & .m>< ._o> .m>< .o_aEmm xom co_u_mom .Au mom_v moo. ummm “cotmcc_u u;m_o co moc_> _mcmum_ cam c_mE osu co vaumoo_ mcozo_m Lucasozo mum—._um_a cam oumc_Emum mo cOm_Lmaeou I .NN «peak 82 were not sorted by sex and the sample sizes of the lateral flowers were rather small.» Comparison of cultivars that produced staminate and pistillate flowers on both lateral and main vines showed that staminate flowers on lateral vines produced more nectar than those on main vines h out of 5 times. Similar findings for pistillate flowers were found 5 out of 6 times (Table 27). The concentration of sugar from the nectar of stam- inate flowers on the main stem was greater than that on lateral stems 3 out of h times. Pistillate flowers on the main stem had a higher concentration 3 out of 5 times. As a result, the total weight of sugar in the nectar of staminate flowers on lateral vines was greater 3 out of h times and for pistillate flowers it was greater 5 out of 6 times. Pistillate flowers produced a larger quantity of nectar than staminate flowers on both the lateral and main vines. Likewise, in both positions staminate flowers contained a higher concentration of sugar than pistillate. The nectar of pistillate flowers contained a higher weight of sugar than staminate flowers in similar locations. Discussion Studying the association of nectar secretion with position of the flower on the stem proved to be difficult because the various culti- vars differ greatly in the number and sequence of staminate and pistil- late flowers produced. Some of the new hybrids produced only pistillate flowers. Basically only one pistillate flower is produced at each node, whereas several staminate flowers are produced at each node on the same day or more often on different days. Therefore, sampling data were 83 affected by unavoidable differences due to weather, carbohydrate supply, vine age, etc. With the flowering pattern peculiar to staminate flowers you might have an older vine with staminate flowers on nodes 3,8,]2,l8 and 2l all on one day, whereas pistillate flower production would be on node 24 only.) Flowers on lateral vines tended to produce a larger quantity of nectar containing a higher weight of sugar than those on the main vine. This may be explained by the relative length of vascular tissue leading to the flowers sampled. Connor (1969) found that fruits from a higher node position, and thus older plants contained more seeds and were longer than fruits from lower nodes (i.e., younger plants). He also found the effect of node position was most noticeable in highly gynoecious varieties. His results indicated that pistillate flowers found on the early nodes were smaller, had smaller ovaries with less ovules and developed into shorter fruits, often misshapen. As a result, Connor and Martin (l970) pro- posed delayed pollination. Their studies have shown that a delay up to ll days after the first appearance of pistillate flowers resulted in higher yields of cucumbers with a greater dollar value. My studies, (Tables 2h 8 25) show that there tends to be slight increases in flower size, nectary size and volume of nectar as you move down the vine away from the base. With the positive correlations found in Chapter I relating to: (l) nectary size and volume of nectar, (2) nectary size and actual weight of sugar in the nectar, (3) nectary size and ovary length and (h) nectary size and petal size, by delaying pollination the 8h bees should be visiting larger flowers, which in turn offer larger quantities of nectar with more sugar. This makes the flowers more attractive to the bees and through pollination, the grower should have a higher yield with a greater dollar value. Not only will the flowers' nectar supply be more attractive, but there will be a larger number of flowers per acre which is advantageous to the bees. Also, as was sug- gested earlier in the chapter, nectar not collected during the waiting period before bees become active, may be reabsorbed and resecreted at a later time. This may allow the plant to increase its stored carbo- hydrate supply and favorably affect nectar secretion. CHAPTER III THE NECTAR SECRETION CYCLE AND HOW IT IS AFFECTED BY HONEY BEE VISITS AND THE PROCESS OF FERTILIZATION Honey bee pollination has been recognized as necessary for normal cucumber production by several authors. The flower's nectar supply ap- pears to be the primary attractant since very few honey bees have been observed packing pollen pellets in the corbiculae; those observed being small in size compared to the pellets from major pollen sources. Bohn and Mann (I960) found that a nectarless strain of muskmelon was not visited by bees; therefore, nectar may be the primary attractant in Cucumis me_l_o_. A honey bee seldom returns to a flower that it recently visited. When this does occur, the bee leaves immediately for another flower, ap- parently sensing a prior visit. In following bees, I have noticed that the honey bee tends to work a group of flowers in a small area. Then it starts moving around a great deal, just visiting a flower now and then. It would appear that the honey bee has nearly a full load of nectar and visits a few flowers at random before returning to the hive. The honey bee in removing nectar from a pistillate flower gener- ally inserts and withdraws her proboscis 2-3 times. She inserts her proboscis at the periphery of the stigma, between the lobes, to reach the cup-shaped nectary below (Fig. 20). The cup generally holds the 85 86 entire nectar supply since secretion only takes place on the inner surface (Chapter I). Occasionally, through lack of visitation, the cup becomes full, spills over the sides and nectar collects betWeen the corolla wall and the nectary. In moving around the stigma and inserting her proboscis, the bee keeps her hind legs on the corolla. As she moves, the hind legs step from petal to petal (Fig. 20). In order to reach the nectar of a staminate flower, the bee in- serts her proboscis between the central mass of five anther lobes and the wall of the corolla. The anthers are attached to the wall of the corolla, providing an obstacle to a bee trying to get nectar from the flower. In addition the nectar encircles the nectary at its base and is found between the nectary and the corolla wall, thus forcing the bee to move around the anthers several times, inserting and withdrawing her proboscis. Occasionally, in attempting to visit a flower, the bee is confronted with competition, such as another bee, a cucumber beetle or syrphid fly. When confronted with a beetle or fly, the honey bee moves away to another flower. If a honey bee lands on a flower being‘ worked by another honey bee, the working bee is generally chased away. Nectar Removal by the Honey_Bee Meyerhoff (l958) in studying bee visitation to inner and outer nectaries of rape, concluded that bees are unable to distinguish empty nectaries from full ones. Park (l95h) came to a similar conclusion.' Pk: suggested that the bee can only tell by inserting her proboscis and. inhen nectar is found, she remains to suck until all nectar within reach (IF her proboscis has been taken up. 87 Materials and Methods Bagged pistillate flowers of the cultivar MSU 356 were sampled in the afternoon on the day of anthesis during the summer of l969. Some of the flowers were unbagged and one honey bee was allowed to visit each flower. Immediately after the visit, the flower was picked and the nectar that remained was removed. The remaining unvisited flowers served as controls. They were picked and the nectar collected to determine ap- proximately how much nectar the honey bee removed. Results In the 25 recorded visits, honey bees removed all the nectar present with one visit (Table 28). The small number of controls sub- stantiated that the flowers contained nectar prior to visitation. Honey bees averaged 60.] seconds in their initial visit and removed a mean of 9.64 ul of nectar. Discussion 'Connor (1969) found that honey bees averaged 36.2 seconds on their first visit to cucumber flowers. He also noted that the duration of a first visit to a flower varied with the time of day of the visit. For l2-l p.m. first visits lasted 39.9 - 43.] seconds, l-2 p.m. 37.3 - 37.l seconds and from 2-3 p.m. 37.9 - 38.3 seconds. These values are lower than reported here, since his values included both staminate and pistillate flowers. Honey bees constantly revisit cucumber flowers throughout the day; therefore, the cucumber flower must resecrete nectar fairly rapidly after each visit. If it were not for this replacement of nectar, the 88 Table 28. - The amount of nectar removed from a pistillate flower in one visit. Time Spent Measurable amount Controls - Date in one visit remaining vol. of nectar (ul) 8/20/69 55 0.00 (3:30 - #:30) 67 0.00 50 0.00 No Controls 59 0.00 Measured 66 0.00 8/28/69 llO 0.00 l#.h0 (3:00 - #:00) llO 0.00 8.5h 40 0.00 l2.20 35 0.00 6.83 #0 0.00 19.52 65 0.00 l3.9l 75 0.00 I3.9l 55 0.00 -- 9/4/69 us o.oo 6.3h 40 0.00 5.85 (2 OO) 50 0.00 h.15 32 0.00 ~- 3h 0.00 -- 9/5/69 l05 0.00 6.83 95 0.00 3.l7 (3:00) 85 0.00 -- 75 0.00 -- 50 0.00 -- 25 0.00 -- Overall mean 60.l f 5.0 9.6h t l.h5 89 flowers would become unattractive to bees soon after anthesis, since the nectar supply is the primary attractant. The Rate of Nectar Replacement after Removal That removal of nectar by bees and other nectar gathering in- sects may increase nectar secretion was suggested by Free (I970), Koresh- kov (I967), and Wykes (I950). Melnichenko (I963) found that multiple bee visits normally increased nectar productivity of flowers by 50% - 75%. Bogoyavlenskii and Kovarskaya (I956) cited by Free (I970) and Maksymiuk (l958), reported that flowers from which nectar was removed three times per day produced more sugar than those from which it was removed once a day. Raw (I953) found that artificial removal of nectar Increased the amounts of nectar and sugar secreted, but the average sugar concentration of the nectar was markedly lowered. He suggested this might be due to differences in the osmotic relations of the nectary tissues and secreted nectar. Wykes (l9l5a) had similar findings. The sugar concentration of nectar in flowers visited by bees was lower than in those protected from bees according to Pedersen and Todd (l9h9) in alfalfa. Pedersen (l953b) showed that the use of heavy concentrations of bees had a tendency to reduce the sugar concentration. Meyerhoff (l958) cited by Free (l970) observed that after bee visits, the inner nectaries of rape were empty. Five minutes later the nectar- ies had secreted a small amount of nectar and 30 minutes later they were full again. Materials and Methods | Nectar replacement in pistillate cucumber flowers with removal at hourly_intervals.--Caged pistillate flowers of the cultivar MSU 356 90 were sampled from July 29 through August 29, I969. Each morning at 9:30 four pistillate flowers were marked and the nectar removed care- fully so not to injure the nectary tissue. At hourly intervals from 9:30 a.m. to 2:30 p.m., nectar was removed from the same four flowers. Each hour, starting at 10:30 a.m. and ending at 2:30 p.m. two differ- ent flowers were picked as controls and their nectar removed. Results When nectar was removed from pistillate flowers at hourly inter- vals over a six hour period, the flowers replaced approximately the same volume of nectar that was removed the hour before (Table 29). Nectar replacement was slightly higher in the morning than in the after- noon. The overall mean value for the morning was l.3h ul and l.lO ul for the afternoon. The volume of nectar of the controls on the other hand increased throughout the day going from an average of l.40 ul at 9:30 a.m. to a high of lO.38 ul at l:3O p.m. Table l5 dealing with the secretion cycle of the pistillate flower shows similar results. The sum of the average values for the experimental group over the six hour period of removal was 7.33 microliters. This is less than three of the hourly average values for the control group. Therefore, it would appear that multiple visitation in the cucumber does not stimulate nectar secre- tion. To look at this in a different way, the production of nectar for each flower, being sampled six times, was totalled. The total produc- tion for each flower over the six hour sampling period was from 0.49 to 2l.7l ul with a mean of 7.l8 t .55 ul/flower. Once again this value is less than three hourly average production values for the control group. 