PROPAGATION AND CULTURAL REQUIREMENTS OF PRINSEPIA (PRINSEPIA SINENSIS (OLIV.) OLIV. EX BEAN) Dissertation for the Degree of Ph. D. MICHIGAN STATE UNIVERSITY DAVID JAMES BEATTIE 19,77 ii-.:I........ . _ ¢_' - Iii—1;..Zivl 1'.” {23*} -n.‘ _ 13.. . .mY I-. f 1:313 State . University This is to certify that the thesis entitled Propagation and Cultural Requirements of Prinsepia (Prinsepia sinensis (Oliv.) Oliv. EX Bean) presented by David James Beattie has been accepted towards fulfillment of the requirements for Ph. D. degree in Horticulture fiat/M a Major pr fesso Date W11— 0-7639 ABSTRACT PROPAGATION AND CULTURAL REQUIREMENTS OF PRINSEPIA (PRINSEPIA SINENSIS (OLIV.) OLIV. EX BEAN) BY David James Beattie Section I: Germination of Prinsepia (Prinsepia sinensis (Oliv.) Oliv. EX Bean): Effects of Stratifi- cation Time, GA Treatment, Temperature and Post Germination Chilling Fresh or dry stored Prinsepia sinensis seeds with intact endocarp germinated satisfactorily although slowly, and chilling of seeds did not promote germination. Pro- longed stratification decreased germination. However, if endocarps were removed from seed that had been stratified for 4 and 8 weeks and then had failed to germinate after 8 weeks, germination was complete within 2 weeks when seeds were held in the dark. GA3 (100 or 500 ppm) hastened ger— mination of seeds in the endocarp but did not increase final germination. Optimum germination temperature was 20°; ger— mination was significantly lower at 150 and was practically nil at 25°C. Regardless of germination temperature, low temperature stratification, or the presence or absence of cotyledons, all seedlings were dwarf—rosetted in growth habit. Normal shoot elongation was restored only when seedlings were chilled for 14 or 21 days. While chilling slightly increased the number of leaves (nodes) per plant, David James Beattie the most noticeable effect of chilling was the marked increase in internode length. Scanning electron micro- scope examination of apical meristems showed limited de- velopment regardless of chilling. The presence of leaf primordia appeared to be of little importance in the re- sumption of normal shoot elongation. Section II: Germination of Prinsepia (Prinsepia sinensis (Oliv.) Oliv. EX Bean): Interaction of Light, Seed Coat, and Temperature Germination of prinsepia seed was inhibited by light. The effect was proportional to duration of light exposure after imbibition and decreased as time exposure was delayed. Photoreversible phytochrome was detected spectrophotometri- cally in etiolated seedlings, but not in imbibed seeds. Partial removal of seed coat increased percent germination and germination index in light; removal of the chalazal end was more effective than removal of the radicle end. Opti— mum germination temperature was 20°C in both light and dark- ness. Holding seeds at 100 for l to 2 weeks before transfer to 200 markedly reduced germination, while holding at 25°C did not. Section III: Influence of Chilled and Nonchilled Scions and Rootstocks in Prinsepia (Prinsepia sinensis (Oliv.) Oliv. EX Bean) Buds of nonchilled scions of Prinsepia sinen51s were induced to grow when grafted on chilled rootstocks, and David James Beattie growth of chilled buds was depressed by grafting on nonchilled rootstocks. Nonchilled dwarf—rosetted scions grew when grafted on chilled rootstocks, but failed to grow when grafted on nonchilled rootstocks. These re- sults suggest either the presence of a graft translocated stimulus, or lack of an inhibitor, of root origin that effects bud break. Section IV: Effect of pH Regimes and N-Fertilization on Growth of Prinsepia (Prinsepia sinensis (Oliv.) Oliv. EX Bean? Container grown plants of Prinsepia sinensis were supplied with 4 levels of nitrogen at media pH's of 4, 6, and 8 in a factorial design. As pH decreased, shoot and root dry weights increased significantly, while shoot:root ratios remained unchanged. As pH increased, shoot macroelements generally increased, and minor ele- ments decreased. As N-level increased, stem dry weight and shoot:root ratio decreased significantly, while root dry weights did not at higher N-levels. As N-level in- creased, shoot N, Ca and Mn increased, while the levels of other elements remained unchanged. PROPAGATION AND CULTURAL REQUIREMENTS OF PRINSEPIA (PRINSEPIA SINENSIS (OLIV.) OLIV. EX BEAN) BY David James Beattie A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Horticulture 1977 KI tl fc “’0 an- ACKNOWLEDGEMENTS The author wishes to express his sincere appreciation to Dr. Ronald L. Spangler for his guidance and support during the course of this graduate program. Appreciation is also extended to members of the Guidance Committee - Dr. Harold Davidson, Dr. A. L. Kenworthy, Dr. James Kielbaso, and Dr. Dale Linvill - for their suggestions and help during this research. Special gratitude is extended to Dr. Frank Dennis for his encouragement, patience, and helpful suggestions. Gratitude is also extended to Dr. Michael Smith and Ms. Valerie Pearce for their assistance in collection and analysis of data, and to Dr. Kenneth Poff for his time and guidance in spectrophotometric phytochrome analysis. Appreciation is also extended to Hidden Lake Gardens Trust Fund for financial support, without which this program would not have been possible. Final gratitude is extended to my family whose patience and understanding made this graduate program possible. ii L] LI LI 8 Di"? TABLE OF CONTENTS ACKNOWLEDGEMENTS O O I O O O O O O 0 , O O O O O . TABLE OF CONTENTS. . . . . . . . . . . . . . . . . LIST OF TABLES LIST OF FIGURES. . . . . . . . . . . . . . . . . . LITERATURE REVIEW. . . . . . . . . . . . . . . . . SECTION SECTION II: SECTION III: SECTION SUMMARY. I: IV: GERMINATION OF PRINSEPIA (PRINSEPIA SINENSIS (OLIV.) OLIV. EX BEAN): EFFECTS OF STRATIFICATION TIME, GA TREATMENT, TEMPERATURE AND POST GERMINATION CHILLING . . . . . . . . ABSTRACT . . . . . . . . . . . . . . MATERIALS AND METHODS. . . . . . . . RESULTS AND DISCUSSION . . . . . . . LITERATURE CITED . . . . . . . . . . GERMINATION OF PRINSEPIA (PRINSEPIA SINENSIS (OLIV.) OLIV. EX BEAN): INTERACTION OF LIGHT, SEED COAT, AND TEMPERATURE. . . . . . . . . . . . . ABSTRACT . . . . . . . . . . . . . . MATERIALS AND METHODS. . . . . . . . RESULTS AND DISCUSSION . . . . . . . LITERATURE CITED . . . . . . . . . . INFLUENCE OF CHILLED AND NONCHILLED SCIONS AND ROOTSTOCKS IN PRINSEPIA (PRINSEPIA SINENSIS (OLIV.) OLIV. EX BEAN). . . . . . . . . . . . . . . . ABSTRACT o O o o o o o o o o o o o 0 LITERATURE CITED . . . . . . . . . . EFFECT OF PH REGIMES AND N—FERTILIZATION ON GROWTH OF PRINSEPIA (PRINSEPIA SINEN- SIS (OLIV.) OLIV. EX BEAN) . . . . . ABSTRACT . . . . . . . . . . . . . . LITERATURE CITED . . . . . . . . . . LITERATURE CITED . . . . . . . . . . . . . . . . . Page ii iii iv 12 22 24 27 32 48 51 61 62 68 69 72 LIST OF TABLES Table Page SECTION I 1. Effect of stratification at 4 + 2°C treatment on % germination of Prinsepia sinensis seed in soil. One replicate of 25 seeds was used per stratification time . . . . . . . . . . . . . . . 13 2. Effect of germination temp and method of strati- fication on the % germination of Prinsepia sinensis seed. Seeds were stratified at 4 + 2UC for 16 wk, then held at indicated tem for 8 wk . . . . . . . . . 15 3. Effects of germination temp, chilling after ermina— tion, cotyledon removal or chilling at 4 i 2 C on leaf number, shoot length, shoot:root ratio, and growth habit in Prinsepia sinensis. . . . . . . . . . l7 SECTION II 1. Effect of length of exposure to continuous white light given after 24 hr imbibition on the final % germina- tion and germination index after 14 days on Prinsepia sinensis seed removed from endocarp . . . . . . . . . 33 2. Effect of time of exposure to 24 hr light following imbibition on the final % germination and germina- tion index after 14 days on Prinsepia sinensis. . . . 34 SECTION III 1. Effect of inarch and side grafts on scion bud break and shoot growth of Prinsepia sinensis after 6 wk growing in 12 cm pots . . . . . . . . . . . . . . . . 55 2. Effect of inarch grafts on scion bud break and shoot growth of Prinsepia sinensis after 6 wk groWing in 5 cm pots . . . . . . . . . . . . . . . . . . . . . . 56 3. Effect of inarch grafts on scion bud break and growth of Prinsepia sinensis after 6 wk growin in 5 cm pots . . . . . . . . . . . . . . . . . . . . . . 57 SECTION IV 1. Main effects of pH and nitrogen levels on plant dry wt and shoot:root ratio of Prinsepia sinensis . . 65 2. Main effects of nitrogen levels and pH on nutrient levels in shoots of Prinsepia sinensis. . . . . . . . 67 iv Fig LIST OF FIGURES Figure Page SECTION I Effect of cotyledon removal after germination on seedling growth of Prinsepia sinensis after 6 wk, A = 2, B = l, C = 0 cotyledons removed. . . . . . . . 19 Effect of chilling after germination on seedling growth of Prinsepia sinensis after 6 wk. A = 0, B = 7, C = 14, D = 21 days at 4 + 2°C. Note internode elongation. . . . . . T . . . . . . . . . . l9 Scanning electron micrograph of Prinsepia sinensis seedling apices showing leaf primordia (le’de- velopment in nonchilled (top) and chilled (bottom) plants. . . . . . . . . . . . . . . . . . . . . . . . 21 SECTION II Time of exposure to light at different intervals (top) or for different periods of time (bottom) after 24 hours imbibition (I) for Prinsepia sinensis seeds. . . . . . . . . . . . . . . . . . . . 