FACTORS I N F L U E N C I N G FRUIT S E T T I N G IN T H E P E C A N B y GUY WEBB ADRIANCE A THESIS P R E S E N T E D TO T H E G R A D U A T E SC H O O L OF M IC H IG A N S TA TE C O L L E G E OF A G R IC U L T U R E A N D A P P L IE D SC IE N C E IN PA RTIA L F U L F IL L M E N T OF R E Q U IR E M E N T S FOR T H E D E G R E E OF DOCTOR OF PH IL O SO P H Y H o rtic u ltu ra l D ep artm en t E a st L ansing, M ichigan !929 R e p rin ted for p riv ate circulation from T he B o ta n ic a l G a zette, Vol. X C I, N o. PR IN T ED IN T H E U .S .A . 2, April T9 3 ! ProQuest Number: 10008488 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. ProQuest. ProQuest 10008488 Published by ProQuest LLC (2016). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code Microform Edition © ProQuest LLC. ProQuest LLC. 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 4 8 1 0 6 - 1346 <3 K ip ip 0 , A li FACTORS IN F L U E N C IN G F R U IT S E T T IN G IN T H E P E C A N 1 G uy W. A d r i a n c e ( w ith s ix f ig u r e s ) Introduction This study was undertaken to gain information on the effects of some cultural practices affecting fruit setting in the pecan. Since pollination is essential to complete fruit developm ent in m any flowering plants, it has been studied in association w ith the m or­ phology and cytology of the developing nut. M a t e r ia l s a n d m ethods M o r p h o l o g y a n d c y t o l o g y . —For the study of the morphology and cytology of the developing pecan nut, collections of m aterial for imbedding were made at frequent intervals during the early growing season. The first samples were taken from swelling buds, and the next from tips of growing shoots, before the pistillate flowers actually appeared. Following the appearance of the pistillate flow­ ers, collections were made each day up to the time of receptivity and pollination; after which samples were taken a t 4-hour inter­ vals during the first day after pollination, then daily for 3 days, and then at 2-day intervals for 6 weeks. During the same period, samples which had been sacked and not pollinated were taken. In the later stages the shell of the n u t was too hard for sectioning, so nuts collected after 4 weeks were trim m ed w ith a knife to remove the hard shell. All m aterial was killed and fixed in medium chromo-acetic solution, and sectioned according to the paraffin method. The most satisfactory stains used were Delafield’s haematoxylin, safranin-gentian violet, and acid fuchsin. The latter was satisfactory for staining pollen tubes. 1 S u b m itted to the G rad u ate F acu lty , M ichigan S ta te College, Ju n e 1929, in p a rtia l fulfillm ent of th e requirem ents for th e degree of D octor of Philosophy. P ublished w ith the approval of the D irector as C o n trib u tio n no. 86 of th e T echnical Series of th e T exas A gricultural E xperim ent S tation (Sci. P ap er no. 48, D iv. of H o rt.). Botanical G azette, vol. 91 144 A DR IA N C E— FRU IT SETTING 145 Some sections of very large fresh fruits were cut with a knife, killed in alcohol, cleared in acetone and cedar oil, and photographed w ith indirect light in thin glass cells filled with Canada balsam. F r u i t d r o p p i n g . —Field studies were undertaken with the idea of determ ining the am ount of shedding of young pecan fruits, the time of shedding, and the factors influencing this condition. P re­ lim inary observations and the work of other investigators indicated th a t the greater portion of the drop occurs early in the season. Records were taken of the dropping of the fruit during the period up to 6 weeks after time of pollination, on open-pollinated fruits and on fruits which were kept sacked until after all pollen was shed. Some further counts were made later in the season to check the rela­ tive im portance of the early drop. The position of the dropped nuts on th e peduncle was determ ined by the scar. These determinations were m ade twice a year, the proximal nut being counted as num ber “ 1” in all cases. B l o s s o m i n g h a b i t . — The first and last dates on which flowers were receptive was recorded for each tree. The period of receptivity was determ ined by the presence of a very perceptible viscous fluid on the stigm atic surface. The first and last dates on which pollen was shed were also recorded for each tree. The trees used for these records are in two orchards. The “old” orchard contains trees which were about 15 years old a t the beginning of the study, and had been bearing m oderately good crops. Seven varieties were used in this or­ chard, and from 3 to 12 trees of a variety, depending on the number available. In the “young” orchard the trees were 6 years old and beginning to bear well when the first data were taken in 1927. There were 10 varieties available in this orchard, and 8 or more trees of each variety. M e t e o r o l o g i c a l d a t a . — The d ata on tem perature and precipita­ tion were secured from the records of the M ain Station Farm , Texas Experim ent Station, which is about one-quarter of a mile from each orchard. Since, according