9] Therefore, nectar removal did not stimulate nectar production in pistil- late cucumber flowers. Even though the flower was able to almost replace the volume of nectar that was removed the hour before, the sugar concentration and actual weight of sugar in the nectar decreased sharply over the six hour removal period. The sugar concentration of the experimental group dropped from h2.3% at 9:30 a.m. to l3.8% by 2:30 p.m. (Table 30). The hourly sugar concentrations of the control group did not change signifi- _cantly, falling within a range of 39.3% - h2.8% sugar. The significant decrease In sugar concentration following nectar removal is substantiated by the literature review. The weight of sugar in the nectar decreased from .76 mg of sugar at 9:30 a.m. to .lS mg at 2:30 p.m. for the experimental group (Table 3]). While the flowers that had hourly nectar removal showed a steady de- crease in sugar weight, the controls had an increase, going from .76 mg at 9:30 to a high of 4.98 mg at l:30. The sum of the average values over the six hour period during removal, showed the mean weight of sugar being replaced hourly was 2.36 mg, which is less than four average values for the control group (Table 3l). Thirty eight of the flowers having nectar removed hourly had sugar production values for all six of the sampling times and produced from .2l to 5.03 mg of sugar with a mean of 2.l9 mg. This value is less than five of the average readings for the control group. Therefore, it would again appear that nectar removal does not stimulate sugar production in cucumber nectar. The reason that there are only 38 flowers with six sugar produc- tion values, is that a sample of .A9 ul of nectar, seldom makes a large enough drop on the prism of the refractometer to be read. 92 Table 29. - The average volume of nectar replaced in pistillate cucumber flowers after removal at hourly intervals. Time Removal Avg. vol. nectar % of flowers Control Avg. vol. Sample size (ul) producing Sample size nectar nectar (ul) 9:30 89 l.h0 t O.ll 83% 89 l.h0 t O.ll lO:30 88 l.2l f 0.08 89% 2h h.h2 t 0.h8 ll:30 88 l.hl f O.I2 93% 2h 5.75 t 0.76 l2:30 78 l.l2 f 0.l0 82% 22 9.22 f 0.96 1:30 69 1.10 f 0.15 77% 20 10.38 t 1.20 2:30 65 I.05 t 0.22 SI% 20 9.58 t 0.85 Table 30. - The average sugar concentration of nectar replaced in pistillate cucumber flowers after removal at hourly intervals. Time a. fgflgagfl_ Avg. % sugar Control Avg. % sugar Sample size Sample size 9:30 67 h2.3 t 0.53 67 h2.3 t 0.53 10:30 73 311.3 t 0.81 ' 21 112.8 :I; 1.20 ll:30 7h 26.h f 0.82 2h h2.2 t l.l5 l2:30 58 2l.9 t 0.87 20 91.4 i l.68 1:30 43 17.8 t 0.79 20 ' 39.3 t 1.80 2:30 28 l3.8 f 0.76 20 h2.h t 2.h8 Overall 26.l f h.35 hi.7 t .52 93 Discussion Possibly the pistillate cucumber flower does not respond to multiple visits by secreting more nectar and sugar since it has basi- cally only a one day secretion cycle. Most of the plants used by other researchers in this area had secreting cycles of more than one day. Since recent work suggests that nectar secretion results from metabolic activity of the nectary, we might anticipate that nectar removal may set up a physiological response that would affect the metabolic rate of secretion for flowers secreting for more than one day. If a bee visit results in pollination, then an opposing response may be stimulated. Shuel (l96l) found that the stigmatic surfaces of flowers Streptosolen [amesonii from which multiple collections of nectar had been made, re- mained comparatively dry. A later study showed that periodic removal 0f nectar caused a 50% reduction in the yield of stigmatic exudate. There- fore, he suggested that under normal circumstances part of the stigmatic exudate is derived from nectar which has been reabsorbed into the flower. Pollination may have a drying effect on the stigma, which might decrease the need for nectar and sugar-production by the nectary tissue for this reabsorbing process. Materials and Methods II Nectar replacement every fifteen minutes.--Since the previous study showed that a flower could replace approximately the same volume of nectar that was removed one hour before, a small pilot study was set up to determine how rapidly nectar replacement takes place after removal. On August 2], I969, four pistillate flowers of the cultivar MSU 350 were 99 selected within the cage used in the previous study. Instead of remov- ing the nectar once every hour, it was removed every l5 minutes. Results Twenty six per cent of the original volume of nectar was re- placed in the first l5 minutes, 15% was returned during the second l5 minutes and l3% during the third l5 minutes. As in the previous study, the sugar concentration and total weight of sugar present decreased with removal (Table 32). Materials and Methods III Nectar replacement every 5 minutes.--Starting on September I, I969, caged pistillate flowers of the cultivar MSU 350 were sampled in the afternoon for five days. The nectar was removed from each flower every five minutes. Results Nectar replacement in a cucumber flower is a rapid event. Forty per cent of the original volume of nectar was replaced in the first five minutes after removal (Table 33). Thirty two per cent was replaced in the second five minutes and 29% after the third removal. .Since the study only covered 20 minutes, decreases in sugar concentration and total weight of sugar were not as large as with removal every hour. Discussion Even though nectar secretion appears to be related to metabolism in the nectary tissue, there may also be an osmotic relationship between 95 Table 3|. - The average weight of sugar in nectar replaced by pistillate cucumber flowers after removal at hourly intervals. Time Removal Avg. wt. sugar Control Avg. wt. sugar Sample size (mg) (mg) 9:30 80 0.76 t 0.06 80 0.76 1- 0.06 10:30 82 0.51 t 0.0h 21 2.20 t 0.21 11:30 80 0.95 f 0.05 29 2.76 t 0.30 12:30 72 0.27 t 0.02 20 h.62 t 0.36 1:30 59 0.22 t 0.03 20 4.98 t 0.61 2:30 59 0.15 t 0.03 20 h.80 t 0.56 Table 32. - The average volume of nectar, sugar concentration, and total weight of sugar in the nectar replaced after removal at 15 minute intervals. Time N Avg. vol. N Avg. sugar N Avg. weight of (ul) concentration sugar (mg) (‘70) 2:45 A 2.81 t 1.28 h 30.3 f 1.98 h 0.95 t 0.h0 3:00 A 0.73 t 0.28 2 27.2 t 2.80 2 0.37 t 0.0h 3:15 A 0.93 t 0.21 2 23.8 t 0.05 2 0.19 t 0.06 3:30 A 0.36 i 0.21 1 18.5 t l 0.19 t N = Sample size Table 33. - The average volume of nectar, sugar concentration, and total weight of sugar in the nectar replaced after removal at 5 minute intervals. Visit N Avg. vol. N Avg. sugar N. Avg. weight of number (ul) concentration sugar (mg) (%) 1 5h 3.0h t 0.2% 53 35.9 t 0.86 #6 1.21 t 0.08 2 SH 1.23 t 0.12 “3 33.4 t 0.87 37 0.98 t 0.0“ 3 54 0.98 t 0.11 36 31.7 t 1.hh 33 0.33 t 0.03 h 36 0.87 t 0.11 28 32.0 t 1.23 23 0.33 f 0.0h 96_ the secreted nectar and nectary tissue as was suggested by Raw (1953). Without rapid replacement of nectar, cucumber flowers would become un- attractive to bees and since there are few flowers per acre bees would soon leave cucumbers for other, more attractive sources. Rapid replace- ment of nectar allows bees to revisit the same flowers thus keeping cu- cumber flowers competitive in attracting pollinating bees. I The Concentration of Cucumber Nectar at the Time of Collection by the Bee Throughout the Day Kauffeld and Williams (1972) found the honey stomach contents of bees working cucumber ranged from 36% - 41% sugar, depending on weather conditions. Wilson, Moffett and Harrington (1958) in analyzing the honey stomach contents of 18 bees, found that cucumber nectar aver- aged 42.2% sugar with a minimum of 37.8% and maximum of 49.2% in Colorado. Pedersen (l953b) found that when bees were caged with plants, the sugar concentration of the nectar appeared to be lower than under natural con- ditions. The method of removing and analyzing honey stomach contents has been questioned and studied by several researchers. The method was used by Nye and Pedersen (1962), Pedersen (l953b), Scuilen (1940,1942) and Butler (1945). Shaw, Farr and Goldstein (1953) tested the method and found that after killing the bees with cyanide, there was no significant difference in the sugar concentration of the nectar within 15 minutes after the bee had died. They did, however, find that a reduction in sugar concentration occurred if the nectar was analyzed 30 minutes after the bee was dead. Montgomery (1958) on the other hand reported that no change occurred in the sugar concentration of the nectar up to 42 hours. 97 Park (1932) is generally given credit for disproving the theory that honey bees extract and get rid of water from the nectar while carry- ing it back to the hive. He found that the concentration was altered only very slightly, in the form of a decrease of about one per cent. This decrease appeared to be greater for nectar of high concentration than low. Simpson (1964) and Free 8 Durrant (1966) found that the dilu- tion was due to the bees mixing saliva with it from the labial glands. The dilution was greater for the more concentrated nectar. Bailey, Fie- ger and Oertel (1954) stated that the honey stomach contents were a mixture of honey and nectar and that rapid hydrolysis of sucrose took place in the honey stomach of the bee which could account for a slight reduction in water content. Vansell (1934,1942) found that the average concentration of nectar in the honey stomachs of collecting bees corresponded closely to the concentration in the flowers. Woodrow (1968) recorded ranges as great as 25% in the sugar concentration of nectar in individual bees foraging on a single natural source. Bees having small amounts of nectar in their nectar sacs were discarded by Shaw, Farr and Goldstein (1953) and Wilson, Moffett and Harrington (1958), since data from such samples were found to vary and usually indicated extremely low sugar concentrations. Oertel (1946) on the other hand combined 2 or more bee samples when one sample was too small. Materials and Methods Honey bees were collected from cucumber flowers during the first two weeks of August, 1970. When a bee was observed working a 98 cucumber flower, it was caught and killed in a cyanide killing jar. Within five minutes after collection, the head of the bee was removed and honey stomach contents squeezed onto the prism of the refracto- meter for analysis. A total of 495 bees were collected and the data sorted by the hour to see how the sugar concentration varied throughout the day. Results The sugar concentration of the honey stomach contents did not vary a great deal during the day.- The average values ranged from 17.1% to 28.3% sugar (Table 34). Overall the average was 24.5%. The morning values were highest averaging 26.0% and the afternoons 23.0%. Values peaked at 9-10 a.m. and 12-1 p.m. with a decrease throughout the rest of the afternoon. The lowest. averages were at 8-9 a.m. and 3-4 p.m. which would generally be expected. The range of values shows that the lowest concentration carried by a bee was 2.6% and the highest 46.5%. Discussion Tables 15 and 16 show that nectar taken directly from pistillate flowers averaged 36.3% and from staminate flowers 45.3% sugar during the day, when bees were excluded from the blossoms. The overall mean of the two values is 40.8% while the overall average sugar concentration of nectar from bee's honey stomachs was 24.5%, a 40% decline (Table 34). In an earlier study on the concentration of nectar removed from flowers at hourly intervals (Table 30), the sugar concentration dropped from 42.3% to 13.8% with a mean of 26.1%. Since the average concentration of the contents of the bee's honey stomachs was so close to the mean 99 value obtained from the nectar replacement study, it can be assumed that if bees are properly chosen, honey stomach content of bees working cucum- ber provides a legitimate and simple means of obtaining nectar for analysis. The method might well be suitable for monitoring nectar secre- tion In a plant breeding program. These studies have brought out the important point that nectar replaced after removal is of lower sugar concentration than nectar which has not been removed from the nectary. Errors in interpreting nectar analysis could result from ignoring this phenomenon. Cucumber flowers would typically be visited several times an hour by honey bees. Each bee load is an accumulation of small quanti- ties of nectar from many individual flowers and the range of values shown in Table 34 would lead one to suspect a wide variation in sugar concentration is acceptable to foragers repeatedly visiting the same field. Wbodrow (1968) made similar observations. Connor (1969) found maximum bee flights in the field to extend from 9 a.m. to 2 p.m. During this period, the sugar concentration values averaged 26.6% compared to 21.0% for early morning and late afternoon. This study indicates a correlation between nectar concentration and the presence of bees on the crop. Brett and Sullivan (1972) said that the most attractive flowers have sugar concentrations above 20% and the sugar concentrations of nectars have been found to range between 5% - 74% Percival (1965). On this basis, cucumber nectar would be rated moderately attractive to honey bees. Collison and Martin (1970) noted tl1at bees located near cucumber fields visited many other plants in the area for necta r . 100 Since some authors discarded small samples with low sugar con- centrations, the data used in Table 34 was reanalyzed, excluding any values less than 10% (Table 35). No new trends were found. The Effect of Pollination on Nectar Secretion Davidson (1922) claimed that osmotic pressure within the plant forces open the flowers, keeps them open and supplied with nectar until pollination takes place. Pollination results in reducing the pressure, the nectar flow ceases, the floral parts fade and wither or fall off. Swanson and Shuel (1950), Oertel (1956), Melnichenko (1963) and Barbier (1962) all reported that secretion by floral nectaries decreased soon after pollination and ceased with fertilization. Veprikov (1936) quot- ing Gorski as cited by Beutler (1953) found that nectar secretion in cucumbers ceased after pollination, and the corolla fell at the same time. Kaziev and Seidova (1965) found that pistillate flowers of Cucurbitaceae secrete nectar intensely before pollination and after this process nectar secretion ceased. If pistillate flowers of cucumbers, melons and watermelons were isolated from pollination, they could secrete nectar continuously for 2-3 days. Materials and Methods Three studies, with different approaches, were run to find the effects of pollination on nectar secretion. 