29 Effect of day length on the % germination of Prinsepia sinensis. Light treatments applied during days 1—14 following imbibition. Mean separation by Duncan's multiple range test, 5% level . . . . . . 36 Effect of continuous white light or dark and seed coat removal on the % germination (top) and ger— mination index (bottom) after 14 days on Prinsepia sinensis removed from endocarp. Index based on cumulative no. of seeds germinated on each of days 7, 10 and 14. Bars accompanied by the same letter are not significantly different by Duncan's multiple range test, 5% level . . . . . . . . . . . . 38 Effect of continuous white light or dark and seed coat removal from either the radicle or chalazal end of the seed on the % germination (top) and germination index (bottom) after 14 days on Prinsepia sinensis seed removed from endocarp. Index determined from the cumulative no. of seeds germinated on each of days 4-14. Bars accompanied by the same letter are not significantly different V Figure Page by Duncan's multiple range test, 5% level. . . . . . 41 Effect of continuous white light or dark and temp on the % (top) and-relative rate (bottom) of ger- mination after 14 days on Prinsepia sinensis seed removed from endocarp. Rate determined from the cumulative no. of seeds germinated on each of days 4-14. Data points accompanied by the same letter are not significantly different by Duncan's multiple range test, 5% level . . . , . . . . . . . . . . . . 44 Far-red minus red difference spectrum of etiolated Prinsepia sinensis seedling hypocotyls . . . . . . . 47 SECTION III Effect of grafting nonchilled dwarf-rosetted scions on chilled (left) and nonchilled (right) rootstocks of Prinsepia sinensis. . . . . . . . . . . . . . . . 60 vi Guidance Committee: The journal-article format was adopted for this dissertation in accordance with departmental and university requirements. Sections I and II were prepared and styled for publication in the Journal of the American Society for Horticultural Science while sections IIIand IV were prepared and styled for publication in HortScience. LITERATURE REVIEW Plant history. The genus Prinsepia was named by Royale in the 1830's to honor James Prinsep, an eminent British explorer-traveler. The half dozen or so species of this genera are shrubs, native to the Asiatic main— land, principally eastern China. Prinsepia sinensis (Oliv.) Oliv., often called prin- sepia or cherry prinsepia, is found growing in valley bottoms and along streams in Manchuria and N. Korea, where the climate is similar to that of central Michigan. According to Rehder (5), this hardy shrub (zone 4) has been cultivated since 1896. A mature prinsepia is about 3 meters high, has a dense growth habit, and makes an excellent bar- rier or hedge planting. However, it is mainly valued for its very early bright green foliage, normally appearing somewhat earlier than bush honeysuckle (Lonicera sp.) in East Lansing, Michigan. Masses of creamy yellow flowers (3-5 per node) bloom in April after leaf expansion has started. Numerous bright red, cherry-sized drupe fruits mature in late summer. The fruit is edible, but its tart taste makes it better suited for jellies. Fruit is similar in appearance to cherry, but differs in a number of morphological and anatomical characteristics (2). The bulk of the embryo is cotyledonary tissue surrounded l by a 2-1ayered seed coat or testa, enclosed in a woody, prOminently fissured endocarp. Taxonomists presently classify prinsepia in Rosaceae, but its position within that family is not definite. Some consider it to be a member of the subfamily Prunoideae. However, Sterling (8) recently placed it in a separate subfamily, Prinsepioideae, based on carpellary structure, ovule position, and floral symmetry, all of which differ from those of Prunoideae. Prinsepia's dense growth habit, profuse flowering and edible fruit, lack of insect or disease pests, and early spring growth are desirable characteristics for a landscape shrub. However, prinsepia is seldom used as an ornamental, occurring mostly in arobreta and botanical gardens. Accord- ing to Wyman (ll), prinsepia "is a most serviceable plant and should be grown far more than it is". Prinsepia is not listed in nursery catalogs in Michigan and is probably not available commercially in the United States. Normally, prinsepia seed germinate in late summer and early fall, and seedlings develop a dwarf—rosetted appear— ance. Plants resume normal growth the following spring. Ecologically, such a small slow growing shoot which de- velops a relatively large root system might better survive winter conditions. Dormancy and rest. Plants have many physiological, biochemical and structural mechanisms that permit them to survive under unfavorable environmental conditions. In respone to either an adverse environment, or to genetic mechanisms that predetermine a response, plants enter a state of suspended growth, loosely referred to as dormancy. Literature about dormancy is vast, and the term itself open to many interpretations. Sussman and Havorson (9), who give the broadest possible definition, consider it to be a relative term describing a variety of conditions somewhere between the active vegetative state of growth and that of vitrification. Doorenbos (4) defines dormancy as "any case in which a tissue predisposed to elongate does not do so", whereas Samish (6), includes both quiescence and rest. Quiescence is exogenously controlled, and germination or growth will take place in a favorable environment. Rest, on the other hand, is controlled by endogenous factors such as metabolic blocks and growth inhibitors. During rest, growth or germination or bud growth will not occur even though environmental conditions are favorable. The‘ most common method of overcoming rest is to expose buds, or moist seeds, to temperatures just above freezing for a number of weeks (6). This after-ripening process for seeds is usually referred to as stratification. Seeds that would otherwise germinate may be rendered in- capable of doing so under certain environmental conditions. Germination of fresh, ripe lettuce seed decreases rapidly if temperatures exceed 20°C (10). This condition is referred to as thermodormancy; decreases with time from seed harvest, or may be overcome by exposing the seed to light. Another type of temperature induced dormancy, called secondary dormancy, may be imposed in rose (7) or apple seeds (1) when transferred prematurely to temperatures of 25-300C after part of their stratification requirement has been completed. To overcome secondary dormancy, seeds must be restratified. In all examples found in the literature, temperature induced dormancy always occurs in response to high temperatures, rather than low temperatures. Successful crop production often involves removing or bypassing the resting state in buds or seeds. To do this, plants or seeds must be subjected to special en- vironmental conditions, mainly combinations of light, moisture and temperature. Under these conditions, a number of metabolic events are synchronized, permitting the plant/seed to grow when the environment again becomes favorable. This study was undertaken to investigate and seek methods of overcoming rest in buds and seeds by sub- jecting them to various stratification (cool-moist after- ripening), temperature and light conditions, as well as growth regulators and seed coat removal. In addition, clonal plant response in container culture to various nitrogen levels and media pH was examined. LITERATURE CITED 10. ll. LITERATURE CITED Abbott, D. L. 1955. Temperature and dormancy of apple seeds. Proc. XIV Int. Hort. Cong. 1:746-753. Baranova, A. 1969. Taxonomic studies in the genus prinsepia. Taiwania 11:99-112. Berg, A. R. and T. R. Plumb. 1972. Bud activation for regrowth.‘ In C. McKell, J. Blaisdell, and J. Coodin (ed.) Wildland shrubs - their biology and utilization. USDA For. Serv. Gen. Tech. Rpt. INT-l. Doorenbos, J. 1953. Review of the literature on dormancy in buds of woody plants. Mededel. Land— bouwhogeschool Wageningen 53:1—24. Rehder, A. 1940. Manual of cultivated trees and shrubs. The Macmillan Co., N. Y. Samish, R. M. 1954. Dormancy in woody plants. Annu. Rev. Plant Physiol. 5:183—204. Semeniuk, P. and R. N. Stewart. 1962. Temperature reversal of after-ripening rose seeds. Proc. Amer. Soc. Hort. Sci. 80:615-621. Sterling, F. W. 1963. The affinities of prinsepia. Amer. J. Bot. 50:693—699. Sussman, A. S. and H. O. Halvorson. 1966. Spores: their dormancy and germination. Harper and Row, N. Y. Thompson, R. C. 1936. Some factors associated with dormancy of lettuce seed. Proc. Amer. Soc. Hort. Sci. 33:610-616. Wyman, D. 1971. Wyman's garden encyclopedia. The Macmillan Co., N. Y. SECTION I Germination of Prinsepia (Prinsepia sinensis (Oliv.) Oliv. EX Bean): Effects of Stratification Time, GA Treatment, Temperature and Post Germination Chilling D. J. Beattie and R. L. Spangler Michigan State University East Lansing, MI 48824 Additional index words. Dormancy, scanning electron microscope Abstract. Fresh or dry stored Prinsepia sinensis seeds with intact endocarp germinated satisfactorily, al- though slowly, and chilling of seeds did not promote germination. Prolonged stratification decreased ger- mination. However, if endocarps were removed from seed that had been stratified for 4 and 8 weeks and then had failed to germinate after 8 weeks, germina- tion was completed within 2 weeks when seeds were held in the dark. 6A3 (100 or 500 ppm) hastened germination of seeds in the endocarp but did not increase final germination. Optimum germination temperature was 20°; germination was significantly lower at 150 and was practically nil at 25°C. Regardless of germina- tion temperature, low temperature stratification, or the presence or absence of cotyledons, all seedlings were dwarf-rosetted in growth habit. Normal shoot elongation was restored only when seedlings were chilled. While chilling slightly increased the 6 number of leaves (nodes) per plant, the most noticeable effect of chilling was the marked increase in internode length. Scanning electron microscope examination of apical meristems showed limited development regardless of chilling. The presence of leaf primordia appeared to be of little importance in the resumption of normal shoot elonga- tion. Stratification is required for normal seed germination of many woody perennials. Stratification requirements of many Rosaceous plants have been reported (4,6,7,8,10), but work with Prinsepia sinensis is limited. Wyman (22) obtained immediate germination if seeds were sown soon after fruit ripening in late summer. Fordham (14) found seed germinated well even after 14.5 months of dry storage. One report (1) indicated germination was favored by stratification for 1 month at 40 followed by 2 months at 22°C, which implied prinsepia had a stratification requirement. While prinsepia germinated in response to a cool-warm storage regime (W. G. Ronald, personal communication), germination proceeded slowly over a period of months and seldom exceeded 50%, following such treatment. Some growth promoters increase germination rate, or partially substitute for a stratification requirement. Soaking incompletely stratified Mazzard cherry seeds with intact endocarps in 100 ppm GA for 24 hr partially substituted for the normal stratification requirement (17). Peach seeds soaked in GA solutions for 24 hr after 35 days stratification germinated better than seeds which had not been treated with GA (9). In other studies, however, GA was ineffective on apple seeds (21) and peach seeds (4). Some Rosaceous plants can be induced to germinate without stratification (2, 9, 10). Peach seeds produced plants if the embryo was excised (11). However, such plants usually rosetted, forming abnormally short inter- nodes, and were referred to as physiological dwarfs. Be- cause the shoot failed to elongate normally without chilling, Crocker and Barton (7) suggested this was an example of epi- cotyl dormancy, similar to that found in tree peony. The cause of this dwarfness was considered to be the same as that controlling bud dormancy in a normal plant (3, 12, 13) in that chilling restored normal growth (12, 19). During chilling of peach seeds, the epicotyl underwent considerable expansion and development, including the initiation of new leaf primordia (16). Ledbetter (16) hypothesized young expanding leaves were sources of growth factors responsible for normal internode extension. Methods other than chilling reportedly produced normal seedlings from unstratified seed. Epicotyl dormancy in Viburnum trilobum (15) and Quercus rubra (5) was overcome by removing the cotyledons (15). Cox (15) proposed an in- hibitor diffused from the cotyledons to the meristem, rendering it dormant. Physiological dwarfness in peach was temperature dependent (18). When seeds are germinated at tempera- tures less than 20°C, normal seedlings develop. Pollock's observations agree with von Veh's (20) who obtained normal seedlings from several Rosaceous tree fruits when non- stratified embryos were germinated in 17-180C. Prinsepia seeds germinate out-of—doors in late summer and early fall. However, shoot elongation does not occur until the following spring, although buds expand or may form short internodes. Since little is known about the stratification require- ment of this seed, and preliminary experiments had shown germination to be slow and incomplete, our purpose was to determine how % germination might be increased. In addi- tion, methods were sought to overcome or bypass the dwarf- rosetted stage of seedling development. MATERIALS AND METHODS Seed sources. Ripe Prinsepia sinensis fruit collected on the MSU campus in mid September were crushed and washed to separate the fleshy mesocarp from the woody endocarp. Seeds that floated in water were considered nonviable and discarded. Viable seed was kept moist for 24 hr until used. Additional dry seeds were obtained from Morden, Manitoba, Canada. 10 Stratification requirements. In order to determine the stratification requirement, lots of 25 seeds with endo- carps were soaked in GA3 solutions of 0, 100 and 500 ppm for 36 hr at 20°C, mixed with moist Sphagnum peat moss sealed in plastic bags, and held for o, 4, 8, or 16 weeks at 4 : 2°C. Only one replicate was used per treatment. On removal from the medium, seeds were planted 5 mm deep in soil in 15 x 15 cm plastic trays, which were held under long day conditions. Night temperature was 20°, and occasionally reached 30°C during the day. Plants were watered as need with tap water. Germination was recorded when the hypocotyl hook became visible. Data were recorded weekly for 12 weeks. In a second experiment, dry-stored seeds obtained from Morden, Manitoba, Canada were imbibed in distilled water for 24 hr, then stratified in moist Sphagnum peat moss for 0, 2, 4, or 8 weeks. For each stratification time, 3 repli- cates of 20 seeds each were removed, surface sterilized for 10 min in a 1:10 dilution of NaHClO4 (Clorox), and germi- nated in inverted 100 x 15 mm petri dishes on Whatman #3 filter paper moistened with distilled H20. Petri dishes were floated in a water bath adjusted so the temp at seed height was 20°C under continuous cool white fluorescent light of 8500 ergs cm-zsec—l. Observations were made weekly for 8 weeks, and germination was recorded when the radicle emerged from the endocarp. At the termination of the ex- periment, nongerminated seeds that had been stratified for 4 and 8 weeks were divided into 2 lots, and endocarps were 11 removed from one lot. Seeds, with or without endocarp, were germinated in petri dishes as described above, except the dishes were wrapped in 2 layers of aluminum foil to exclude light. Germination was recorded under dim green light daily for 2 additional weeks. After seeds germinated, seedlings were planted in the greenhouse and maintained under conditions similar to those previously described. In another experiment, the effects on germination of dry storage, stratification medium, and germination temp were determined. Dried seeds were stored in sealed containers at 5 : 2°C. Freshly harvested seeds were stratified in moist Sphagnum peat moss, in vermiculite, or on filter paper. After 16 weeks, dry seeds were vacuum infiltrated with distilled water for 4 hr, and all seeds were germinated in petri dishes as described above. Temp was maintained at 15, 20, or 25°C at seed level. Germina- tion was recorded weekly for 8 weeks. Seeds were considered germinated when the radicle emerged from the endocarp. Epicotyl dormancy. To determine if dwarfing could be prevented by chilling seed immediately after germination, dry-stored seed were removed from the endocarp, imbibed in darkness for 24 hr, and germinated in petri dishes in the dark at 20°C. After 14 days, 110 germinated seeds were stored at 4 : 2°C for 9 days, then planted in 2 cm pots and grown in the greenhouse under long days for 2 months. Another group of seeds was germinated in the same way. Post germination treatments consisted of either cotyledon 12 removal, or chilling for 0, 7, 14, or 21 days at 4 : 2°C. After chilling, 4 replicates of 5 plants each were selected for uniformity, planted in 10 x 15 cm plastic trays, and grown in the greenhouse under long days. After 2 months, shoot length, leaf number, and shoot:root ratios were de- termined. Scanning electron microscope study. Epicotyl develop- ment after chilling was determined by excising meristems from freshly germinated seeds,and seedlings that had been held for 6 weeks at 5 : 2°C. Meristems were placed in 3% glutaraldehyde (in .lM phosphate buffer) for 4 hr, then de- hydrated in an 8-step alcohol series (lo—100%, 20 min each). Samples were critical point dried (DPD Denton DCP-l) using liquid C02, mounted on SEM stubs with Tube Coat (G. C. Elec- tronics, Rockford, 111.), sputter coated with 20-40 nm of gold, and viewed in the SEM (International Scientific In— strument Co. Super Mini III). Accelerating voltage was 15KV. RESULTS AND DISCUSS ION Stratification requirements. Seeds germinated slowly (Table 1), in agreement with data of Ronald (personal com- munication). Unlike his results, germination was maximal for unstratified seed after 12 weeks, and decreased markedly as stratification time increased. GA3 treatment increased germ- ination 2-5 times the control after 6 weeks in the greenhouse but little effect was noted after 12 weeks (Table l). 