19§§A,--Pistillate flowers of the cultivar Piccadilly Med. 11 were used in the greenhouse during this study. Each day at 7 a.m. the plants were checked for newly opened flowers on vines where no fruit 101 Table 34. - Concentration of cucumber nectar in the honey stomachs of honey bees throughout the day. Time Sample Avg. sugar Range of values size concentration 8:00 - 9:00 58 22.7 f 1.43 6.3 - 38.6 9:00 -10:00 94 28.3 t 0.98 6.9 - 46.5 10:00 -11:00 70 27.0 f 1.19 6.5 - 38.7 11:00 -12:00 76 26.2 t 1.30 6.8 - 40.0 12:00 - 1:00 97 27.5 t 0.97 7.7 - 39.9 1:00 - 2:00 41 23.9 f 1.77 7.1 - 38.3 2:00 - 3:00 27 23.3 i 1.41 10.0 - 32.0 3:00 - 4:00 32 17.1 t 1.55 2.6 - 33.7 Overall 24.5 f 1.28 Table 35. - Concentration of cucumber nectar in the honey stomachs of honey bees after removal of low values. Time Sample size Avg. sugar conc. 8:00 - 9:00 45 26.9 1 1.28 9:00 -10:00 84 30.7 t 0.74 10:00 -11:00 64 28.8 t 1.06 11:00 -12:00 66 28.8 t 1.18 12500 - 1:00 88 29.4 t 0.83 1:00 - 2:00 34 27.0 i 1.67 2:00 - 3:00 27 23.3 t 1.41 3:00 - 4:00 22 21.2 t 1.60 102 had been previously set or growing. Due to lack of plants without fruit, an equal number of flowers to serve as controls were used on vines where only one fruit was developing. At 7:30 a.m. the nectar was removed from the flowers. Following the removal of nectar, the first group of pistil- late flowers were hand pollinated with a camel hair brush. The controls were not pollinated after nectar removal. The nectar of all flowers was again removed at 11:30 a.m. and at 3:30 p.m. from both groups. The flowers were tagged and clipped shut after the last nectar removal to see if fruit developed. 12§§§:--Field studies commenced on August 14 and ended on Septem- ber 10. Groups of four pistillate flowers of the cultivars Piccadilly and MSU 350 were bagged the evening before anthesis. Each morning at 8:30 two of four flowers in a group were hand pollinated with a camel hair brush and re-covered with cloth bags. At 2:30 one of the pollin- ated flowers and one of the controls were picked by removing the flowers at the perianth with attached style and stigma. The nectar was removed, volume determined and refractometer readings taken. The other pollin- ated flower and control were picked at 8:30 a.m. the next day and the nectar removed. After the flowers were removed at the perianth, the remaining ovary was left on the vine to check for fruit development. 1969.--This field study used pistillate flowers of the cultivar MSU 350. Bagged flowers were pollinated on the day of anthesis at 4:30 p.m. with staminate flowers from the cultivar SMR 58. The flowers were picked the following morning at 8:30 a.m. by removing them at the perianth. The nectar was removed, measured and refractometer readings 103 taken. Seed counts were taken on the fruit that developed from the ovaries that were left on the vine. Results 1968A3--Since the first nectar was removed at 7:30 a.m. not all of the flowers had started to secrete (Table 36). When the nectar was removed from the same flowers at 11:30 a.m., 5% fewer of the pollinated group and 3% more of the control group contained nectar. Therefore, it would appear that pollination had affected nectar replacement. Going back to the data on the study dealing with nectar removal once every hour; at 9:30, (time of first removal), 83% of the flowers were produc- ing nectar, at 10:30 (second removal), 89% and at 11:30 (third removal), 93% were producing nectar (Table 29). Since the percentage of flowers producing nectar increased even though the nectar was being removed hourly and now with removal and pollination, the per cent decreased, it would appear that the observed decrease was not due to nectar replace- ment but rather to pollination. By 3:30 p.m. both the pollinated and control groups were similar again in the percentage of flowers producing nectar. This was probably due to the previous removals and natural de- crease in secretion rate in late afternoon (Table 34). Possibly the pollinated group reached a secretion decline earlier in the day. To know for sure, the sampling times would have to be changed. The average ‘volume ofnectar secreted at 11:30 by the two groups partially supports 'the hypothesis of earlier secretion decline due to pollination (Table 137). The pollinated group secreted 4.88 ul compared to 5.16 u1 for the (nontrols. But at 7:30_a.m. the controls had secreted less than the 104 pollinated group.' Looking at the differences of the two periods for each group shows that controls produced 3.50 ul for the four hour period compared to 2.40 for those pollinated. These values further support the proposed hypothesis. Also, when you look at the produc- tion of nectar at 3:30 the pollinated group again has less, 0.32 ul compared to 0.66 for the controls. - When looking at the total secretion pattern for the day, the differences no longer show up, (Table 37). The pollinated group pro- duced 7.68 u1 for the day and controls 7.48. A possible explanation for this, is that the control flowers came from vines where a fruit was developing. Therefore, large amounts of the plants carbohydrate supply was being used for fruit and seed development. This suggests a need for further research dealing with the effects of fruit develop- ment on nectar secretion. The total weight of sugar produced by the two groups was in agreement. The controls produced 3.13 mg and the pollinated group 3.80 mg. When the zero values were averaged in (Table 38), the pollinated group produced 2.94 mg and the controls 2.61 mg. Both groups showed similar decreases in sugar concentration as the nectar was removed throughout the day. The pollinated group decreased from 41.9% - 19.3% and control group from 45.3% - 18.1%. A similar decline was shown in Table 30 where the nectar was removed at hourly intervals. A significant difference was observed in the total weight of sugar that was produced at 11:30 a.m. The pollinated group produced 1.5 times more sugar than the control group. Once again this may be attributed to the presence of fruit on the control vines. 105 The study shows that nectar replacement will continue even though the flower has been pollinated. The average volume of nectar produced by the pollinated group at 11:30 was almost twice the volume produced at 7:30. The average sugar weights reported in Table 37 are based only on those flowers that were producing enough nectar to measure on the refractometer. including the unmeasurable samples in the analysis as having 0.00 mg of sugar did not significantly change the results (Table 38). Both the average values and the differences between them were smaller. In Chapter 11 some work dealing with the flower's position on the vine was reported. The positions on the vine of the hand pollin- ated flowers in this study were recorded and the results are shown in Table 39. As was found in previous studies, flowers found on lateral vines tended to produce a larger quantity of nectar, containing a higher weight of sugar than those on the main vine. But with nectar removal and pollination the flowers on the lateral vines were more definitely affected than those on the main vines. From 7:30-ll:30 the main vine flowers increased their nectar production 2.98 times compared to 1.02 times for lateral vines. Similar results are seen in total weight of sugar present. Total production over the entire day Showed the main vine flowers to be slightly more productive in volume and sugar weight than lateral ones. For each time period, the sugar concentrations between the two positions were not significantly different. In the above study all hand pollinated flowers developed fruit except two. 106 12§§§:--Even though every mean value for nectar secretion was lower in the hand pollinated group than the equivalent one in the con- trol group, the t-test shows that all but two of the comparisons were not significantly different (Table 40). The lack of significant differ- ences may be due to the fact, that in this study, only pollination is involved, not nectar removal too. Nectar was removed only once, at 6 or 24 hour intervals after pollination and the 0.00 values for the total amount of sugar as well as volume were included in the data analysis. Nectar volume values for both the pollinated group and the con- trols were significantly lower for the 24 hour sampling than the 6 hour. This would be expected since there was an overnight involved to complete the 24 hour period after pollination. Sugar concentration and total weight of sugar was drastically reduced for both groups also. This was probably due to the reabsorption of sugar during the night. In this study after 24 hours the pollinated group had significantly less nectar and sugar than the unpollinated controls. Therefore, it would appear that nectar secretion was affected sometime between 6 and 24 hours after pollination. None of the flowers that were removed at the perianth at the end of 6 hours after being pollinated developed fruit, whereas 40% of those removed after 24 hours developed normal fruit. There was a large difference in the two cultivars used in the experiment, only this time it was not due to the sex of the flower and the cultivars flowering pattern, since only pistillate flowers were sampled. Within the six hour period after pollination, MSU 350 produced 1.67 times more nectar and in the 24 hour period 2.13 times more than 107 Table 36. - The percentage of the flowers producing nectar throughout the day after the nectar is removed and pollinated (1968 A). the flower Time Pollinated group, Control group 7:30 85% 92% 11:30 80% 97% 3:30 32% 30% Sample sizes for both groups was 40. Table 37. - The volume of nectar, sugar concentration and total weight of sugar produced after the nectar was removed and flowers pollinated in the greenhouse. Time N Avg. vol. N Avg. sugar N Avg. wt. of (ul) conc. %9 sugar (mg) Pollinated group 7:30 40 2.48 f 0.52 33 41.9 i 1.38 33 1.25 t 0.17 11:30 40 4.88 t 0.72 28 28.5 i 1.26 28 2.33 f 0.29 3:30 40 0.32 i 0.11 10 19.3 t 1.60 10 0.22 t 0.05 Total 40 7.68 3.80 Control group 7:30 40 1.66 f 0.26 28 45.3 f 1.16 28 1.12 t 0.15 11:30 40 5.16 t 0.62 38 25.5 i 0.97 38 1.53 t 0.19 3:30 40 0.66 t 0.26 8 18.1 t 2.31 8 0.48 t 0.12 Total 40 7.48 3.13 N = Sample size. Table 38. - The average weight of sugar produced after the nectar was removed and flowers pollinated with zero values included. Time Sample size Pollinated Sample size Control Avg. wt. sugar Avg. wt. sugar 7:30 39 1.06 t 0.16 31 1.01 t 0.15 11:30 36 1.82 t 0.28 39 1. f 0.19 3:30 37 0.06 f 0.02 36 0.11 f 0.04 Total 2.94 2.61 108 Piccadilly (Table 41). The controls likewise showed MSU 350 producing 1.94 times more nectar at 6 hours and 1.33 times more after 24 hours. lr1three out of fourwcomparisons Piccadilly had a slightly higher sugar concentration. In totaL MSU 350 produced more sugar three of the four times. At six hours it contained 1.60 times more sugar when pollinated and 1.43 times more when not pollinated. After 24 hours it contained 2.12 times more sugar when pollinated. Every mean value for the pollinated group was lower than the equivalent for the controls, except one (Table 41). The Student's t test, however, showed only one comparison to be significant at the .05 probability level. The cultivar Piccadilly, 24 hours after pollina- tion contained significantly less nectar than the controls. The culti- var MSU 350 was found to contain significantly less nectar and weight of sugar than the controls at the .10 probability level. Table 40 ' shows that there were significant differences in both volume of nectar and total weight of sugar present after 24 hours when the data of both cultivars was combined. Separation by cultivars, made the sample sizes too small for differences to be detectable. From the group of flowers that were pollinated and flowers re- moved 24 hours later, comparisons were made between those that developed fruit and those that did not, to see if there was a difference in nectar secretion (Table 42). Even though the values in the group that developed fruit were lower than the group that did not, the t test showed that they were not significantly different at the .05 probability level. The percentage of flowers containing nectar at the time of sampling, would tend to indicate that sometime between 6 and 24 hours 109 Table 39. - The influence of flower position on nectar secretion in flowers where the nectar supply is removed and the flower pollinated. Time N Avg. vol. N Avg. sugar N Avg. wt. of (ul) concentration sugar (mg) Main vine 7:30 26 1.84 t 0.30 23 03.3 t 1.20 25 0.90 t 0.10 11:30 26 5.48 f 0.91 19 28.5 + 1.73 23 2.10 t 0.36 3:30 26 0.41 f 0.15 8 19.7 f 1.65 23 0.08 t 0.03 Total 7.73 3.12 Lateral vine 7:30 10 3.68 f 1.36 10 38.8 H" 3.51 10 1.26 t 0.38 11:30 14 3.76 + 1.15 9 28.6 + 1.57 13 1.31 + 0.00 mm m 0M+001 2 n5 H- 5.90 14 0.02 |+ 0.02 Total 7.58 2-59 N = Sample size Table 40. - The effect of pollination on nectar secretion (1968 B). N Pollinated -'6 hours N Control -‘6 hours Avg. volume 25 9.73 t 1.39 ul 25 11.68 t 1.60 ul Avg. sugar 25 30.4 t 1.30 % 24 30.8 t 1.55 % concentration AVg. amt. 25 3.14 f 0.42 mg 25 3.79 i 0.50 mg of sugar N Pollinated -_24 hours N Control -.24 hours Avg. volume 25 2.30 f 0.77 u1* 25 6.58 i 1.50 u1* Avg. sugar 10 12.2 f 1.12 % 18 15.1 t 2.31 % concentration Avg. amt. 23 0.31 t 0.11 mg* 24 0.91 f 0.21 mg* of sugar N Sample size sh I s Comparisons significantly different at the 0.05 probability level. (Students t test) 110 Table 41. - The effect of pollination on nectar secretion for the cultivars MSU 350 and Piccadilly. N Pollinated 6 hrs. N Piccadilly (Avg. vol.) 7 6.55 t 1.24 ul 7 MSU 350 (Avg. vol.) 18 10.96 t 1.80 ul 18 Piccadilly (Sugar conc. 7 32.2 f 3.11 % 6 MSU 350 (Sugar conc.) 18 29.3 t 1.80 % l8 Piccadilly (Sugar wt.) 7 2.19 t 0.00 mg 7 MSU 350 (Sugar wt.) 18 3.51 t 0.50 mg 18 N Pollinated 24 hrs. N Piccadilly (Avg. vol.) 7 1.27*t 0.57 ul 7 MSU 350 (Avg. vol.) 18 2.70 f 1.04 ul 18 Piccadilly (Sugar conc.) 4 11.6 t 2.34 % 5 MSU 350 (Sugar conc.) 6 12.5 t 1.23 % 13 Piccadilly (Sugar wt.) 6 0.17 t 0.09 mg 6 MSU 350g(§ugar wt.) 17 0.36 t 0.10 mg 18 N Sample size J. I \ Comparisons significantly different at the 0.05 (Students t test) Control 6 hrs. 6.97 2.80 ul 1+ 13.51 i 1.79 ul 35.4 H" 2.39 % 29.3 t 1.80 % 2.89 1,-1.18 mg 0.10 t 0.53 mg Control 24 hrs. 5.30*t 1.70 ul 7.07 1+ 1.99 ul 19-7 t 6.77 % 13.4 3+ 1.92 % 1.02 H- 0.46 mg 0.87 f 0.25 mg probability level. Table 42. - Nectar secretion in cucumber flowers 24 hours after pollination comparing successful pollination (fruit ful pollination (no fruit formed). formed) with unsuccess- N Developed fruit N Avg. volume 10 1.62 f 0.94 ul 15 Avg. sugar conc. 4 11.8 t 1.45 % 6 gflyg. sugar weight 9 0.23 t 0.13 mg 14 No statistical differences at 0.05 probability level. N2 fruit development 2.75 t 1.13 ul 12.4 t 1.71 % 0.37 t 0.16 mg (Students t test). 111 after pollination nectar secretion was affected by pollination (Table 43). Twenty four hours after pollination, only 48% of the pollinated flowers contained nectar compared to 76% for the controls. l969.--Since it seemed that the effects of pollination showed up some time between 6 and 24 hours after pollination, this study sampled the flowers 16 hours after pollination. With this timing it was impossible to avoid an overnight, therefore, the reabsorption of sugar is incorporated into the data for both groups. Because the cucumber flower has basically a one day secretion cycle, pollination at 4:30 in the afternoon may be too late to detect any effects due to pollination (Table 44). No significant differences were found in nectar volume, sugar concentration, or amount of sugar between the pollinated and control groups. 0f the 99 flowers that were pollinated, 29 developed fruit. They contained 10-461 seeds and averaged 188 seeds per fruit. Since only 29% of the pollinated flowers that were removed at the perianth developed into fruit, the pollinated group was sorted on the basis of fruit development (Table 45). The Student's t test shows that only the comparison of sugar concentration between the two groups was signifi- cant at the .05 probability level. Differences in volume of nectar and total weight of sugar were not significant. Sixty four per cent of the pollinated flowers contained nectar and 67% of the controls which shows no significant difference. 112 Table 43. - The effect of pollination on the percentage of flowers producing nectar. .Qiggp - Sample size ‘% Producing nectar Pollinated - 6 hours 25 100% Control - 6 hours 25 96% Pollinated -24 hours 25 48% Control -24 hours 25 76% Table 44. - The effect of pollination on nectar secretion 16 hours later (1969). fl| Pollinated ‘N Control Avg. volume 99 2.74 f 0.44 ul 81 2.44 t 0.36 ul Avg. sugar conc. 50 17.8 t 0.80 % 47 17.8 t 0.83 % Avg. wt. of sugar 86 0.63 t 0.11 mg 74 0.51 i 0.09 mg N = Sample size No statistical differences at 0.05 probability level. (Student t test) Table 45. - Comparison of the pollinated flowers with regard to fruit development when the flower was removed and nectar sampled 16 hours after pollination. fl Developed fruit fl_ 'Ng fruit development Avg. volume 28 1.98 t 0.59 ul 71 3.04 t 0.56 ul Avg. sugar conc. 15 10.3 t 0.92 %? 35 19.0 t 0.97 %0 Avg. sugar weight 25 0.34 t 0.11 mg 61 0.75 t 0.14 mg N = Sample size Comparisons significantly different at the 0.05 probability level- (Student t test) 113 Discussion The results of the three studies indicated that only morning I pollination affected nectar secretion. Pollinations late in the after- noon failed to affect nectar secretion. The 19688 study indicated that possibly no new nectar was produced after fertilization. These studies also showed, using stigma and style removal at the perianth as an indi- cator that some fertilization takes place between 6 and 16 hours after pollination. Connor (1969) found with a similar procedure that no fruit developed three hours after pollination but 2 of 5 fruit developed 12 hours after pollination, averaging 64 seeds per fruit. In another study which will not be reported at this time, a minimum of 7 1/2 hours was needed before any fruit developed that contained seeds. The literature search and these studies suggest that nectar secretion ceases after fertilization, which requires at least 7 1/2 hrs. after pollination. From the time of bee pollination to fertilization, the cucumber flower continues to secrete nectar and replenish its supply after each visit. l\ny nectar remaining at the time of fertilization may change in sugar concentration due to changes in the relative humidity and may be partially reabsorbed during the night. Another study in which pollinations were ckone in the early morning and nectar samples taken at night would be desirable to verify this hypothesis. 1 It is advantageous for the crop not to cease nectar secretion at the time of pollination. Otherwise, the crop would be unattractive no bees in the afternoon. Instead of bee activity peaking at 11 a.m., it would be on a rapid decline. If nectar secretion were to cease with 114 the first visit resulting in pollination, chances are the level of pollination needed in the field would not be accomplished and fruit set would decrease. Comparison of the Attractiveness of Staminate and Pistillate Cucumber Flowers to the Honey Bee Sanduleac (1959) found that staminate flowers were visited more frequently than pistillate, indicating that many bees were collecting pollen in cultivars of Cucurbita maxima, £3 pepo and £3 moschata. Mann (1953) found that bees collecting nectar from flowers of Cucumis mglg_ spend about 8-9 sec/flower/visit. Staminate flowers have shorter corolla tubes and honey bees can more easily reach the nectaries. Hermaphroditic flowers have deeper corolla tubes and the entrances are more constricted, so that honey bees have to squeeze between the anthers and stigmas to reach the nectary and in so doing transfer pollen to the stigmas. Although bees passed readily from one type of flower to the other, there was a slight preference for hermaphroditic flowers when equal numbers of each were present. Such a preference probably also existed in the field after mid-day as pollen collection was found to reach a peak at about 11 a.m. and then rapidly diminish, whereas nectar collection declined rnuch less abruptly. Bees remained at perfect flowers longer than at sstaminate ones. The average time spent on perfect flowers (1 visit per t>ee) was 8.54 sec. and on staminate flowers (2 visits per bee) was 5.66 sec. Bees spent about one and one-half times as long visiting perfect 'flowers as they did staminate flowers. 115 Materials and Methods Relative attractiveness of staminate and pistillate flowers is partly indicated by the average time spent on each type of flower. To obtain data on this in l968 honey bees working the cultivar Piccadilly were followed and timed with a stopwatch. Since this cultivar produced more staminate than pistillate flowers each day, more data was taken from staminate than pistillate flowers. The honey bees were timed at differ- ent periods during the day from July 22 to August 23, 1968. The time started when they began working the center of the flower for nectar and ended when they finished removing nectar from the flower. Often a honey bee will stop and groom itself after removing nectar from a flower be- fore moving on to the next one. The time spent in grooming was not in- cluded in our timings. Results Throughout the entire day honey bees spent more time per visit [on pistillate flowers than on staminate flowers (Table 46). Honey bees averaged from 7.8 - 16.0 sec. on pistillate flowers with an overall mean of 12.6 sec. compared to a range of 5.0 - 7.3 sec. and a mean of 6.3 for staminate flowers. For the entire day honey bees spent twice as long on pistillate as on staminate flowers. The average maximum time spent on pistillate flowers was between 7-8 a.m. and on staminate flowers from 8-9 a.m. Comparison of the morning and afternoon values shows that honey bees spent 1.86-2.25 times longer on pistillate than on staminate flowers in the morning compared to 1.42-2.73 times longer in the afternoon. 116 Discussion In Chapter I it was found that the nectaries of pistillate flowers were 1.6-1.9 times wider and had secreting surfaces approxi- mately twice as large as nectaries of staminate flowers. Also in Chap- ter 11 it was found that pistillate flowers produced from 1.5-2.3 times more nectar than staminate flowers. These values help to explain why the honey bee spent twice as long on pistillate as on staminate flowers. This study indicates that the length of the visit is dependent on the amount of nectar present. As was shown earlier, honey bees if not disturbed, will remove all of the nectar present in one visit. Pedersen (1953b) showed that honey bee visitation was correlated with the amount of nectar available per plant. Connor (1969) found the activity of honey bees on cucumber flowers peaked at 11 a.m. and maximum bee flights in the field extended from 9 a.m. to 2 p.m. In this study, prior to 9 a.m. the average time spent on each flower was greater than values for the rest of the day (Table 46). Until 9 a.m. fewer bees were observed in the field working the flowers. Due to the lower level of competition for flowers and the fact that flowers were being visited for the first time, the flowers contained a larger supply of nectar which required a longer time for re- moval. As bee density increased after 9 a.m., the average time per visit began to decrease because flowers being visited had only partially replenished their nectar supply following removal by earlier bee visits. Connor (1969) found that the length of a bee visit to a pistillate flower 117 decreased as the number of the visits increased. The first visits to a cucumber flower lasted an average of 36.2 sec., while the average length of subsequent visits dropped sharply. Also, as shown earlier, successive removal and replacement of nectar reduces sugar concentra- tion and actual weight of sugar which should make the flower less at- tractive to the bee. Even though this should not affect the speed of nectar removal, it may affect the bee's behavior, so that it is not as efficient in getting all of the nectar present. Data from 2-4 p.m. for staminate flowers and 1-4 p.m. for pistil- late flowers showed late day increases in time spent on the flowers (Table 46). Since sample sizes were small, additional data was taken in 1969 to check on the results (Table 46). Once again there was an increase in values. A possible explanation is that flight activity de- creases after 2 p.m. thus providing more time between bee visits and a resultant increase in nectar replacement and the length of bee visits. 118 : :.o w 0.0 mm : m.N a m.m N: :6 a - m : m.o « _.m mm. s 0.0 u N.@ mm :6 m - N nus_n> mom. m.m o.N_ cuss ._ntuso : 6.0 a m.m mm : m.m 0 a.m. w :6 a - m : 6.0 a o.m mo : m._ w N.m __ :6 m - N : N.o « m.m on. : m.o a m.N o: 26 N - _ _: m.o H N.@ am. : m.o H w.m ma :6 _ - N. : N.o H 0.6 Nam : o._ a m.N_ om z< ._- o. : m.o a o.N _N_ : 8.. w a.m_ N: z< o_- m : m.o m m.N as. : m.N a N.a_ _s z< m - m uun N.o 0 _.N ._. uum m.N 0 0.0. Nm z< m - N cozo_m oomc_Emum oN_m Lozo_w oum___um_a oN_m \oE_u .m>< o_aEmm \oE_u .m>< o.oEmm Ahmmv os_e .moon >oco; >6 mu030.» LonEJoso oumc_Emum 6cm mum—._um_a co “comm oE_N ozu mo c0m_umaeou u .o: o_nmh CHAPTER IV THE CHEMICAL COMPOSITION OF CUCUMBER NECTAR Many researchers have found that nectar is primarily a solu- tion of sugars in varying proportions. The predominant sugars are sucrose and its breakdown products, glucose and fructose. They have been found in most samples of nectar analyzed to date, Wykes (1951b), Caillas (1926), Shuel (1952), Vansell (1929,1944a,1944b,1952) Maurizio (1954,1961), Luttge (1961) and Cotti (1962). Percival (1961), while analyzing the nectar from 889 plant species in 101 families, found ten common types of nectar. She classi- fied these into three broad groups: (1) nectars with dominant sucrose, (2) balanced nectars with about equal amounts of sucrose, fructose and glucose, and (3) nectars with dominant fructose plus glucose. Six sugars, other than the three dominant ones, have been iso- lated in some nectars. These include: (1) xylose, lfteni (1967), (2) melezitose, Beutler (1953), and Percival (1965), (3) trehalose, in sedges only, Beutler (1953) and Percival (1965), (4) melibiose, (5) raffinose, Wykes (1951a,1952b), Beutler (1953), Percival (1961, 1965), and Feltner and Sackett (1964), (6) maltose, Wykes (1951a, 1952b), Bailey, Fieger and Oertel (1954), Beutler (1953), lfteni (1967), lrurgala, Gochnauer and Holdaway (1958) and Percival (1961,1965). 