13 Table 1. Effect of stratification at 4 : 2°C and GA treatment on % germination of Prinsepia sinensis seed in soil. One replicate of 25 seeds was used per stratification time. % germination after: 6 (wk) 12 wk Stratification GA (ppm) GA (ppm) (wk) 0 100 500 0 100 500 0 24 60 56 86 86 96 4 40 - - 72 - - 8 12 20 20 48 72 64 12 4 - — 24 - — 16 0 0 0 16 16 12 14 Germination data after 6 weeks in the greenhouse indicated that the relative effectiveness of GA decreased the longer seeds were stratified. When seeds were stratified for 16 weeks, none germinated after 6 weeks and only 12-16% after 12 weeks. Rotting was not observed in the nongerminated seeds which had been stratified for 16 weeks, then held for 12 weeks in the greenhouse. In a second experiment, stratification of dry seed for 0 or 2 weeks did not affect germination in the light at 20°C, as 73% of both the stratified and nonstratified seeds germinated (data not shown). Seeds stratified for 4 or 8 weeks also failed to germinate after 8 weeks in the light at 20°C. However, when endocarps were removed and seeds placed in the dark for 2 weeks, all seeds without endocarps germ- inated while those with endocarps did not germinate. Thus the endocarp restricts germination in some manner. In testing the effect of germination temp, highest germination occured at 200 regardless of method of strati- fication (Table 2). Forty-six % germinated for all treat- ments at 200 compared to only 24% at 150 and 4% at 25°C. Stratification medium did not significantly affect germ— ination, but dry-stored seed germinated significantly better than did stratified seed, 75% germinating at 20°C. Epicotyl dormancy. Previous studies showed seedlings from stratified or nonstratified seeds, when greenhouse grown, were dwarf-rosetted. Neither cotyledon removal nor low germination temperature were effective in 15 Table 2. Effect of germination temp and method of strati- fication on the % germination of Prinsepia sinensis seed. Seeds were stratified at 4 : 2°C for 16 wk, then held at indicated temp for 8 wk.2 % germination Stratification medium Dry stored Germ temp Filter Vermiculite Peat Mean (0C) paper 15 l7 17 26 36 24 b 20 29 42 38 75 46 c 25 2 4 0 8 4 a Mean 16 m 21 m 21 m 40 n zMean separation within sets by Duncan's multiple range test, 5% level. 16 Preventing rosetting (Table 3, Fig. 1), and cotyledon re- moval reduced seedling vigor as determined by mean shoot length and leaves per plant. Only chilling after germination stimulated seedling shoot growth. Chilling germinated seeds for 14 and 21 days (Table 3) resulted in only 10% dwarfing. Failure of internodes to elongate was responsible for most of the dwarfing. Leaves per plant tended to increase as chilling in creased (Table 3). However, the increase in the number of leaves per plant was modest, relative to the increased shoot: root ratio and shoot elongation ( Table 3 and Fig. 2). Therefore, elongation of internodes was primarily re- sponsible for the increased shoot elongation, rather than increased number of internodes. This agreed with the find- ings of Ledbetter (16), who showed internodes of normal peach seedlings had more and larger pith cells than those of dwarfs. Scanning electron microscope study. Unlike peach (16), in which leaf primordia increased during chilling, prinsepia epicotyls showed little development either before or as a result of chilling (Fig. 3). These experiments indicate prinsepia seeds do not have a stratification requirment. Drying seed does not de- crease germination, but may increase it. A high percentage of seed germinate slowly without stratification. Rapid and complete germination can be obtained within 2 weeks by removing the endocarp and germinating“ seed in the dark at.20°C. l7 .Hm>ma mm .umou mmcmn mamfluase m.cmoczo ma mcEsHoo casuaz coaumummmm cmmzu .mflmhamcm Hmowumflumum Eoum copzaoxw .MHHHMDHOE wmw» owm.a wv.HH to.mm oa am e om onmm.a mow.oa ow.mH 0H ea 0 om nvv.a U0m.oa am.m mm b o om Moo.a an.m now.m 00H 0 o om cmm. cm.m wo.m ooa I a om Amm.av mAm.mV Ao.av ooa I m cm who.a ono.oa nm¢.m ooa I o ma oeumu ucmHm REEL ucmHmI va Ammwcv pm>ofiwu Auov noon Ham mom numcma mucmam coflumcwanmm mGOGOHmuoo mama "poocm mm>mmq uoonm com: MHMBQ Hmumm OOHHHSU MO .02 cofiumcflfinmw cmaaflnococ Scum N .mowmm mmcwapmmm mflmcwcfim mammmcfium cw Danna cusoum 0cm .owumu uoonuuoosm .numcma pecan .HmnEsc mama so 00m H v um mcflaawno Ho Hm>oamu cocoahuoo .cofiumcfifiumm Hmpmm @GHHHHQO .mfimu cowumcflfiumm mo muommmm .m OHQMB 18 Fig. 1. Effect of cotyledon removal after germination on"seedling growth of Prinsepia sinensis after 6 wk. A = 2, B = 1, C = 0 cotyledons removed. Fig. 2. Effect of chilling after germination on seedling growth of Prinsepia sinensis after 8 wk. A = 0, B = 7, C = 14, D = 21 days at 4 + 2 C. Note inter— node elongation. — 19 1 2 Fig. Fig. 20 Fig. 3. Scanning electron micrograph of Prinsepia sinensis apices showing leaf primordia (1p) development in nonchilled (top) and chilled (bottom).plants. 21 10. ll. 12, 10. 11. 12. LITERATURE CITED Anonymous. 1971. Ornamental propagation. Research Branch Rept. Research Station, Morden, Manitoba, Canada. Barton, L. V. 1956. Growth response of physiologic dwarfs of Malus arnoldiana Sarg. to gibberellic acid. Contrib. Boyce Thompson Inst. 18:311—317. Biggs, R. H. 1959. Relation of growth substances to after-ripening of peach seeds. Plant Physiol. 34(supp1): Carlson, R. F. and M. Badizadegan. 1967. Peach seed germination and seedling growth as influenced by several factors. Quart. Bull. Mich. Agr. Exp. Sta. 49:276-282. Cox, L. G. 1942. A physiological study of embryo dor- mancy in the seed of native hardwoods and iris. Ph.D. Thesis, Cornell Univ., Ithaca, New York. Crocker, W. 1948. Growth of plants. Reinhold, New York. and L. V. Barton. 1957. Physiology of seeds. Chron. Bot. Co., Waltham, MA. and . 1931. After-ripening, germination and storage of certain Rosaceous seeds. Contrib. Boyce Thompson Inst. 3:385w404. Donaho, C. W. and D. W. Walker. 1957. Effect of gib- berellic acid on breaking of the rest period in Elberta peach. Science 126:1178-1179. Flemion, F. 1931. After—ripening, germination and vitality of seeds of Sorbus aucuparia L. Contrib. Boyce Thompson Inst. 3:413-439. 1934. Dwarf seedlings from non—after— ripening embryos of peach, apple, and hawthorn. Con- trib. Boyce ThOmpson Inst. 5:205-209. 1959. Effect of temperature, light, and gibberellic acid on stem elongation and leaf develop— ment in physiologically dwarfed seedlings of peach and Rhodotypos.' Contrib. Boyce Thompson Inst. 20:50-57. 22 13° 14. 15. 16. 17. 18. 19. 20. 21. 22. 23 Flemion, F. and E. Waterbury. 1945. Further studies Wlth dwarf seedlings of non-after-ripening peach seeds. Contrib. Boyce Thompson Inst. 13:415-422. Fordham, A. 1962. Methods of treating seeds at the Arnold Arboretum. Proc. Int. Plant Prop. Soc. 12:157-163. Knowles, R. H. and S. Zalik. 1958. Effects of tempera- ture treatment on seed dormancy and of cotyledon removal on epicotyl growth in Viburnum trilobum Marsh. Can. J. Bot. 36(5):561-566. Ledbetter, M. C. 1960. Anatomical and morphological comparisons of normal and physiologically dwarfed seed- lings of Rhodotypos tetrapetala and Prunus persica. Contrib. Boyce Thompson Inst. 20:437-458. Pillay, D. T. N., K. D. Brase, and L. J. Edgerton. 1965. Effects of pretreatments, temperature, and duration of after-ripening on germination of Mazzard and Mahaleb cherry seeds. Proc. Amer. Soc. Hort. Sci. 86:102—107. Pollock, B. M. 1962. Temperature control of physiologi- cal dwarfing in peach seedlings. Plant Physiol. 37:190- 197. Tukey, H. B. and R. F. Carlson. 1945. Morphological changes in peach seedlings following after-ripening treatments of the seeds. Bot. Gaz. 106:431-440. Von Veh, R. 1939. Uber entwicklungsbereitschaft und Wuchsigkeit der embryonen von apfel, pfirsich u.a. Zuchter II:249-255. Walker, D. R. 1970. Growth substances in dormant fruit buds and seeds. HortScience 5:414-417. Wyman, D. 1971. Wyman's garden encyclopedia. The Macmillan Co., New York. SECTION II Germination of Prinsepia (Prinsepia sinensis (Oliv.) Oliv. Ex Bean): Interaction of Light Seed Coat and Temperature D. J. Beattie and R. L. Spangler Michigan State University East Lansing, MI 48824 Additional index words. Phytochrome, photoperiod, secondary dormancy Abstract. Germination of prinsepia seed was inhi- bited by light. The effect was proportional to duration of light exposure after imbibition and decreased as time of exposure was delayed. Photo- reversible phytochrome was detected spectrophoto- metrically in etiolated seedlings, but not in imbibed seeds. Partial removal of the seed coat increased per- cent germination and germination index in light; removal of the chalazal end was more effective than removal of the radicle end. Optimum germina- tion temperature was 20°C in both light and darkness. Holding seeds at 10°C for l to 2 weeks before trans- fer to 20°C markedly reduced germination, while holding at 25°C did not. Since its discovery, phytochrome (5,9,10) has been found to mediate the germination of a number of seeds. Germination of species including Betula pubescens (3), 24 IN”! 