119 120 Percival (1961,1965) found that the sex of the flower in some species of willows affects the nectar composition. The male catkins have a sucrose-dominated nectar, while the female catkins have fructose and glucose predominating. Generally, the age of the flower does not affect nectar composition. Kartashova and Novikova (1964) found a change in nectar composition with age of the flower in only one species out of twelve. Percival (1961,1965) found a change in the nectar of Hibiscus syriaca. Percival (1961) examined the nectar of two species from the family Cucurbitaceae. These were the staminate and pistillate flowers of Luffa cylindrica (Dish-rag or Loofah Gourd) and staminate flowers of Momordica balsamina. All samples had sucrose dominant nectar with fructose and glucose present. Nectar from Luffa cylindrica contained one unknown. Browne (1908) in analyzing honey from flowers of Cucurbi- taceae found that it contained 19.23% water, 72.05% glucose and fructose, 1.89% sucrose, 0.24% ash, 2.55% dextrin and 4.04% of undetermined mate- rials. White §£_§l, (1962) found cantaloupe honey to contain 15.4% water, 37% fructose, 34.51% glucose, 2.89% sucrose, 5.41% maltose and 1.10% higher sugars. Cucumber honey contained 18.7% water, 38.2% fructose, 32.59% glucose, 1.45% sucrose, 5.66% maltose and 0.96% higher sugars. He referred to all reducing disaccharides present as maltose. Test of Gas Liquid Chromatography for Nectar Analysis Many researchers have used variations of paper chromatography for'qualitative and quantitative analysis of nectar; however, this 121 method is time consuming. To expedite this phase of research, gas liquid chromatography was used for qualitative and quantitative nectar analysis. Kleinschmidt, Dobrenz, and McMahon (1968), Butler e£_213 (1972) and Pauratallier (1968) have successfully used gas liquid chromatography in separating sugars that are found in nectar and honey. Materials and Methods Nectar was removed from cucumber flowers and placed in one dram glass screw top vials. The vial covers were lined with aluminum foil since the silylating reagent reacted with the inner covering. Three methods were used to transport the nectar to the laboratory (1) nectar removed, placed in the vial and frozen immediately in dry ice, (2) flowerspicked, placed in a wide mouth thermos bottle with nectar removal taking place upon arrival to the laboratory, Shuel (1968) and (3) bringing the vial with the nectar in it to the laboratory (Table 47). In 1971 all 19 vials of nectar were placed in a freezer until the nectar was frozen. The vials were then placed in a lyophilizer until all visible liquid had evaporated. Next, the samples were placed in the freezer until they were to be analyzed. During September, 1972, an additional 25 samples of nectar were collected and frozen. On Aug- ust 3, 1973, the vials were removed from the freezer and lyophilized. After 4 hrs. they were removed and refrozen until analysis. When the vials were removed from the freezer, 1 m1 of Tri-Sil Z was added. Tri- Sil Z is a commercial silylation reagent produced by the Pierce Chemical Company, Rockford, Illinois. In their “Handbook of Silylation” they reported that Tri-Sil Z is a mixture of N-tri-methylsilylimidazole in 122 dry pyridine (1.5 meq/m) and is used for derivatizing hydroxy and polyhy- droxy compounds in either dry or aqueous solutions. It forms volatile and thermally stable trimethylsilyl derivatives of sugars and related substances, Sweeley g£_gl: (1963). Most silylation procedures have been performed under anhydrous conditions and since nectar is an aqueous solu- tion, Tri-Sil Z was chosen as the reagent. It was also reported that sugars are usually completely silylated when dissolved. It was found that sucrose, fructose and glucose dissolved rapidly and an hour appeared to be sufficient time for the silyation reaction to be completed and stability reached. Standards used for comparison were made from: (1) d(+) Sucrose, Nutritional Biochemicals Corporation, Cleveland, Ohio, (2) Beta-D- Fructose NRC (levulose)-General Biochemicals, Chagrin Falls, Ohio, and (3) dextrose (anhydrous d-Glucose)-Fisher Scientific 00., Fair Lawn, N. J. Ten milligrams of the sugar plus one milliliter of Tri-Sii 2 were used for each standard. The samples were stored in a refrigera- tor. Sugar derivatives were separated by using two different glass columns in 1971. Sucrose was separated using a six foot x 1/8 inch glass column of 5% QF-l on 100/120 mesh Gas Chrom Q at 1800 0, N2 carrier at 120 ml/min and a sensitivity of 1x10-9 amps full scale. Glucose and fructose were separated by using a six foot x 1/4 inch glass column of 10% D.C. 200 on 60/80 mesh 0.0.2. at 1800 C, N2 carrier at 100 ml/min and a sensitivity of 1x10"9 amps full scale. Likewise in 1973 two different glass columns were used to separate the sugar deriva- tives. Sucrose was separated using a six foot x 1/8 inch glass column 123 .0.0 NN.0 00.N. 0.0N N0.0N 2 000 x .00 0..0 NNN0NN0 0N .0.0 .N.0 00.0N 0.0. 00.00. 2 000 00: 00.0 NNNONNO 0N 00. >20 00.0 N0.0N 0.00 00.00 2 >...0muu.2 00.0 NNN0NN0 0N ou. >20 00.0 0N.0m N..0 0N.N.. z 00 2:0 002N NNN0NN0 NN .0.> 00.0 0N.0N :.NN 0..:0 2 00 2:0 002N NNN0NN0 .N 00. >20 .0.0 00.0. N.0N NN.N0 2 00 2:0 0N.N NNN0NN0 0N 00. >20 .0.0 00.N0 0.0N 0N.00. 2 >...0muu.2 002N NNN0N\0 m. ou. >20 .0.0 00.00 ..0N NN.N.. 2 0.00 x 000 00.. NNN0N\0 0. cu. >20 0N.0 ...00 0.0N N..NN. 2 000 002 0.2. NNN0NN0 N. .0.> .0.0 00.0N N.0a .N.N0 z >...0auu.2 00.0 NN\0.\0 0. .0.> 00.0 00.N. 0.00 00.N0 2 >...0muu.2 00.0 NNNO.\0 0. .n.> N0.0 m0.NN N.m: 0N.N0 z 00 0:0 0N.0 NNNO.\m 0. .0.0 00.0 00.0N N.00 00.Na 2 000 00: 00.0 NNN0.\0 0. 00. >20 00.0 00.00 ..00 00.00 2 0.00 x 000 0N.0 NNN0.\0 N. 00. >20 00.0 N0.0N 0..: 00.00 2 >...0muu.2 0.20 NNN0.\0 .. ou. >20 00.0 .0.NN ...0 00.00 2 >...00uu.2 00": NNN0.\0 0. 00. >20 00.0 00.0: N..0 N0.0m z 00 020 00.0 NNN0.\0 0 0u. >20 .0.0 0..N0 0.00 00..0. 2 000 00: 00.0 NN\0.\0 0 .n.> 00.0 00.0. N..0 N0.N0 2 >...amuu.2 00.0 NN\0.\0 N .0.> 00.0 m..0N N.Nm 00.00 2 >...0nuu.2 0..: NN\0.\0 0 .a.> 00.0 N..0N 0.N0 00.00 2 0.00 x 000 00.0 NNN0.\0 0 .n.> 00.0 00.0. N.N0 00.00 2 000 002 0020 NN\0.\0 a .0.> 00.0 m..m 0.N0 00.0. z 00 0:0 0N.0 NNNO.\m 0 .s.> 00.0 00.0N 0.00 N0.00 z 00 2:0 0.20 NNN0.N0 N .0.> 00.0 N0.0 0.00 .0.0N 2 00 020 0020 NN\0.\0 . au. >20 00.0 00.00 0.N0 NN 0N 2 0.00 x 000 00.0 .N\0N\0 0. mu. >20 .0.0 Nm.0 N.NN 00.N. 2 00020022 00.2000 0020 .NN0NN0 0. 0u. >20 00.0 0N.0 ..00 00.N. .z >...0auu.2 0..N .NN0NN0 N. 0u. >20 00.0 0N.0. a.Na 00.0N 2 00020022 00.2000 0.": .NN0NN0 0. .0.> 00.0 .0.N. 0.00 0m..0 2 00020022 00.2000 0.20 .N\_0\0 a. 06. >20 00.0 N..0. a.mN NN.00 2 000 00: 00.0 .NN0NN0 N. .m.> N0.0 No.0. 0.00 0N.00 2 0.00 x 000 00.N .N\.0\0 .. 0052002 00.0 N..0: 0.00 0N.0.. 2 0000 00HN .NNO.\0 0 .a.> 00.0 00.0N ..00 N..00 2 0000 0.2N .NNO.\0 0 00. >20 00.0 0..N0 N..0 .00.00 2 0000 002. .NN0.\0 N 0000. .3 Lomsm wo A.:v .oc co.umuuoamcm2h \2mmam m: .050 .0000 ummam & ..o> 2moooz xom 20>.0_:u 05.0 0000 .m_> .>:ao2mOumEo2co 6.36.. now >0 no~>.mcm 00.0500 20000: 20050000 1 .N: 0.000 124 of 1% D.C. 200 on 60/80 mesh Gas Chrom 2 at 2200 C, N2 carrier at 86 ml/min and a sensitivity of lxlO-8 amps full scale. Glucose and fructose were separated by using a glass column 6 ft. x l/h inch of 3% OV-l7 (5 ft) on G.C.Q. lOO/l20 mesh and l% 0V-l7 (1 ft) on G.C.Q. on 60/80 mesh at l60O C, N carrier at 26 ml/min and a sensitivity of lxlO-9 2 amps full scale. In both cases the type of detector was a hydrogen flame. The peaks were quantitated by peak height ratios. After each injection into the column, of the gas liquid chromatograph, the syringe was cleaned with glass distilled hexane or nanograde acetone. Analysis was done by a 7600 series Packard Gas Chromatograph. Results Various approaches were tried, attempting to identify the 3 main sugars of nectar isothermically in l97l. There were changes in the length and diameter of the glass columns, types of liquid phases on different types and sizes of column supports, oven temperatures (l350C- ZAOOC), and attenuation (3xlO-IO-lxl0-7) amps full scale. All were somewhat unsuccessful, therefore, a second approach was taken. It was found that a glass column 6 ft by l/h inch of 3% OV-l7 (5 ft) on G.C.Q. lOO/l20 mesh and l% 0V-l7 (l ft) on G.C.Q. mesh would separate the three main sugars of nectar at different temperatures at sensitivities of 1x10.8 and lxlO-9 amps full scale. Column temperature was l600 C. Fructose came off first at 3 min and 25 sec and glucose at 6 min and 5 sec with the sensitivity at lxlO-9 amps full scale. After glucose came off, the programmed temperature operation began, being controlled' automatically by the digital programmer. The temperature rose from 125 1600 C to 2200 C at a rate Of 9.90/min. With the rise in temperature, sucrose came off at approximately 25 min depending on the time that the digital programmer was started. This method was abandoned because of severe tailing on the sucrose peaks. By using the two different columns, (5% QF-l and l0% D.C. 200), the three main sugars found in nectar were successfully separated. Sucrose came off at 3 min, 20 sec with the 5% QF-l column. The l0% D.C. 200 column brought fructose off at ll min, 50 sec and l8 min l0 sec, whereas glucose came off at 16 min, 5 sec and 23 min, 25 sec. In 1973 it was found that a six foot x l/8 inch glass column of l% D.C. 200 on 60/80 mesh Gas Chrom 2 with the oven temperature pro- 0 C at a rate of lO-lSO/min and the N2 carrier at ID or 20 p.s.i. would separate the 3 main sugars found in nectar grammed from ISO0 - 220 when using the standard solutions. But the curves of the nectar samples did not coincide with those of the standards. Changes in column length, attenuation, type of column supports and size did not correct the situa- tion. Therefore, I went back to two different columns to separate the sugar derivatives as in l97l. Sucrose came off at 3 min, 42 sec with 1% D.C. 200 column. The combination column of l% and 3% 0V-l7 brought fructose off at 5 min, 45 sec. Glucose came off at 9 min, 53 sec and at l5 min, 7 sec. The nectar of cucumbers was found to be sucrose dominant, with Fructose predominating over glucose in all samples except one (Table A8). 0 .Overall, sucrose averaged 60.5tl.9%, fructose 25.ltl.2%, and glucose lh.htl.0% of the total sugars present. During l97l sucrose ranged from 126 39.7% - 59.3% with a mean of 51.8f3.0%. The values for I973 were higher, ranging from “3.1% - 78.9%, with a mean of 62.9t2.l%. Glucose ranged from 16.6% - 3.1?0 with a 213452.10 average in I97] and from 7.1% - 19.2% with a mean of 12.ht0.68% in I973. Fructose ranged from 2l.2% - 3l.3%, averaging 26.3tl.3% for l97l and 24.7tl.5% in I973 ranging from l3.6% - hl.0%. Nectar from pistillate flowers was slightly higher in sucrose and lower in glucose than from staminate flowers. Fructose was slightly lower in pistillate flowers but the difference was not significant (Table 49). Comparison of the five cultivars that were sampled during the two summers showed that all but one were similar in sugar composi- tion (Table 50). Spartan Progress which was sampled in l97l was signifi- cantly lower in sucrose at the 5% probability level (Student's t test) when compared to its nearest rival. Once the silylation reagent was added to the nectar sample, the sample was short lived. Within 2% hours a large change had taken place and the chromatograph curves could not be duplicated (Table SI). This was true when the samples were stored at room temperature, in the refrig- erator or in the freezer. Since the nectar samples were good only on the day they were silylated, many of our early samples in I97] became worthless in storage while we were working on methodology as explained in materials and methods. As a result all samples that were transported to the laboratory as flowers stored in a thermos bottle were lost. Freezing nectar immediately upon removal from the flower with dry ice looks to be the best method by the 197] data (Table 52). iii)‘ ll 127 emu..02u.e\o.002 uzm.00 xmoa m0 vommocnxo mo>2au 20m3m m.. « m.o0 0.. fi 0.:. «.. + ..m« ..020>o 0..« 0.00 0.0. .m. a. 0.. «.. «.0. m.m mm. u m« «.m« m.:0 m.m. «.« :.«. m.m mm« m.«« 0.0 00m 0 0N 0.00 ..0: 0.:. 0:. 0.0. 0.0 000 0..: 0.0. 000 z 0N 0.0. a.ma ..w «m «.m. :.m c:« a.mm «.0 .00 z «N a.mN m.m« ..«N MNN m.0 ..N m:. 0.m. w.m 0.N u .N ..:N 0.00 0.0. moN 0.0 :.N .N. 0.0. 0.0 0.N 2 0N m.«« 0.0m o.m. .m. «.N. m.« «ON 0.0m 0.0 0mm 0 m. :..m m.:0 :.m« .NN «.m m.« mo« m.0. ..m m0« 0 m. m.0N ..mm o.«. 00. m.0. m.m mm« 0.:« o.m «am 0 0. 0..N 0.0m m.«. m:. a.m. o.m m.N 0.0N «.0 mam z 0. «.0N 0.:m m.m. 0m. a.m. m.m :NN o.Nm m.0 m0: 0 m. o.0N 0.00 0.0. 00. «.m. ..0 «m« :.o« m.m ..m z 0. 0.00 0.0N N.0N oN ..0 0.0 maN ..0. 0.0 0N0 2 0. N.Nm m.o0 a.m. 0m. a.m. «.0 m0« 0.0N 0.0 000 0 N. m.N. m.00 0... m0. ..m. m.N 00m o.0N m.m 00m x .. ..mm :.:m 0.0. «m. w... m.m 00N a.mm N... cm0 0 o. 0.0. m.0m o.m 00 m.0. m.N mm. N.0N N.: 0:: z m 0.N: 0.00 «.NN 0NN N... 0.0 0N0 0..m 0.0. 000 2 m 0.0N m.N0 o.m. .m. N.m m.. mN. 0.0. 0.m o.« 0 0 N.MN N..0 0.0. «N. o... 0.N 00. m.N. ..0 0mN z 0 0.0N 0.00 m.N. :0. 0.0. N.0 moN ..mm m.N 000 2 0 w.m. N.m0 ..o. 0:. 0.0 ... cm. 0.0. 0.N MNN 0 0 0.0. 0.3 0... 0N ...0. 0.. 000 0.00 0.0 .N0 2 0 a.m. ...0 m.m. mm. m.m 0.. m0« 0.0N 0.: cm: x N 0... :..0 0.0 .o. a... m.. moN N.0N ..m 0mm 0 MNW . 00.0. m.mm 00.0 .Nm 0.0. 00.. 00 ..:N N0.N m.. 0 N. mm.m 0.0m m:.m mNN 0.0. 00.. .m N.:N 00.. N0 0 m. 00.0. N.00 0..: 000 ..00 00.0 N0. N.NN 00.N 0N. z a. :..0 m.wm N0.m mmN a.m. NN.. mm N..N 0m.. mm 2 0. 00.0 0.00 NN... 000 0.0. 0N. 00 0.0N 00.N 00. 2 .. mo.o« ..N: 00.0 mw0 0.wN m0.m o0N m.mN mw.m NON 0 m. 00.0. o..0 mm.N 000. 0.0. 00.N mN. m..m 00.: 00N 2 NM. . . Amem2mo2o.ev 20mjm 00 20me mo 20m00 wo 00msm mmo2osm 06020 o>23o 00003.0 08020 o>2ao omouun20 0&02m 0>23o .o: .0000 x uo2o.z mmo2oam N iO2o.z mmoo:.o N io2u.z 00o0o320 xom .0.> .co.u0.>..m mo >00 00a :0 20000: 200E:oau 0o co.u.manou 000 a .m: 0.000 l28 Table A9. - Percentages of sugars in nectar from staminate and pistillate cucumber flowers. _Ygfl 32% [1 z, Fructose f/g Glucose .72 Sucrose 1971 male 3 26.6 t 2.9 23.6 t 4.8 A9.9 t 5.6 1973 male 9 27.0 t 2.7 14.7 t 1.2 58.3 t 3.6 Overall 12 26.9 t 2.1a 16.9 t 1.8 56.2 t 3.2 1971 Female 6 26.1 f 1.2 20.7 t 2.7 53.2 t 3.9 1973 Female 16 23.5 t 1.8 11.0 t 0.6 65.5 t 2.3 Overall 20 24.0 t 1.5a 13.0 t 1.1 63.0 t 2.3 Overall means in each column followed by the same small letter are not significantly different at the 10% probability level (Student t test). Table 50. - Percentage of sugars in nectar from various cucumber cultivars. Cultivar fl .