25 -g§ulonia_tomentosa (6,30) and Pinus sylvestris (23) are light promoted while others, such as Phacelia tanacetifolia and Amaranthus caudatus (11,19) are light inhibited. How- ever, we know of no references reporting light inhibited germination of woody perennials. Regardless of whether light is promotive or inhibitory, germination is thought to be controlled by the same phytochrome system. The dif- ference occurs when seeds are exposed to white light (18). Light inhibited seeds are more sensitive to the far-red portion of the spectrum, which shifts phytochrome to the physiologically inactive form. Phytochrome must be in the far-red absorbing form to effect germination. This can be brought about by holding seeds to red light (17). Red/ far-red photoreversibility has been demonstrated for both light promoted (5,23) and light inhibited seeds (17,20,21, 22,24,25). Temp greatly modifies the photoperiodic/phytochrome re- sponse of some seeds, while it has little effect on others. Extensive reviews on this subject have been published by Toole (29) and Stokes (27). Black and Wareing (3) found freshly harvested seeds of Betula pubescens germinated only under long days at 15°C, but under either long or short days at 20°C. In Phacelia tanacetifolia, the inhibitory effect of light on germination was only slightly modified by low temp (4,11), while germination of Nemophila insignis seeds were unaffected by day length at high (30°C) temp (4). Schiebe and Lang (26) postulated that high temp may negate 26 the redlight effect on germination of 'Grand Rapids' lettuce by destroying phytochrome. Nyman (23) found the effects of red and far-red irradiation on the germination of Pinus sylvestris to be independent of temp. The role of seed coverings in dormancy of seeds has been investigated, usually with seeds that have a stratifi- cation requirement for normal, rapid germination. Seed coats may inhibit or restrict water uptake (1, 34), oxygen ex- change (31, 32, 34), or leaching of inhibitors (7, 33, 35). In addition, seed coats may restrict normal radicle emerg- ence (12, 13, 14, 15). Evenari and Newman (14) found 'Grand Rapids' lettuce germinated poorly in the dark. However, nearly 100% ger- minated in either light or dark if the seed coat and endo- sperm were removed from the radicle end of the seed. Light inhibited germination of Phacelia tanacetifolia could be overcome by cutting or rupturing the seed coat at the radicle end (12). Cuts at other places, including small holes bored into the seed on either side of the radicle, were ineffective. When the embryonic axis was removed from the seed and cultured, it grew in either light or dark. Thus Chen and Thiman (12) concluded dormancy was due to mechanical restriction by seed coat, and not light. Seeds of Prinsepia sinensis germinate rapidly if removed from the endocarp and held in the dark (2). The :purpose of this study was to investigate the influence of .light, temperature, and seed coat removal on germination. In ad of ph obtai the e surfa (ClorI plast. filte: for ea inaI sourcI Vidlm 27 In addition, seeds and seedlings were examined for evidence of phytochrome. MATERIALS AND METHODS Germination conditions. Prinsepia sinensis seeds obtained from Morden, Manitobe, Canada were removed from the endocarp, imbibed in water in the dark for 24 hr, and surface sterilized for 10 min in a 1:10 dilution of NaHClO4 (Clorox). Seeds were then placed in inverted 100 x 15 mm plastic petri dishes on distilled-water-soaked Whatman #3 filter paper. Three replicates of 10 seeds each were used for each treatment. Petri dishes were floated in water baths in a growth chamber maintained at 20 : 0.5°C. The light source was Sylvania Cool White VHO fluorescent lamps pro— viding 8500 ergs cmC-zsec-1 at seed height. To exclude light in some treatments, petri dishes were wrapped in 2 layers of aluminum foil. Germination was recorded daily for 2 weeks. Dark germinated seeds were counted under dim green light. Seeds were considered germinated when the radicle had emerged 1-2 mm. Germination index was calculated as the cumulative number of seeds germinated on each observation. Analysis of variance was used to determine the statistical significance of observed differences. Effect of time of exposure to light. To test the effect of length of exposure to white light, seeds were exposed to light for 12, 24, or 48 hr after imbibition, the: mine The afte the were Man: cri‘ a c: for for wer to or mix of rat f0] Whe 28 then returned to darkness (Fig. 1). Controls were ger- minated in both continuous light and continuous dark. The effect of a single 24 hr exposure given 1 to 5 days after imbibition was determined. Seeds were maintained in the dark except fOr this one 24 hr period. Control seeds were held both in continuous light and continuous dark. Many seeds are photoperiodic (16), but some have no critical photoperiod (4). To determine if prinsepia had a critical photoperiod, seeds were exposed to white light for periods of 0, 1.25, 2.5, 5.0, 10.0, or 20 hr each day for 14 consecutive days. Two replications of 10 seeds each were used. Seeds from a second seed source were exposed to 0, 1.25, 2.5, and 5.0 hrs of white light each day. Effect of seed coat removal. Seed coats were wholly or partially removed from, or left intact, prior to ger- mination in constant white light or darkness. About 1 mm2 of the seed coat was removed from either the chalazal or radicle end of the seed. Effect of germination temp. Optimum germination temp for seeds with intact endocarp was 20°C (2). To determine whether light modified the response to temp, seeds were removed from the endocarp and germinated at 15°, 20° or 25°C. Induction of secondary dormancy. Many seeds, including lettuce, enter a state of secondary dormancy when exposed to high temp (28). Long periods of stratification may in- duce secondary dormancy in prinsepia seed (2). To determine ‘whether this was an instance of secondary dormancy, seeds 29 Fig. 1. Time of exposure to light at different intervals (top) or for different periods of time (bottom) after 24 hours imbibition (I) for Prinsepia sinensis seed. 30 OQIO '«IO .2. NpIo h20.4 #800 ¥¢4.(O Odu Odo O.m m.“ mué b .on .ov a a 36 .om ...\._.. NOILVNIHUSS X 37 of light. On repeating the experiment, parallel data were obtained for 0. 1.25, 2.5, and 5 hr; however, differences were not statistically significant. Effect of seed coat removal. The presence of a seed coat inhibited % germiantion in light but not in dark, while seed coat removal improved the index of germination in both light and dark (Fig. 3.) Light x seed coat in— teraction was significant at 1%. Light, independent of seed coat removal, inhibited while dark promoted germina— tion. Light was more inhibitory in the presence of a seed coat, although germination index was promoted by seed coat removal in the dark. Removal of the seed coat at the chalazal or radicle end of the seed increased % germination and germination index in the light, but had less effect in the dark (Fig. 4.) Light x seed coat removal was signifi- cant at the 1% level so that dark, independent of seed coat removal, promoted germination while light inhibited germ- ination. Chalazal end seed coat removal resulted in sig- nificantly higher % germination and germination index than did radicle end removal or intact seed coats. It is not known if prinsepia seed coats inhibit norm- al water uptake and expansion of the embryo as in lettuce seed (14), but it is suggested by the promotive effect of partial seed coat removal, especially dark germinated seeds ( Fig. 4.). There was little promotive effect where seed coat was removed at the radicle end and light germinated while chalazal end removal resulted in good germination percentage in either light or dark. Fig. 3. Effect of continuous white light or dark and seed coat removal on the % germination (top) and germination index (bottom) after 14 days on Prinsepia sinensis removed from endocarp. Index based on sum of cumulative no. of seeds germinated on each of days 7, 10 and 14. Bars accompanied by the same letter are not significantly different by Duncan's multiple range test, 5% level X GERMINATION INDEX GERMINATION 100 50 30 39 SEED COAT: - INTACT - "noun DARK LIGHT SEED COAT: INTACT REMOVED DARK LIGHT Fig. 3 Fig. 4. Effect of continuous white light or dark and seed coat removal from either the radicle or chalazal end of the seed on the % germination (top) and germination index (bottom) after 14 days on Prinsepia sinensis seed removed from endocarp. Index determined from the cumulative no. of seeds germinated on each of days 4-14. Bars accompanied by the same letter are not significantly different by Duncan's multiple range test, 5% level. 41 100 \V .mnc: E \ .IuoIcu .— < E 50 I ‘-~ E a \ mcmuzu 0 8 O 0 ttttt 100 GERMINATION INDEX 50- E mncr - RADICLE Fig. 4 42 Effect of germination temp. In either light or dark, 0 and 200 and dropped % germination increased between 15 markedly at 250C (Fig. 5 ). Index was also increased in the dark between 150 and 20°, dropping markedly at 25°C, but there was no difference in index amoung germination temp in the light. A light x temp interaction was significant at 1%. Index and % germination were dark promoted and light inhibited. Optimum germination temp of 200 C ag— reed with the results reported earlier for seeds with in- tact endocarps (2). Unlike the findings of Black and Wareing (3), and Schiebe and Lang (26), temp did not com- pletely obviate the light effect on germination % but did so for germination index. Induction of secondary dormancy. Ten % of seeds held in the dark for 2 weeks at 250 germinated, while none of those held at 10°C germinated ( data not shown ). When 0 nongerminated seeds were transferred to 20 for 1 week, 100 % of the seeds previously held at 250 vs. only 37% of those held at 100C germinated. On transfer to 20°, germination after 1 week was 96% and 4% for seeds previously held at O 25 and 100C, respectively. At both 250 and 100C, seeds were obviously thermodormant. Dormancy appears to be transitory for the 250 seeds as they germinate readily when returned to 200C. However, 0 dormancy in the 10 C seeds is much deeper. These results Fig. 5. Effect of continuous white light or dark and temp on the % germination (top) and germina- tion index (bottom) after 14 days on Prinsepia sinensis seed removed from endocarp. Index was determined from the cumulative no. of seeds germinated on each of days 4-14. Data points accompanied by the same letter are not signif- icantly different by Duncan's multiple range test, 5% level. 