% Fructose .Z Glucose .Z Sucrose Spartan Progress 3 27.7 f l.9 22.8 f 5.l A9.h t 5.2 Piccadilly 9 26.9 t 2.7 l3.h f 1.0 59.6 f 3.l 35G x 38lG 6 2h.6 t 2.8 15.2 t 3.2 60.1 t 5.h 35G 6 22.7 t 2.3 l2.h f l.h 6h.9 t 3.2 SMR 58 8 2h.1 t 2.8 13.h f 1.7 62.5 t h.3 129 Samples that were placed in vials and not frozen had a lower percentage of sucrose with higher amounts of glucose and fructose. However, the 1973 values were the reverse of 1971. Statistical comparison of the overall values for the two methods, showed that they were not signifi- cantly different at the 5% probability level (Student's t test). It is possible that some change in the nectar could take place during transit in a warm car from the field to the freezer. Some atypical peaks came off in 1973 that were not present with the standards. Nine of the 25 samples had two small peaks come off at 2 min, 35 sec and 3 min, 3 sec, just prior to sucrose at 3 min, 42 sec. In looking at the nine samples involved, no definite trends could be found. All four of the cultivars used in 1973 were involved, with five samples coming from pistillate flowers and four from staminate. There- fore, pollen contaminants found in the nectar of staminate flowers could not be the cause. Six of the samples were quick frozen on dry ice and three brought to the laboratory in vials. Testing showed that the unknowns were not maltose since it came off with the 1% D.C. 200 column after sucrose at A min, #5 sec. The same nine samples also acted differently on the column used for separating glucose and fructose. The largest variations were in the second fructose curve of the standard. This curve only showed up with these nine samples and four variations of it were seen. Secondly, an unknown was found between the two glucose curves in all nine of the samples and peaked at 12 min, 2h sec. 130 0000020 0:0 >.co .00>23o 030 >..0E2o: 0N.0 0000 0. 000000 H II ‘0 _‘a ‘\ 200. ..o2u_E \mo.002 00m.00 x000 00 0000020X0 m0. 00003.0 2 m omm mm: 00003.0 02000000 0N. 00000320 0 m m0. 00000320 0 . JON 2am: 0000.032“. 0200:00m 0x000 oz 0002o3m 2 0 0x000 Oz 0mo2o3m 2 N awn 0002030 2 . 0 MON mom 000203m 0200000m mm 0.. :0. 0m 00003.0 2 N. 0N. w«. 00. m.. 00000322 2 N. mmm 0mm .Nm 0002030 0 N. 00>23u u:02000.0 ow: mw0 0mo2o3m 2 m. x00N 00N oo« 00003.0 2 m. .NON 000N mN0N 0086022 2 0. M00: 0..m 0000 0002030 2 0. m.. 0N. MN. 00003.0 z 0. 0.. mac. 0o« 00000322 2 0. .o: 0N .N 0. w 0 a 0 20030 X00 .0.> .002000000 000 00.0500 20000: 0000.>..m mo >0...0mum i ..m 0.000 l3] 0:02000.0 >.0:00.0.cm.0 00: 020 20000. ..0000 0 05003000 00>00 >0___nmno2a gm 0:0 00 ..050 0500 000 >0 0030..00 053.00 0000 c. 003.0> :005 ..020>o 0m.~ 0 m.00 00.. 0 0.0. 2.. 0 0.2N 0. 002 >25 00.0.0 0.m0 00.. a N.m_ 2.. 0 0.00 0. _m_> 0.020>o o.m 0 0.00 0.. 0 2.0. 0.0 0 0.20 __ 00_ >2o 0.0 0 0.00 0.0 0 m... 0.. 0 N.NN :. _m_> m20. m.m a m.mm 0.0 0 ..om 0.. 0 0.00 m 00_ >20 ..N w 0.0: 0.0 0 0.00 0.0 a 0.00 N _m_> .20_ 0002030 $ 00003.0 x 00000320 X 00000: 200> .>20002000. 000 00 00.0500 20000: 02.020000020 200 0000005 00 c00.200500 n .Nm 0.005 I32 Discussion As was pointed out in the literature, the chemical constituents are sometimes characteristic of the plant family as a whole. Cucumber nectar was found to be sucrose dominant with fructose and glucose present. This is similar to Percival's (1961) analysis of nectar from Luffa_ cylindrica and Momordica balsamina of the family Cucurbitaceae. Both the pistillate and staminate cucumber flowers produce a quality and quantity of nectar that must be considered relatively attractive to the honey bee based both on chemical analysis and observations of bee activ- ity in the field. Wykes (l952a) found that sugars which occur in nectar were not Vequally attractive to bees. Consistent preferences were shown for solu- tions of sugars in the following decending order: sucrose, glucose, maltose and fructose. The acceptance of both sucrose and glucose rela- tive to fructose was markedly high. Von Frisch (l93h) cited by Wykes (l952a) found that glucose and fructose were equally attractive to bees. He agreed that sucrose was the most attractive sugar as did Bailey, Fieger and Oertel (l95h). These results indicate that nectars contain- ing high percentages of sucrose might be more attractive to bees than nectars containing relatively low quantities of this Sugar. This could explain why cucumber nectar is relatively attractive to bees, since over half of the sugar present was sucrose. Percival (l96l) found that tsucrose predominated in the nectar of flowers visited by bumble bees, honey bees, butterflies and moths. Wykes (l952a) found consistent preferences for a mixture of equal proportions of sucrose, glucose and fructose, over solutions of 133 single sugars, mixtures of two sugars, or the same sugars available in different proportions. Furgala, Gochnauer 8 Holdaway (1958) noted that white sweet clover has this balance of the three sugars and found that bees preferred this nectar to that of alfalfa, alsike or red clover which are sucrose dominant. Flowers that are highly competitive for bee visits with the cucumber may have nectar containing the preferred balance of sugars. Since Percival (196]) found that nectars containing this preferred balance of sugars are uncommon, only #8 of 889 species sampled, it appears that the ratio of the three sugars may be an important aspect in monitor- ing the potential attractiveness of a crop to bees. Von Frisch (1950) found that the honey bee's threshold of accept- ance for sugar solutions was a 5% concentration, but varied with feeding conditions. If there are many plants in bloom, the threshold may be as high as 40%. Jamieson and Austin (l956).found that honey bees distin- guished differences of 5% in sugar syrup concentrations. Significantly more bees were attracted to 50% sucrose solutions than to #5 and h0% solutions. Bees were unable to distinguish between steps of SO,47.S and hS% sucrose solutions. Woodrow (1968) showed that bees preferred h0% and 50% sucrose solutions to more concentrated and less concentrated solutions. The discrimination against 60% concentration was distinct. Kropacova and Kr0pac (l968) found a significant positive correlation between the sugar concentration of chive nectar and bee visitation. 'They found that visitation was virtually independent of the quantity of nectar present. Butler (l9h5) concluded that nectar concentration was used by the bees to determine which plant species was preferred and I34 nectar quantity determines the proportion of the foraging population of the colony which will work those flowers. From these studies it would appear that the sugar concentration of nectar is very critical in deter- mining its attractiveness to the bee. However, Woodrow (l968) suggested that a wide variation in sugar concentration is acceptable to the bee since each bee load is ordinarily a composite accumulation of small quantities of nectar from several individual flowers. He suggested that sugar concentration alone at times may be less influential than other factors in the selection of plants by foraging bees. Along the same line of thought, Pedersen (l956) warned plant breeders that selections based on sugar concentration should be used cautiously because of the very pronounced effect of the environment on sugar concentration. If breeding efforts are made to maintain or improve the attractiveness to bees, of bee-pollinated crops, high sugar concentrations, larger quan- tities of nectar, preferred balance of sugars and possible modifications in flower structure may have to be considered. Nectar replacement is a rapid event (Chapter III) and with multi- ple visits throughout the day there is a large decrease in sugar concen- tration. ‘Woodrow (1968) found that the selection of the preferred con- centration occurred in the first few minutes of a test. That is, the honey bee determines whether the nectar is attractive or not on its initial visits to the flower. Even though the sugar concentration of cucumber nectar in the field may decrease throughout the day, making it less attractive to successive visitors, the bees continue to work the flowers due to their original attraction and foraging constancy. 135 Another phase of this work has shown that many plants competing with cucumber for bee visits have sugar concentrations higher than cu- cumber (unpublished) and many have preferred sugar mixtures Percival (l96l) and Furgala, Gochnauer 8 Holdaway (1958). Therefore, the presence of large acreages of such plants within flight range of bees located for cucumber pollination will reduce bee visits to the cucumber field and thus affect the efficient use of bees located for pollination of the crop. Plant breeders in the past, while developing many new strains 'of economically important plants, rarely considered nectar secretion when selecting desirable traits. If bee-pollinated crops become unat- tractive to bees or strains to be hybridized vary in attractiveness, pollination of the crop may become a real problem. Nectar volume can be measured and sugar concentration determined with reasonable accuracy using a hand refractometer, without much training, or expensive equip- ment. If the plant breeder felt it was desirable to know the composition of nectar, gas liquid chromatography seems to provide a suitable tech- nique. By knowing the nectar production characteristics of a plant, the plant breeder could select progeny, so the cultivars attractiveness would be maintained or improved, thereby improving competitive status of the crop and pollination. This work has shown that gas liquid chromatography is applicable to nectar research. With refinement of methodology, nectar samples could be run in a short time compared to various forms of paper chroma- tography, and reliable quantitative as well as qualitative data would I36 be available. Various avenues should be taken to refine the method used for nectar analysis. More work might turn up a column that would sepa- rate the sugars isothermically in a relatively short time. As shown, nectar samples and standards are short lived once the silylating reagent is added whether stored at room temperature, in a refrigerator or freezer. A better understanding is needed of what is taking place in the samples during the first 2A hours in relation to changes in peaks, stability and reliability. Other silylation reagents might be found that would prolong the life of the sample. Literature shows that nectar contains many materials, other than sucrose, fructose and glucose. Columns, silylating reagents and methods could likely be found so complete nectar analysis could be made if desired. Already columns and silylation methods have been developed to analyze amino acids, vitamins, alcohols, proteins, volatile organic oils and organic acids. Gas liquid chromatOgraphy is a practical method since nectar samples would only have to contain lO-lS mg of sugar per sample. This is important since many flowers are structured so that large samples are impossible to obtain. Samples could be collected during the day, quick frozen in dry ice in the field, then frozen and lyophilized in the laboratory for later silylation and analysis. SUMMARY AND CONCLUSIONS 1. In both staminate and pistillate cucumber flowers, nectar was the primary attractant. Few bees were observed collecting pollen. The pellets of those observed collecting pollen were small in size com- pared to the pellets from major pollen sources. 2. All cucumber cultivars tested in this study produced a quan- tity and quality of nectar that was attractive to honey bees. New cultivars may have a higher nectar secretion potential because of the swing to gynoecious F] hybrids which have predominantly pistillate flowers. 3. The nectaries of staminate and pistillate flowers differ in both shape and size. The nectary of the pistillate flower is in the form of a cup surrounding the base of the style, whereas the nectary of the staminate flower is a three-lobed button lying on the floor of the receptacle. The nectary of the pistillate flower is l.6 - l.9 times as wide as that of the staminate flower and it has approximately twice the secretory surface. Most nectaries of staminate flowers are 2 to 3 mm wide, whereas those of pistillate flowers are A to 5 mm. A. The epidermal layer on the surface of the nectary contains stomate-like pores that appear to open and close as the environment around them changes. The stomate-like pores are found only on the inner surface of the nectary of the pistillate flower but in staminate 137 l38 flower nectaries they are found on the upper surface and outer edge. The nectary surface is irregular and the area surrounding the stomates appears to be slightly depressed. 5. Typically the nectary of a staminate flower is a three-lobed structure, though on occasion four-lobed nectaries may be observed. Populations of the various cultivars contained from 0.7 to 12.3% four- lobed nectaries and the trait appeared to be environmentally influenced in the greenhouse. 6. Positive correlations were consistently found comparing nectary width with petal diameter, volume of nectar, total weight of sugar present, and ovary length, but not sugar concentration. 7. Basically the cucumber flower has a one day secretory cycle with maximum secretion on the day of anthesis. Flowers secrete no nectar in the bud stage. Less than l/3 of the second day flowers contained nectar and only about 3% of the third day flowers. Flowers on the day of anthesis produced l.l times more nectar than the one day old flowers and 3.8 times that of the two day olds. The actual weight of sugar in the nectar showed even a greater reduction due to large decreases in sugar concentration. Flowers on the day of anthesis con- tained 2.5 times more sugar than one day olds and ll.6 times that of two day old flowers. 8. The commencement of nectar secretion appeared to be tempera- ture dependent.> Below 160 C nectaries were dry on the day of anthesis. At l6o C they began to look moist under the microscope. At 170 C, l-2 small beads of nectar began to form on the inner surface of the cup 139 of the pistillate flower and by time the temperature reached BIO C, the first measurable amounts of nectar were collected. 9. Nectar in individual flowers varied under different condi- tions throughout the day from none to over 30 ul in amount, from l3% - 60% in sugar content and from O to l2.33 mg of sugar when bees were ex- cluded from the flowers. l0. Throughout the day, without bee visitation, the average volume of nectar and total weight of sugar increased and sugar concen- tration decreased. ll. The sugar concentration of nectar was greatly reduced ”re- absorbed” during the night but the volume of nectar remained about the same. The nectar of pistillate flowers went from 34.8% to l2.0% sugar and from Al.2% to l8.9% in staminate flowers. Comparable decreases were also found in the actual weight of sugar present. l2. The secretory rhythms of staminate and pistillate flowers were similar but differed in content. Pistillate flowers produced ap- proximately l.5 - 2.3 times as much nectar as staminate flowers but staminate flower nectar had a higher sugar concentration (h5.3% com- pared to 36.3% in one study). The total weight of sugar for both types of flowers was generally quite close, with pistillate flowers having a slight edge. 13. Honey bees must visit more staminate than pistillate flowers to obtain an equal amount of nectar. Even though this requires a greater energy expenditure, the bee is rewarded about equally by stamin- ate flowers because they have a higher concentration of sugar. This helps to insure that both pistillate and staminate flowers will be visited and pollination result. lhO l4. In the field, bees spent almost twice as long per visit on pistillate flowers as on staminate flowers. When honey bees reach down to the nectary, they automatically come in contact with the anther or stigma, so that pollination results. The length of the visit depends on the amount of nectar present. Since pistillate flowers produce from l.5-2.3 times more nectar than staminate flowers, it takes the bee al- most twice as long to collect it. If the honey bee is not disturbed, it will remove all of the nectar present in one visit. l5. Nectar replacement in a flower is a rapid event. Some nectar is replaced within 5 minutes after removal. Six hourly removals from the same flowers showed that the flower can replace approximately the same volume of nectar that was removed the hour before but the sugar concentration and actual weight of sugar decreased sharply. Multiple visitation or nectar removal did not stimulate nectar production. 16. With bees excluded, the mean sugar concentration of nectar taken from both types of flowers was 40.8%. On the other hand the mean sugar concentration of nectar removed from the honey stomachs of bees gathering from cucumbers in the same field was 24.5%, showing a h0% difference in sugar concentration. The difference is largely explained by reduced concentration due to nectar removal and replacement. l7. To accurately compare nectar secreting characteristics of different cultivars, data for staminate and pistillate flowers had to be considered separately due to their secretion differences. No signifi- cant differences were found in the cultivars compared. On a field basis, cultivars that produced predominantly pistillate flowers secreted larger lhl volumes of nectar with more total sugar than staminate lines which pro- duced nectar with higher average sugar concentrations. l8. There tended to be slight increases in flower size, nectary size and volume of nectar in flowers produced further down the vine from the base. 19. Flowers found on lateral vines tended to produce a larger quantity of nectar containing a higher weight of sugar than those on main vines. 20. Only morning pollinations affected nectar secretion. From the time of pollination in the morning to fertilization the cucumber flower continues to secrete nectar and replenish its supply after each visit. After fertilization nectar secretion appeared to cease. Any nectar remaining in the flower may be changed in water content depending on the relative humidity and be partially reabsorbed during the night. 2l. Attempts to identify the three main sugars of nectar isother- mically with gas liquid chromatography were unsuccessful. Therefore, the three sugars in the nectar samples were quantified with two differ- ent columns. 22. Once the silylation reagent (Tri-Sil Z) was added to nectar, the samples changed quantitatively. Within 2A hours a definite change had taken place and chromatograph curves could not be duplicated. This was found to be true regardless of whether samples were stored at room temperature, in the refrigerator, or in the freezer. 23. The nectar of cucumbers was found to be sucrose dominant, with fructose predominating over glucose. Sucrose averaged 60.5%, fructose 25.l% and glucose lh.h% of the total sugars present. lhz 24. Unknown peaks were found in nine of the nectar samples. Two appeared prior to sucrose at 2 min, 35 sec and 3 min, 3 sec and one between the two glucose curves at l2 min, 24 sec. 25. Since the cucumber flower basically secretes for only one day, factors that prevent bees from flying, essentially prevent pollina- tion of that days flower output. Gaps in flower pollination lessen uniformity of pickle production for machine harvest. However, the sugar supply of unvisited flowers may still be potentially available to the bee at a later time due to reabsorption and resecretion. 26. Both pistillate and staminate cucumber flowers were found to produce a quality and quantity of nectar that must be considered relatively attractive to the honey bee, based both on chemical analysis and observations of bee activity in the field. However, in comparing sugar concentration and total weight of sugar with major nectar sources, cucumbers would rate moderately attractive but because of a relatively small number of flowers per acre, it cannot be rated as an important honey plant. 27. When bee visits and pollination were delayed to flowers on later nodes, flowers gave greater rewards to visiting bees, pollination was more effective and fruit yield was of a higher quality. This could be because the cucumber flower reabsorbs its uncollected sugar supply, so the plant was able to build up larger carbohydrate supplies for nectar production through a longer period of photosynthesis and reab- sorption before collection. 1&3 28. These studies indicate that important factors of attractive- ness of a crop to bees could be readily monitored during a plant breed- ing program. The volume of nectar and total weight of sugar in the nectar appear to be the best indicators. Nectar volume can be measured and sugar concentration determined with reasonable accuracy using a hand refractometer without a great deal of training, consumption of time, or expensive equipment. These values could also be supplemented with measurements of the nectary and analysis of honey stomach contents from bees working the crop. If maintenance or improvement in the attractive- ness to bees of bee-pollinated crops is to be considered in a crop breed- ing program, higher sugar concentrations, larger quantities of nectar, preferred balance of sugars within the nectar and possible modifications in flower structure appear to be factors of greatest significance which may be reasonably monitored. 29. Any significant increases in quantity and quality of nectar produced, for both staminate and pistillate cultivar lines of cucumbers, would help to lessen the competition that exists between the cucumber and other nectar sources in the area of the field. 30. Average analysis of cucumber nectar: Water - 59.2% Sucrose - 24.7% Fructose - lO.2% Glucose - 5.9%. LITERATURE CITED . I lilllt. Ill" Ill-III! llllllltll \ 8" I]! Illl: LITERATURE CITED Agthe, C. I95]. The physioIOgical origin of plant nectars. Promotion- sarb. E.T.H., Zurich No. 20l7: 240-74. Abstract seen in Apic. Abst. 36/52. Association of Official Agricultural Chemists. I950. Official Methods of Analysis. 7th ed. Washington, D.C. Bailey, M. E., Fieger, E. A., Oertel, E. I954. Paper chromatographic analysis of some southern nectars. Glean. Bee Cult. 82: 401-3, 472-4. Baker, L. R. I972. Associate Professor, MSU Hort. Dept., East Lansing, Michigan. Personal Communication. Banadyga, A. A. I949. Cucumbers For Pickles. Nat. Pickle Packers Assoc., Oak Park, Ill. Barbier, E. C. I962. Some factors in the quantitative and qualita- tive productivity of essential oils from lavendar (Lavandula) Ann. Abeille 5(4): 265-379. Abstract seen in Apic. Abst. 335/64. ' Beutler, R. I953. Nectar. Bee World, 34: 106-16., l28-36, l56-62. Bohart, G. E., Nye, W. P., Hawthorn, L. R. I970. Onion Pollination as Affected by Different Levels of Pollinator Activity. Utah Agr. Exp. Sta. Bull. 482 57 PP. Bohn, G. W. I96I. Inheritance and origin of nectarless muskmelon. J. Hered. 52(5): 223-37. Bohn, G. W., Mann, L. K. I960. Nectarless, a yield-reducing mutant character in the muskmelon. Proc. Amer. Soc. Hort. Sci. 76: 455“9. Brett, C. H., Sullivan, M. J. I972. Bee Attraction to Cucurbit Flowers and Pollination. N. Carolina State Agr. Exp. Sta. Bull. 443, 22 pp. Browne, C. A. I908. Chemical Analysis and Composition of American Honeys. Bull. U. S. Bur. of Chem. IIO. I45 I46 Butler, C. G. I945. Influence of various physical and biological factors of the environment on honey bee activity. An ex- perimentation of the relationship between activity and nectar conc. and abundance. J. Exp. Biol. 2]: 5-I2. Butler, G. 0., Jr., Loper, G. M., McGregor, S. E., Webster, J. L. and Margolis, H. I972. Amounts and kinds of sugars in the nectars of cotton (Goss pium spp.) and the time of their secretion. Agron. J. 6i 5, : 364:8. Callis, A. I926. Composition and changes in nectar. Amer. Bee J. 66:226-7. Chakravarty, H. L. I958. Morphology of the staminate flowers of the Cucurbitaceae with special reference to the evolution of the stamen. Lloydia 2I:49-87. Cirnu, I., Tone, E., Coteanu, 0. I967. The dynamics of nectar secre- tion in Cucurbita maxima Dutch Proc. XXlst Int. Apic. Congr., Univ. Md., p. 483. Collison, C. H., Martin, E. C. I970. Competitive plants that may affect the pollination of pickling cucumbers by bees. Amer. Bee J. IIO:262. Connor, L. J. I969. Honey Bee Pollination Requirements of Hybrid Cucumbers Cucumis sativus L. Mich. State Univ. M.S. Thesis. Connor, L. J., Martin, E. C. I970. The effect of delayed pollination on yield of cucumbers grown for machine harvests. J. Amer. Soc. Hort. Sci. 95: 456-8. Connor, L. J., Martin, E. C. I97I. Staminate-pistillate flower ratio best suited to the production of gynoecious hybrid cucumbers for machine harvest. Hort. Science 6:337-9. Cook, W. S. I923. The structure of some nectar glands of Iowa honey plants. Iowa Acad. Sci. Proc. 30: 3OI-29. Cotti, T. I962. Quantitative measurement of phosphatase activity in nectaries. Ber. Schweiz. Bot. G05. 72: 306-32. Abstract seen in Apic. Abst. 305/65. Czarnowski C. von. I952. Researches on the problem of nectar secre- tion. Arch. Geflugelz. Kleintierk. I(I): 23-44. Abstract seen in Apic. Abst. IOI/53. Davidson, J. I922. Factors affecting nectar secretion in flowers. Amer. Bee J. 62: I53-4. 1 ll ’I‘IIII 1' IIIIIII I47 Demuth, G. I923. Temperature and nectar secretion. Glean. Bee Cult. 5I: 582.. Edgecombe, S. W. I946. Honey bees as pollinators in the production of hybrid cucumber seed. Amer. Bee J. 86: I47. Esau, K. I953. Plant Anatomy. N.Y., John Wiley 8 Sons Inc., pp. 557-8. Faegri, K., vander Pijl, L. I966. The Principles of Pollination Ecology. London: Pergamon. 248 pp. Fahn, A. l949a. Nectaries of honey plants in Isreal. Paisst. J. Bot. Jerusalem Ser. 4: 207-24. I949b. Studies in ecology of nectar secretion. Palest. J. Bot., pp. 207-24. . I952. On the structure of floralnectaries. Bot. Gaz. II3(4): 464-70. Feltner, K. C., Sackett, R. G. I964. Effect of 2, 4, 5 trichlorophenoxy- acetic acid on quantity and composition of nectar and seed production of alfalfa, Medicago sativa L. Crop Sci. 4: 560-2. Findlay, N., Mercer, F. V. I97I. Nectar production in Abutilon. ll. Submicroscopic structure of the nectary. AustaI. J. Biol. Sci. 24: 657. Foster, R. E., Levin, M. D., McGregor, S. E. I965. Nectar production by muskmelons infected with four mosaic viruses. Proc. Amer. Soc. Hort. Sci. 86: 433-5. Free, J. B. I970. Insect Pollination of Crops. London: Academic. 