10¢) 44 z ‘3 I—- DARK p ; DI-D LJGHT i 50 c In 0 no i D U a C - . riiiJfl:-- 15 2O 25 TEMPERATURE I°ct 100 x In a o z u : fiaflTI°°°’ ,2 so < I-Il DARK 2 ; DIID LIGHT I: In G m U [110/ \Im - n q 15 2O 25 TEMPERATURE I°CI Fig. 5 45 may, in part, explain why germination of prinsepia seeds in the endocarp declined as stratification was prolonged (2) . Phytochrome. Photoreversible phytochrome was detected repeatedly in etiolated seedlings. Fig. 6 is a sample difference spectrum illustrating photoreversibility. How- ever, attempts to detect phytochrome in imbibed cells were unsuccessful . Fig. 6. 46 Far-red minus red difference spectrum of etiolated Prinsepia sinensis seedling hypocotyls. A o .005 .000 - .005 - .010 47 600 700 000 WAVELEHGT H (mu) Fig. 6 10o LITERATURE CITED Barton, L. V. 1965. Dormancy in seeds imposed by the seed coats. Encycl. Plant Physiol. 15(2):727-745. I3eattie, D. J. and R. L. Spangler. 1977. Germination sstudies in Prinsepia (Prinsepia sinensis (Oliv.) Oliv. 13X Bean): Effects of stratification time, GA treatment 'temperature and post germination chilling. J. Amer. Soc. Hort. Sci. (in preparation). Black, M. and P. F. Wareing. 1955. Growth studies in woody species. VII. Photoperiodic control of germina- tion in Betula pubescens Ehrh. Plant Physiol. 8:300-316. and . 1960. Photoperiodism in the light inhiblted seed of Nemophila insignis. J. Expt. Bot. 11:28-29. Borthwick, H. A., S. B. Hendricks, M. W. Parker, E. H. Toole, and V. K. Toole. 1952. A reversible photo- reaction controlling seed germination. Proc. Nat. Aca. SCi., U. S. 38:662—666. and E. H. Toole. 1965. Phytochrome control of Paulonia seed germination. Israel J. Bot. 13:122—123. Bradbeer, J. W. 1968. Studies in seed dormancy. IV. The role of endogenous inhibitors and gibberellin in the dormancy and germination of Corylus avellana seeds. Planta 78:266-276. Butler, W. L. and D. W. Hopkins. 1970. Higher deriva- tive analysis of complex absorption spectra. Photochem. Photobiol. 12:439-450. , S. B. Hendricks, and H. W. Siegelman. 1960. ‘ In V1VO and in vitro properties of phytochrome. Plant Physiol. 35(Supp.):xxxii. , K. H. Norris, H. W. Siegelman, and S. B. HendricEs. I959. Detection, assay, and preliminary purification of the pigment controlling photoresponsive development of plants. Proc. Nat. Acad. Sci., U. S. 45:1703—1708. 48 ll. 12. 13. 14. 15. 23. 24, 49 Chen, S. S. C. and K. V. Thimann. 1964. Studies on tile: germination of light—inhibited seed of Phacelia tanacetifolia. Israel J. Bot. 13:57-73. and . 1966. Nature of seed ciormancy in Phacelia tanacetifolia. Science 153:1537-1538 If—‘u‘sashi, Y. and A. C. Leopold. 1968. Physical forces 2L1) dormancy and germination in Xanthium seeds. Plant IPIIysiol. 43:871—876. livenari, M. and G. Neuman. 1952. The germination of let- truce seed. II. The influence of fruit coat, seed coat, 61nd endospern upon germination. Bull. Res. Counc. Israel 2:75-78. Ikuma, H. and K. V. Thimann. 1963. The role of seed coats in germination of photosensitive lettuce seeds. Plant Cell Physiol. 4:169-185. Isikawa, S. 1954. Light sensitivity against germination. I. Photoperiodism of seeds. Bot. Mag., Tokyo 67:51-56. Jones, M. B. and L. F. Bailey. 1956. Light effects on the germination of henbit (Lamium amplexicaule L.) Plant Physiol. 31:347-349. Kendrick, R. E. 1976. Photocontrol of seed germination. Science Progress 63:347—367. and B. Frankland. 1968. Kinetics of phytochrome decay in Amaranthus seedlings. Planta 82:317-320. and . 1969. Photocontrol of germination in Amaranthus caudatus. Planta 85:326— 339. , C. J. P. Spruit, and B. Frankland. 1969. Phytochrome in seeds of Amaranthus caudatus. Planta 88:293—302. ManCinelli, A. L., 1966. Phytochrome Bot. Gaz. 127:1—5. H. A. Borthwick, and S. B. Hendricks. action in tomato-seed germination. Nyman, B. 1963. Studies on the germination in seeds of Scots pine (Pinus sylvestris L.) with special reference to the light factor. Studla Forestalia Suecica No. 2 Skogshogskolan, Stockholm. pp. 1—64. Rollin, P. 1964. Phytochrome control of seed germina- tion. pp. 230—254. In K. Mitrakos and W. Shropshire, Jr. (eds.) Phytochrome. Academic Press, N. Y. 25. 26. 27. 28. 29. 50 RK>1£Lin, P. R. Malcoste, and D. Eude. 1970. Le role du phytochrome dans la germination des graines de IQGEHuophila insignis L. Planta 91:227-234. Schiebe, J. and A. Lang. 1969. Lettuce seed germina- tlixbn: Effects of high temperature and of repeated IEaar-red treatment in relation to phytochrome. Photo— <:11em. Photobiol. 9:143-150. SStokes, P. 1965. Temperature and seed dormancy. Ifincycl. Plant Physiol. 15(2):746-803. frhompson, R. C. 1936. Some factors associated with (dormancy of lettuce seed. Proc. Amer. Soc. Hort. Sci. 33:610-616. Toole, V. K. 1973. Effects of light, temperature and their interactions on the germination of seeds. Seed Sci. Tech. 1:339—396. Toole, E. H., V. K. Toole. H. A. Borthwick, S. B. Hen- dricks, and R. J. Downs. 1958. Action of light on germination of seeds of Paulonia tomentosa. Plant Physiol. 33(Supp.):xxiii. Visser, T. 1954. After-ripening and germination of apple seeds in relation to the seed coats. Proc. Kon. Ned. Akad. Wetenschap, Ser.C. 57:175-185. . 1956. The role of seed coats and tempera- ture in after-ripening, germination, and respiration of apple seeds. Proc. Kon. Ned. Akad. Wetenschap, Ser.C. 59:211-222. Wareing, P. F. and H. A. Foda. 1957. Growth inhibitors and dormancy in Xanthium seed. Physiol. Plant. 10:266- 280. Webb, D. P. and E. B. Dumbroff. 1969. Factors in— fluencing the stratification process in seeds of Acer saccharum. Can. J. Bot. 47:1555—k563. and P. F. Wareing. 1972. Acer pseudoplatanoides: Seed dormancy in The role of covering structures. Infl influence of Chilled and Nonchilled Scions and Rootstocks translocatable stimulii involved in bud dormancy. West- wood and Chestnut (5) made reciprocal grafts of pear species having long (Pyrgs communis 'Bartlett') vs. short (Pyrus calleryana) chill requirements to determine the respective effects of scion vs. rootstock on bud dormancy. 'Bartlett' scions grafted to P. calleryana rootstocks required fewer chilling hours for growth than did nongrafted 'Bartlett'. Grafting actively growing P. calleryana scions on the same on Bud Dormancy in Prinsepia (Prinsepia sinensis (Oliv.) Oliv. EX Bean) D. J. Beattie and R. L. Spangler Michigan State University East Lansing, MI 48824 Additional index words. Chilling Abstract. Buds of nonchilled scions of Prinsepia sinensis were induced to grow when grafted on chilled rootstocks, and growth of chilled buds was depressed by grafting on nonchilled rootstocks. Nonchilled dwarf-rosetted scions grew when grafted on nonchilled rootstocks, but failed to grow when grafted on nonchilled rootstocks. These results suggest either the presence of a graft translocated stimulus, or lack of an in— hibitor, of root origin that effects bud break. Grafting experiments are used to examine the role of 51 bra: qrc tie it 52 pfanch with partially chilled 'Bartlett' buds stimulated ngWth of the latter, while growth of 'Bartlett' buds depressed by grafting onto partially chilled rootstocks. For these results, the authors hypothesized the presence of a translocatable stimulus involved in rest. Chandler (l) grafted chilled apple scions onto chilled and nonchilled rootstocks. Growth was normal on chilled, but poor on non- chilled rootstocks. Nienstaedt (3) side grafted nonchilled white spruce scions onto chilled and nonchilled Norway and white spruce rootstocks. After one season, scions had grown slightly more on chilled than on nonchilled rootstocks. Nesterov (4) observed little shoot growth when nonchilled apple and plum scions were grafted onto young chilled trees of the same species. However, nonchilled scions grew vigorously when grafted onto older stumps, which would sug- gest either a root system volume or age effect. Chilled scions grew poorly when grafted onto dormant rootstocks. Excised peach embryos germinated without chilling, but seedlings remained dwarf. Flemion (2) could not induce normal growth by grafting these seedlings on actively growing normal seedlings and concluded that the site of this type of dormancy was in the shoot. Prinsepia stops growing in June at a time when many other plants are still actively growing. Preliminary ex- periments showed shoot tip removal, extended photoperiod, ‘or heat treatment had little effect on inducing bud break once terminal growth had ceased. The purpose of this study 53 493 t0 determine if bud dormancy could be influenced vi grafting. All grafts were made with plants of a single clone except dwarf-rosetted plants propagated from seed. Plants were potted in either 5 or 12 cm pots. Prior to grafting, chilled plants were held at 4 : 20C for 1500 hr. During this time, all leaves abscissed. Unchilled plants were considered in the initial stages of rest. Plants had been maintained under long-days (interrupted nights) in a greenhouse and had ceased growth 4 months prior to grafting. Side grafts were prepared by inserting a 3-bud scion (taken from the median 1/3 of the donor