544 pp- Free, J. B., Durrant, A. J. I966. The dilution and evaporation of the honey stomach contents of honey bees at different temperatures. J. Apic. Res. 5: 3-8. Frey-Wyssling, A., Agthe, C. I950. Nectar is secreted phloem sap. Verh. Schweiz. Naturforsch. Gesellschaft I30 Versammlung, Davos. I75-6. Abstract seen in Apic. Abst. 35/52. Frey-Wyssling, A., Zimmermann, M., Maurizio, A. I954. Enzymatic sugar conversion in nectaries. Experientia IO(I2): 490-2. Abstract seen in Apic. Abst. 278/55. Frey-Wyssling, A., Hausermann, E. I960. Interpretation of nectaries with no differentiated shape. Ber. Schweiz. Bot. Ges. 70: ISO-62. Abstract seen in Apic. Abst. 3/65. I48 vonFrisch, K. I950. Bees: Their Vision, Chemical Senses and Language. Ithaca, N.Y.: Cornell Univ. Press. l57 pp. Furgala, B., Gochnauer, T. A., Holdaway, F. G. I958. Sugars of some northern legume nectars. Bee World 39: 203-5. Gary, N. E., Witherell, P. C., Marston, J. I972. Foraging range and distribution of honey bees used for carrot and onion pollina- tion. Environmental Entomol. I: 7I-8. Hayward, H. E. I938. Structure of Economic Plants. MacMiIIan Co. Chapter IV. Helmlich, H. F. I927. The development and anatomy of the staminate flower. Amer. Jour. Bot. 14: 227-37. Heinrich, 8., Raven, P. H. I972. Energetics and pollination ecology. Science. l76(4035): 597-602. Honey Market News. I973. Consumer and Market Serv. U. S. Dep. Agr. 57(4): 8. Hopkins, C. Y., Jevans, A. W., Boch, R. I969. Occurrence of octadeca- trans-Z, cis-9, cis-IZ-trienoic acid in pollen attractive to the honey bee. Can. J. Biochem. 47: 433-6. Huber, H. I956. Effect on nectar secretion of temperature and the moisture content of air and soil. Planta 48: 47-98. Abstract seen in Apic. Abst. 266/59. lfteni, L. I967. Structure of floral nectaries and nectar production in some melliferous Species. Proc. XXIst. Int. Apic. Cong. Univ. Md. 454-9. Jamieson, C. A., Austin, G. H. I956. Preference of honey bees for sugar solutions. Tenth Int. Cong. Entomol. Proc. Montreal. 4: 1059-62. Jaycox, E. R., I970. Ecological relationships between honey bees and soy- beans. Amer. Bee J. IIO: 306-7, 343-5, 383-5. Judson, J. E. l929a. The morphoIOgy and vascular anatomy of the pistillate flower of the cucumber. Amer. Jour. Bot. l6: 68-89. I929b. The floral development of the staminate flower of the cucumber. Papers Mich. Acad. Sci. 9: I63-8. I935. Floral development of male flowers of the honey rock muskmelon. Proc. West Va. Acad. Sci. 8: 93-8. la. .‘llll’llll I I49 . I949. The pistillate flower of the muskmelon. Proc. West Va. Acad. Sci. 20: 79-84. Kartashova, N. N., Novikova, T. N. I964. Chromatographic study of the chemical composition of nectar. Izv. tomsk. Otd. vses. bot. Obshch. 5: III-l9. Abstract seen in Apic. Abst. 538/67. Kauffeld, N. M., Williams, P. H. I972. Honey bees as pollinators of pickling cucumbers in Wisconsin. Amer. Bee J. II2(7): 252-4. Kaziev, I. P., Seidova, S. S. I965. The nectar yield of flowers of some Cucurbitaceae under Azerbaidjan conditions. XX Int. Beekeeping Jubilee Congr. II: 3], 364-6. Kenoyer, L. A. I9I6. Environmental Influences of Nectar Secretion. Iowa State College Res. Bull. 37, pp. 2I9-32. I9I7. Environmental influences on nectar secretion. Bot. Gaz. 63:249-65. Kirkwood, J. E. I905. Comparitive embryology of the Cucurbitaceae. Bull. N.Y. Bot. Gard. 3: 313-402. Kleinschmidt, M. G., Dobrenz, A. K., McMahon, V. A. I968. Gas chromatography of carbohydrates in alfalfa nectar. Plant Physiol. 43: 665-7. Knuth, P. I908. Handbook of Flower Pollination. Oxford, ll: 454-8. Koreshkov, V. M. I967. Secretion of nectar by extrafloral nectaries of the field bean, Vicia faba. Vest. nauchno-issled. Inst. Pchel. I5: 40-57. Abstract seen in Apic. Abst. 730/69. Kropacova, S., Kr0pac,A. I968. Importance of the chive, Allium schoenoprasum L., as the source of nectar. Sb. vys. Sk. zemed. Brne I6(2): 263-9. Abstract seen in Apic. Abst. 507/69. Livtzeva, E. K. I954. Methods used in nectar secretion investigations. Pchelovodstvo II: 33-9. Abstract seen in Apic. Abst. I96/55. Luttge, U. l96I. The composition of nectar and the mechanism of its secretion I. Planta 56: I89—2l2. Abstract seen in Apic. Abst. I29/64. I962. The composition of nectar and the mechanism of its secretion III. The role of resorption and the secretion of specific sugars. Planta 59: I75-94. Abstract seen in Apic. Abst. I3l/64. I50 McGregor, S. E. I973. Insect poIIination--significance and research needs. Rep. Beekeeping Ind. Conf., USDA Agr. Res. Center, Beltsville, Md. The Indispensable Honeybee Feb. I2 8 I3, 73. McGregor, S. E., Todd, F. E. I952. Cantaloupe production with honey bees. J. Econ. Entomol. 45: 43-7. McLean, D. M. I947. Stamen morphology in the flowers of the muskmelon. J. Agr. Res. 74: 49-54. Maksymiuk, I. I958. Nectar secretion in winter rape. Pszczel. Zesz. Nauk 2(2):49-54. Abstract seen in Apic. Abst. 851/64. Mann, L. K. I953. Honey bee activity in relation to pollination and fruit set in the cantaloupe, Cucumis melo L. Amer. J. Bot. 40:545-53. Martin, E. C., McGregor, S. E. I973. Changing trends in insect pollina- tion of commercial crops. Ann. Rev. of Entomol. I8: 207-26. Maurizio, A. I954. Secretion of nectar in polyploid plants. VIII Congr. int. Bot. Sec. IO: 2I6. Abstract seen in Apic Abst. 295/55. . I96l. Observations on the nectar of some Swiss and Swedish strains of red clover. Z. Bienenforsch. 5(7): l82-90. Abstract seen in Apic. Abst. 654/62. MeIinichenko, A. N. I963. Bees themselves increase the nectar produc- tivity of flowers. Pchelovodstvo 40(9): 32-5. Abstract seen in Apic. Abst. 566/65. Meyerhoff, G. I958. Behavior of bees foraging on rape. Leipzig. Bienenztg. 72(6): I64-5. Abstract seen in Apic. Abst. 89/60. Milum, V. G. I943. Illinois Honey and Pollen Plants. Mimeo Dept. of Entomol., Univ. III. Montgomery, B. E. I958. Preliminary studies of the composition of some Indiana nectars. Proc. Ind. Acad. Sci. 68: I59-63. Nenirovich-Danchenko, E. N. I964. Concerning the nectar yield and floral biology of cucumbers. Izv. tomsk. Otd. vses. bot. Obshch. 5: I27-32. Abstract seen in Apic. Abst. 54I/67. Nye, W. P., Pedersen, M. W. I962. Nectar sugar concentration as a measure of pollination of alfalfa, Medicago sativa L. J. Apic. Res. I: 24-7. 151 Nye, W. P., Waller, G. D., Waters, N. D. 1971. Factors affecting pollination of onions in Idaho during I969. J. Amer. Soc. Hort. Sci. 96: 330-2. Oertel, E. I946. Effect of temperature and relative humidity on the sugar concentration of nectar. J. Econ. Entomol. 39: 513-5. 1956. Nectar production by white clover. Glean. Bee Cult. 84: 461-3. 1967. Nectar and pollen plants. Agric. Handbk. U. S. Dept. Agric. No. 335: IO-l6. Pankratova, N. M. I950. Investigations on the process of nectar secretion. Zh. obshch. Biol. II: 292-305. Abstract seen in Apic. Abst. 93/52. Park, 0. W. 1932. New methods applied to studies on the sugar content of nectars. J. Econ. Entomol. 25(4): 826-32. 1954. How bees make honey. Amer. Bee J. 94(8):296-8,309. Paurtallier, V. J. 1968. Use of gas chromatography for the determina- tion of sugars in honey. Zeitschrift Fuer Bienenforschung. Nuremberg. 9(5): 217-22. Pedersen, M. W. I953b. Environmental factors affecting nectar secre- tion and seed production in alfalfa. Agron. J. 45(8): 359-61. 1956. Nectar production in relation to seed production in alfalfa. l0th Int. Congr. of Entomol. Aug. 17-25. Pedersen, M. W., Todd, F. E. I949. Selection and tripping in alfalfa clones by nectar collecting honey bees. Agron. J. 41(6): 247-9. Pedersen, M. W., LeFevre, C. W., Wiebe, H. H. I958. Absorption of Cl"1 labeled sucrose by alfalfa nectaries. Science 127:758-9. Percival, M. S. 1946. Observations on the flowering and nectar secre- tion of Rubus fruticosus. Agg. New Phyto. 45: III-I23. I961. Types of nectar in Angiosperms. New Phytol. 60: 235- 81. 1965. Floral BioIOgy. Oxford: Pergamon, 243 pp. Peterson, C. E. I960. A gynoecious line of cucumber. Mich. Agr. Exp. Sta. Quarterly, Bull. 43: 40-2. I52 Peterson, C. E., Anhder, L. 0. I960. Induction of staminate flowers on gynoecious cucumbers with Gibberellin A Science 131: 1673-4. 3' Raw, G. R. 1953. The effect on nectar secretion of removing nectar from flowers. Bee World. 34(2):23-5. Ribbands, C. R. I953. The Behaviour and Sociel Life of Honeybees. London: Bee Research Assoc. Ltd. 352 pp. Sanduleac, E. V. 1959. Data on the entomophilous pollination and the selection of Cucurbitaceae. Lucr. sti. Stat. Cemt. Seri. Apic. I: 129-32. Abstract seen in Apic. Abst. 43l/6I. Schnephf, E. I964. Cytology and physiology of plant glands. 5. Electron microscopy of cyathial nectaries of Euphorbia pulcherrima in relation to function. Protoplasma 58(2): I93-219. Abstract seen in Apic. Abst. 30I/69. Scullen, H. A. I940. Relative humidity and nectar concentration in ' fireweed. J. Econ. Entomol. 33: 870-1. 1942. Observations on the relationship of alsike clover nectar to the relative humidity. J. Econ. Entomol. 35: 453-4. Seaton, H. L., Dremer, J. C. I939. The influence of climatological factors on anthers and anther dehiscense in the cultivated cucurbits. A preliminary report. Proc. Amer. Soc. Hort. Sci. 36: 627-31. Shaw, F. R. 1953. The sugar concentration of nectar of some New England honey plants. Glean. Bee Cult. 8l: 88-9. Shaw, F. R., Farr, T. H., Goldstein, H. L. 1953. Sugar concentration of some Massachusetts honey plants. J. Econ. Entomol. 46(3): 521-4. Shuel, R. W. I952. Some factors affecting nectar secretion in red clover. Plant Physiol. 27: 95-IIO. I955a. Nectar secretion. Amer. Bee J. 95(6): 229-34. 1955b. Nectar secretion in relation to nitrOgen supply, nutritional status and growth of the plant. Canada J. Agr. Sci. 35: 124-38. I956. Studies of nectar secretion in excised flowers I. The influence of cultural conditions on quantity and composi- tion of nectar. Canada J. Bot. 34: 142-53. I53 I961. Influence of reproductive organs on secretion of sugars in flowers of Streptosolen jamesonii, Miers. Plant Physiol. 36(2): 265-71. . I964. Nectar secretion in excised flowers. III. The dual effect of indolyI-3-acetic acid. J. Apic. Res. 3(2): 99-111. 1968. Professor, University of Guelph, Guelph, Ontario, Canada. Personal communication. Shuel, R. W., Pedersen, M. W. 1953. The effect of environmental factors on nectar secretion as related to seed production. Proc. 6th Int. GrasId. Congr. 868-87I. Simpson, J. 1964. Dilution by honeybees of solid and liquid food containing sugar. J. Apic. Res. 3: 37-40. Skirde, W. I960. Methods for quantitative nectar determination in red clover. Z. Acker-u. Pfl Bau. |II(3): 2I7-36. Abstract seen in Apic. Abst. 655/62. Skirde, W. l96l. Methods for quantitative nectar determination in red clover. Z. Acker-u. Pfl Bau 113(2): l65-80. Abstract seen in Apic. Abst. 656/62. Swanson, C. A., Shuel, R. W. 1950. The centrifuge method for measur- ing nectar yield. Plant Physiol. 25: 5I3-20. Sweeley, C. C., Bentley, R. B., Makita, M., Wells, W. W. 1963. Gas liquid chromatography of trimethylsilyl derivatives of sugars and related substances. J. Amer. Chem. Soc. 85: 2495-507. Tiedjens, V. A. I928. The relation of environment to shape of fruit in Cucumis sativus L. and its bearing on the genetic potenti- alities of the plants. J. Agr. Res. 36: 795-09. ‘Timenskii, P. I. 1968. Fruit trees and bees. Pchelovodstvo. 88(1): 18-I9. Abstract seen in Apic. Abst. 305/69. USDA, 1968. Using Honey Bees To Pollinate CrOps, Leaflet 549. Vansell, G. H. I929. Sugars in nectar. Glean. Bee Cult. 57: 92-3. 1934. Relation between nectar concentration in fruit blossoms and visits of honey bees. J. Econ. Entomol. 27(5): 943-45. 1941a. Nectar and Pollen Plants of California. Univ. of Calif. Agr. Exp. Sta. Bull. 517. 154 1942. Factors Affecting the Usefulness of Honey Bees in Pollination. USDA Cir. 650. . I944a. Cotton nectar in relation to bee activity and honey production. J. Econ. Entomol. 37: 528-30. I944b. Some western nectars and their corresponding honeys. J. Econ. Entomol. 37(4): 530-3. 1952. Variations in nectar and pollen sources affect bee activity. Amer. Bee J. 92(8): 325-6. Waddle, B. A. 1970. The nectaries of cotton. Rep. Pollination Conf. Univ. Ark. 9th M.P. 127: 25-7. Watkins, W. L. 1926. Nectar producing resources of Michigan. Apiary Inspection Service, Dept. Agr. Bull. 4. White, J. W. Jr., Riethof, M. L., Subers, M. H., Kushmir, I. 1962. Composition of American Honeys. Agr. Res. Service, USDA, Tech. Bull. 1261. Wilson, W. T., Moffett, J. 0., Harrington, H. D. 1958. Nectar and Pollen Plants of Colorado. Colorado State Univ. Exp. Sta. Bull. 5035. Woodrow, A. W. 1968. Some factors affecting selection of sucrose solutions by foraging honey bees. Amer. Bee J. 108: 313-5. Wykes, G. R. 1950. Nectar secretion researches. Austral. Beekpr. 52(2): 67-68. Abstract seen in Apic. Abst. 37/51. 1951a. Some aspects of nectar secretion. 14th. Int. Beekeep. Cong. Paper. 1. Abstract seen in Apic. Abst. 184/51. I951b. The preferences shown by honey bees for certain nectars. Ann. App. Biol. 38(2): 546. Wykes, G. R. I952a. The preferences of honey bees for solutions of various sugars which occur in nectar. J. Exp. Biol. 29(4): 511-18. I952b. An investigation of the sugars present in the nectar of flowers of various species. New Phytol. 51(2): 210-15. I952c. The influence of variations in the supply of carbo- hydrate on the process of nectar secretion. New Phytol. 51(3): 294-300. 155 Yakovleva, L. P. 1966. Some problems concerning methods of assesing the nectar productivity of entomophilous plants. Trudy nauchno-issled. Inst. Pchel. 301-39. Abstract seen in Apic. Abst. 726/69. Zieglar, H. 1955. Phosphatase activity and oxygen consumption of the nectary of Abutilon striatum. Natur wissenschaften. 42(9): 259-60. Abstract seen in Apic. Abst. 358/60. Zieglar, H., Luttge, U. 1959. The resorption of Cl“ glutamic acid by secreting nectaries. Naturwissenschaften 46(5): 176-77. Abstract seen in Apic. Abst. 29/61. Zimmermann, M. 1953. Investigations of sugar secretion in plants, by means of paper chromatography. Ber. schweiz. bot. Ges. 63: 402-29. Abstract seen in Apic. Abst. 95/54.