plant) into the lower 1/3 of the rootstock stem. Excess rootstock was removed 1 cm above the graft. For inarching grafts, the rootstock and scion plants were removed from pots and approach grafted on the lower 1/3 of their stems. The inarched graft com- bination was replanted in a single pot. All grafts were wrapped with grafting rubbers, and plants were shaded and misted as necessary until grafts had knitted. Nonchilled check plants were cut back to 1/3 their original size and defoliated. Following chilling, chilled stock plants were cut back to 3 buds immediately above soil level. Plants were maintained under long days ( nights interrupted with 4 hr incandescent light) with night temp of 200 and day- time temp of 200 to 300C. When nonchilled rootstock (whole) plants were pruned and defoliated, they grew very little, whereas buds of IlOllt 1’00 V81 54 67n£fliilled scions grew vigorously When grafted on chilled 1Coot-Stocks (Table l) . However, when buds of chilled scions were side grafted on a nonchilled rootstock, some buds broke and grew, but shoot growth was only 15% of that on the chilled rootstock plant. Inarching of nonchilled rootstock plants to chilled scion plants similarly de- pressed scion bud growth. Similar results occured with smaller plants grown in 5 cm pots (Tables 2 & 3). Buds failed to grow on non- chilled rootstock plants (Table 2), whereas inarching chill- ed scion plants to chilled rootstock plants induced growth similar to that of chilled (ungrafted) rootstock plants. Grafting together 2 chilled plants stimulated growth (Table 2), probable due to the presence of 2 root systems. A small- er increase was noted when these treatments were repeated (Table 3). Also, when a nonchilled rootstock was inarched into a chilled scion plant, shoot growth was depressed about 50%, considerable more than the 20% depression noted in Table 2. When chilled rootstock plants were inarched onto nonchilled scion plants, buds broke, but growth was only 15 % that of the chilled rootstock and little more than the nonchilled rootstock. The reason for this is unclear, esp— ecially when bud break and vigorous growth occured in this same graft combinatoin in Tables 1 & 2. When scions from nonchilled, dwarf—rosetted seedlings were grafted on chilled and nonchilled rootstocks, an avg of 2.5 nonchilled scion buds per plant grew an avg 256 mm in .meMHHomwp can pquumw NH om I m pmaaflnococ\pwaafi£ocoz we we I ma pwaafinococ\cwaawcu mma we I om Umaafl£o\pmaawcocoz ewummhm deem HNH em I OH cwHHH£O\pmHHH£ocoz mmm em I oH U0HHH£UE0E\U¢HHM£O pmuwwum noumcH ma v ma I xoouwuoou cmaaflsocoz «AN mm OH I xooumuOOh emaaeao NmecmHm wHOSB .EEV can coflom Awe Mucus mascam mummum Ham nn3oum m>< U59 Gofiom mo oz xooumpoou\c0Hom Mo 6? .meom EU NH ca mcfi3oum #3 w umumm mfimcwcfim mammmcflum 30Hw Doonm new xmmun can EOHOm co mummym mean can nuance mo powmmm .H manna .UwumfiHOwa can vacuums mm he I m pmHHHQO\©mHHfl£U mm mm I m Umaafiso\cmaafinocoz pmummum nonmcH o 0 ma I mxooumuoou cmaaflnocoz em om ma I mxooumuoou cmaafico Nmunmam mHOQB .88. can coeom Aw. xcwun wucwam mummum “mm £u3oum m>¢ U59 cofiom mo 02 xooumuoou\c0fiom .mpom 80 m EH mcfl3oum #3 m kumm mflmcmcflm memmmcwnm MO np3onm poonm cam xmmun can coflom co mummnm noumcfl mo powwmm .N magma .waMHHOMmp paw emcsumn ma mm ma I cmaaenococ\wmaaflcocoz we mm me I emafiezoxemaaeeoeoz mm mm ma I COHHHSOGOG\UOHHASU NMH Hm ma I pmHHHQO\UmHHH£U pwummuw noumcH MH em I ma snowmpoou emeeeeoeoz mma em I ma xooumeooh ewafieeo Nmucmam oaonz .88. can :oflom .wv xmwnn mucmHm mummum Mom £u3onm m>¢ can coflom mo oz Mooumhoon\coflom .muom Eu m ca mGABOHm M3 w chwm wflmcwcflm MA mmcaum mo npzoum pcm xmwhh pan coHom co mummum mousse mo uommwm .m magma 58 j’ength, whereas only .5 of the nonchilled scion buds grew less than 2 mm (Fig. 1). While graft results with prinsepia are not complete, they appear to support Westwood and Chestnut's (5) hypothesis that a graft translocated stimulus of root origin is in- volved in breaking dormancy, and does not support Flemion's (2) belief that the site of dormancy is in the shoot, es- h] pecially for dwarf-rosetted seedlings. Fig. 1. Effect of grafing nonchilled dwarf-rosetted scions on chilled (left) and nonchilled (right) rootstocks or Prinsepia sinensis LITERATURE CITED Chandler, W. H. 1960. Some studies of rest in apple trees. Proc. Amer. Soc. Hort. Sci. 76:1—10. Flemion, F. and E. Waterbury. 1945. Further studies with dwarf seedlings of non-after—ripening peach seeds. Contrib. Boyce Thomp. Inst. 13:415-422. Nienstaedt, H. 1959. The effect of rootstock activity on the success of fall grafting of spruce. J. For. 57:828-832. Nesterov, J. S. 1956. Dormancy in fruit trees. Hort. Abst. 27(1):109. Westwood, M. N. and N. E. Chestnut. 1964. Rest period chilling requirement of Bartlett pear as related to Pyrus calleryana and P. communis rootstocks. Proc. Amer. Soc. Hort. Sci. 84:82-86. 61 IIIIIIIII Effect of pH Regimes and N-fertilization on Growth of Prinsepia (Prinsepia sinensis (Oliv.) Oliv. EX Bean) D. J. Beattie and R. L. Spangler Michigan State University East Lansing, MI #48824 Additional index words. Mineral nutrition, dry weight Abstract. Container grown plants of Prinsepia sinensis were supplied with 4 levels of nitrogen at media pH of 4, 6, and 8 in a factorial design. As pH decreased, shoot and root dry weights increased significantly, while shoot:root ratio remained unchanged. As pH increased, shoot macroelements generally increased, and minor elements decreased. As N-level increased, stem dry weights did not at higher N-levels. As N- level increased, shoot N, Ca and Mn increased, while the levels of other elements remained unchanged. Some unusual ornamental plant materials are seldom used for a lack of information about their culture. ‘Prinsepia sinensis, commonly called prinsepia, is a good example. A mature prinsepia is about 3 m high with thorny twigs and a dense growth habit, making it a valuable hedge or barrier plant. Prinsepia is one of the first plants to leaf out in the spring and is quickly covered with masses of yellowish 62 63 flowers. Numerous edible cherry-sized fruits mature in late summer and are eaten by a variety of wildlife. Prinsepia is native to North Korea and Manchuria and is reliably hardy as far north as Morden, Manitoba, Canada. Although it has been cultivated since the late 1800's, little information is currently available about its cul- ture and, in particular, nutrient requirements. One method of establishing general guidelines for crops about which little is known is to grow them in containers (2). Production of woody ornamentals in containers is becoming an increasingly popular nursery practice. Ad- vantages include the relative ease with which media pH can be adjusted and nutrient levels controlled. A pre— liminary study in 1975 indicated that prinsepia responded to high nitrogen fertilization. Since soil or media pH largely determines efficiency of nutrient uptake, an experiment was designed to determine the effect of both pH and N-fertilization on growth of Prinsepia sinensis. Well-rooted clonal cuttings of prinsepia were planted in 1 liter plastic nursery containers containing a steam- pasteurized medium consisting of equal vol of Sphagnum peat moss, horticultural grade perlite and sandy loam to which was added triple superphosphate (45% P205) at the rate of 1.7 kg/m3. Treatments consisted of a factorial combination of 4 conc of N and 3 media pH levels. Four replicates of 7 uniform plants each were arranged in a randomized block de- sign. Media pH levels were 4, 6 and 8. Based on $011 64 titrations, pH (6 initially) was adjusted to 4 by addition of concd H2804, and to pH 8 by adding CaO. At each fertilization, 375 ppm K was supplied as fertilizer grade KCl, and 0, 400, 800, or 1200 ppm N as fertilizer grade NH4NO3. Solutions (150 ml per container) were applied weekly from May 20 to September 9, 1976. Be- tween fertilizations, containers were watered daily with 125 ml of water supplied by a modified microtube irrigation system. At harvest, a soil sample was taken from each pot, mixed, and final media pH was measured. Tops were separated from roots and each was dried in a forced draft oven. After recording dry wt, samples were ground in a Wiley Mill to pass a 40 mesh sieve, and analyzed for macro and minor ele- ments. N was determined by Macro-Kjeldahl (l), K by flame spectrophotometry (Beckman model B), and other elements on a spark emission spectrograph (Applied Research Laboratories Quantograph (3) ). Final media pH ranged from 7.8 to 8.1, presumably due to the irrigation water which had a pH of 8.1. A greater range in final pH was found in response to N-fertilization, varying from 7.6 at 1200 ppm N to 8.2 for 0 N. These data reflect, in part, the acid reaction produced by nitrifica- tion of the ammonium ion in NH4NO3. Max dry wt production occurred with initial pH of 4 and 1200 ppm N. Shoot and root dry wt was halved as pH in- creased from 4 to 8 (Table 1). Shoot wt doubled as N levels increased from 0 to 1200 ppm, but root dry wt did not increase 64 titrations, pH (6 initially) was adjusted to 4 by addition of concd H2804, and to pH 8 by adding CaO. At each fertilization, 375 ppm K was supplied as fertilizer grade KCl, and 0, 400, 800, or 1200 ppm N as fertilizer grade NH4NO3. Solutions (150 ml per container) were applied weekly from May 20 to September 9, 1976. Be— tween fertilizations, containers were watered daily with 125 ml of water supplied by a modified microtube irrigation system. At harvest, a soil sample was taken from each pot, mixed, and final media pH was measured. Tops were separated from roots and each was dried in a forced draft oven. After recording dry wt, samples were ground in a Wiley Mill to pass a 40 mesh sieve, and analyzed for macro and minor ele- ments. N was determined by Macro-Kjeldahl (l), K by flame spectrophotometry (Beckman model B), and other elements on a spark emission spectrograph (Applied Research Laboratories Quantograph (3) ). Final media pH ranged from 7.8 to 8.1, presumably due to the irrigation water which had a pH of 8.1. A greater range in final pH was found in response to N-fertilization, varying from 7.6 at 1200 ppm N to 8.2 for 0 N. These data reflect, in part, the acid reaction produced by nitrifica- tion of the ammonium ion in NH4NO3. Max dry wt production occurred with initial pH of 4 and 1200 ppm N. Shoot and root dry wt was halved as pH in- creased from 4 to 8 (Table 1). Shoot wt doubled as N levels increased from 0 to 1200 ppm, but root dry wt did not increase 65 Table 1. Main effects of pH and N levels on dry wt and shoot:root ratio of Prinsepia sinensis plants.z Treatment Final Dry wt per plant (9) shoot:root pH ratio Shoot Root pH 4 7.8 14.8c 22.3c 0.63a 6 8.0 10.1b 15.7b 0.63a 8 8.1 6.6a 11.0a 0.58a N (ppm) Y 0 4.79a 12.4a 0.51a 400 6.72b 16.8b 0.61b 800 7.35b 18.3b 0.64bc 1200 7.70 17.8b 0.70c zMean separation within columns and sets by Duncan's multiple range test, 5% level. Interaction was not significant at the 5% level. ySupplied as NH4NO3 66 Significantly above the 400 ppm fertilizer level. shoot:root ratio also increased. As might be expected, plant N increased as N levels increased (Table 2), apparently the rate of N uptake was not saturated at the highest N levels. Although the max level of N used in this study (1200 ppm) may be considered extremely high, plants were able to utilize it. However, the ammonium may not have been used at all, re- sponse being due primarily to the presence of nitrate. Plant K and P uptake did not increase above the 400 ppm N level. As soil pH increases, major nutrients like N, P, K, Ca, and Mg generally become more available, while minor elements become less available (4). In this ex- periment, plant N and Ca increased with pH, K and Mg increased slightly, and P remained relatively unchanged. Fe deficiency is often associated with increased pH (4), but in prinsepia, plant Fe actually increased with pH. Mn decreased while the level of other minor elements remained stable. From this study, we conclude that container grown prinsepia grew best at a relatively low pH with a high supply of N. Because media pH was not controlled after the initial adjustment, maximum growth may not have been attained. Additional work will be required to establish the optimum pH. 67 .Hm>wH .1: NANBMID.»:4I .m e 02 mz mm wweammnm z.n .Hm>wH mm on» us undueMflcmHm no: mm3 coauomnwch mm .hmwu wmcmn meHuHDE m.cmocsn hp mumm 0cm mcfidaoo cenuez GOeDMHmmmm cmwzn home em.mm mm.mm am.m heem ooeh hmm. um~.H hoe. hoe. emm.m oome home we.em we.om em.m hemem hmee hem. ohoe.e hoo. heo. omo.m oom memh mh.mm wo.om me.m meem mom hem. hmH.H emo. hoe. hme.e ooe mmhm me.mm me.om me.m hemom wee eem. mom.o hoe. moo. weh.e o Arielle comm hm.mm mm.mm mm.m comm emm hem. ohm.e hoe. hoe. hom.e m emom hmo.mm mm.om me.m heom mem hom. heo.H woo. woo. hhom.e o meme mm.mm we.mm ee.m wemm hoeh emm. meo.e hoe. emo. eme.H e Ame Awe Hm hm m so we as o: mo m M z hemshmmue N.mflwcmcem mflmmmneum mo mucosm CH mH0>mH unweupsc so cmmoupeq cam mm Mo whommmw CHM: .N OHQMB LITERATURE CITED Anonymous. 1970. Methods of analysis of the association of official agricultural chemists. Eleventh ed. Washington, D. C. Baker, K. (ed). 1957. The U. C. system. Calif. Agr. Expt. Sta. Ext. Serv. Manual 23. Carpenter, P. N. 1964. Spectrographic analysis of plant tissues. Maine Agr. Expt. Sta. Misc. Publ. 666. Tisdale, 5. L. and W. L. Nelson. 1975. Soil fer- tility and fertilizers. The Macmillan Co., N. Y. 68 L J #3 SUMMARY Botanical gardens and arboreta abound with plants that are seldom used, but have potential landscape value. For example, Prinsepia sinensis has been known in culti— vation since the late 1800's but has never "caught on". However, research in this laboratory has clarified some of the conflicting and incomplete reports about its propa- gation and culture. Fresh or dry-stored prinsepia seeds with intact endo— carps germinate satisfactorily although slowly. Prolonged stratification sharply reduced germination. Presence of an endocarp may have been in part responsible for this. Seeds with intact endocarps stratified for 4 and 8 weeks that did not germinate after 8 weeks, did so within 2 weeks when then removed removed from the endocarp and germinated in the dark. Soaking in GA solutions (100 and 500 ppm) hastened germination of seeds in the endocarp, but did not affect final germination %. Optimum germination temp for seeds with or without endocarp was 20°; decreased signi- ficantly at 15° and practically nil at 25°C. Holding seeds at 10° for 1—2 weeks before transfer to 20° markedly reduced germination, while holding seeds at 25°C did not. When re- moved from the endocarp, seed germination is inhibited by 69 70 light. Partial seed coat removal increased germination in the light, removal at the chalazal end being more effective than at the radicle end. Light inhibition of intact seeds removed from the endocarp was proportional to the duration of exposure and decreased as the time of exposure was de- layed. Photoreversible phytochrome was detected spectro— photometrically in etiolated seedlings but not in imbibed seeds. Seeds from chilled or nonchilled seeds were dwarf- rosetted in growth habit. Normal shoot elongation occured u only when seedlings were chilled. The most noticable effect of chilling was on internode elongation. Scanning electron microscope examination of seedlings showed no significant change in apical morphology as a result of chilling. While some of the basic environmental factors affect prinsepia seed germination, more work is needed to obtain more rapid germination from seeds with intact endocarps. In addition, further studies should examine whether light affects germination of seeds with intact endocarps, as well as to establish the physiological basis for the anomolous low—temp induced secondary dormancy. Prinsepia stops growing early in June when other plant are still actively growing. Once growth has ceased, extend- ed photoperiod, heat treatment, or removing the shoot tip has little or no effect on bud break. However, nonchill— ed buds were induced to grow when grafted onto chilled rootstocks. Further grafting experiments are needed to 71 clairfy the relative influence of the stock and scion on bud growth. Container grown prinsepia grows best at relatively low media pH and with a high level of nitrogen. pH values rose dramatically, probably due to high pH of the water used for irrigation. Since media pH was not regulated after initial adjustment, further work will be required to establish pH values as well as levels of other macro and micronutrients. 10. ll. 12. LITERATURE CITED Abbott, D.L. 1955. Temperature and dormancy of apple seeds. Proc. XIV Int. Hort. Cong. 1:746—753. Anonymous. 1970. Methods of analysis of the official agricultural chemists. Eleventh ed. Washington D. C. . 1972. Ornamental propagation. Research Branch Rept. Research Station, Morden, Manitoba, Canada. Baker, K. (ed). 1957. The U. C. System. Calif. Agr. Exp. Sta. Ext. Serv. Manual 23. Baranova, A. 1969. Taxonomic studies in the genus prinsepia. Taiwania 11:99—112. Barton, L. V. 1956. Growth response of physiologic dwarfs of Malus arnoldiana Sarg. to gibberellic acid. Contrib. Boyce Thompson Inst. 18:311-317. . 1965. Dormancy in seeds imposed by the seed coats. Encycl. Plant Physiol. 15(2):727—745. Beattie, D. J. and R. L. Spangler. 1977. Germination of Prinsepia (Prinsepia sinensis (Oliv.) Oliv. EX Bean): Effects of stratification time, GA treatment, tempera- ture and post germination chilling. J. Amer. Soc. Hort. Sci. (in preparation). Berg, A. R. and T. R. Plumb. 1972. Bud activation for regrowth. InMcKell, J. Blaisdell, and J. Coodin (ed.) Wildland shrubs — their biology and utilization. USDA For. Ser. Gen. Tech. Rpt. INT—l. Biggs, R. H. 1959. Relation of growth substances to after-ripening of peach seeds. 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'Proc. Kon. Ned. Akad. Wetenschap, Ser.C. 59:211-222. Von Veh, R. 1939. Uber entwicklungsbereitschaft und Wuchsigkeit der embryonen von apfel, pfirsich u.a. Zuchter 11:249-255. Walker, D. R. 1970. Growth substances in dormant fruit buds and seeds. HortScience 5:414-417. Wareing, P. F. and H. A. Foda. 1957. Growth inhibitors and dormancy in Xanthium seed. Physiol. Plant. 10: 266-280. Webb, D. P. and E. B. Dumbroff. 1969. Factors influ- encing the stratification process in seeds of Acer saccharum. Can. J. Bot. 47:1555-1563. and P. F. Wareing. 1972. Seed dormancy in Acer pseudoplatanoides: The role of covering struc- tures. J. Expt. Bot. 23:813—829. Westwood, M. N. and N. E. Chestnut. 1964. Rest period chilling requirement of Bartlett pear as related to Pyrus calleryana and P. communis rootstocks. Proc. Amer. Soc. Hort. Sci. 84:82-86. Wyman, D. 1971. Wyman's garden encyclopedia. The Macmillan Co., N. Y. M'llIIIIII‘IIIIIZIIIILIIfiiitittilltttittlis 2 9612