to W o o d r o o f (35), S h u h a r t (30), and I s b e l l (10), the stam inate flowers are differentiated in the spring of the previous year and the pistillate flowers in the same spring in which they appear, it was not considered necessary to make records except for the late winter and spring, beginning January 1, of each 146 BOTANICAL GAZETTE [APRIL season, so as to give a sufficient margin before the beginning of growth. The tem perature records for the periods under consideration for each year have been converted into heat units, in order to have a definite basis for comparison. The rem ainder system of calculating the num ber of heat units above 40° F. was considered adequate for this study; the yearly total from January 1 to time of m aturity of stam inate and pistillate flowers was determ ined for each variety. The weekly, m onthly, and seasonal distribution of heat units and precipitation for each spring season were also calculated so th a t the effect of these factors on dichogamy m ight be determined. The work is concerned with the functioning of the plant over a period of years. The seasonal study is based upon a 5_y ear period, and an inspection of the meteorological records used shows th a t ex­ tremes of tem perature and rainfall were encountered during this time. Structure of flowers and fruits The morphology of the species of Carya has been treated by B e n ­ and W e l s f o r d ( 3 ) , N a w a s c h i n ( 2 5 ) , v a n T i e g h e m ( 3 3 ) , R o w l e e and H a s t i n g s ( 2 8 ) , d e C a n d o l l e ( 7 ) , M e e h a n ( 1 6 ) , L u b b o c k ( 1 4 ) , B r a u n ( 6 ) , N i c o l o f f ( 2 6 ) , and others. B i l l i n g s ( 4 ) and W o o d r o o f ( 3 7 ) worked with the pecan specifically. F l o w e r i n g h a b i t . —W ith regard to the production of stam inate flowers, W o o d r o o f ( 3 5 ) and I s b e l l ( 1 0 ) state th a t the catkins are formed within the bud in early spring, the process probably extend­ ing through April and May. In any case the stam inate flowers are differentiated early in the growing season a full year previous to their appearance, and there is no chance for a deficiency of pollen due to retarded differentiation of stamens. In 1928 a B urkett tree at College Station had two clusters of pistillate flowers sacked after all catkins around the basal portion had been removed. When the sacks were later removed, it was noticed th at one lateral bud on each of the new shoots had produced a group of catkins. Since these cat­ kins were on current season’s growth, they had certainly been differ­ entiated just previous to their appearance. The catkins appeared normal but were too late to be of any value in producing pollen for the current season. The stigmas had all dried several weeks previous­ ly, while the catkins were still green and im m ature. so n A DR IA N C E— FRU IT SETTING !47 W o o d r o o f and W o o d r o o f ( 3 6 ) state th at the pistillate flowers are norm ally differentiated from the term inal buds of the previous sea­ son b u t m ay be produced from lateral buds. S h u h a r t ( 3 0 ) gives three cases of false term inal buds which produced pistillate flowers, and m aintains th a t the true term inal bud is strictly vegetative. I t has been observed at College Station th a t few true term inal buds are produced, and the greater p art of the pistillate flowers arise from lateral buds near the apical end of the shoot. Buds rendered subterm inal in position by cutting back the dorm ant shoot have in practically all cases produced pistillate flowers. D etailed study of the structure of the n u t in various stages of developm ent showed the following facts: 1. The middle septum of the n u t is parallel to the axis of the inflorescence, and the plane of the stigmas is also parallel to this axis. In the walnut, although the plane is parallel to the axis, as in the pecan, the middle septum is perpendicular to this axis. 2. The peculiar branching of the vascular system of the walnut, as described by N i c o l o f f ( 2 6 ) but not previously figured for the pecan, is clearly shown in this species (figs. 1, 2). N i c o l o f f states th a t anterior and posterior to the ovule the placenta produces two bodies, in the form of horns, which are not an integum ent as has been represented. The ovule, exactly term inal, according to N i c o l o f f , is supplied w ith symmetrical vascular connections from both sides by vessels (and also phloem) which come from the lateral bundles of th e transverse partition, running to a point just below the ovule, and turning back to enter the integum ent. The development and the anatom y of the ovule, in his opinion, show th a t this organ has an axil dependence and not a carpellary dependence (cauline instead of foliar). 3. A vertical partition (middle septum) supports the orthotropous, sessile ovule, which has only one integum ent (figs. 1,2). After fertilization, the cotyledons expand downward on either side of the partition, away from the micropyle. In the walnut ( 2 6 ) the ovary, a t first unilocular, becomes a t the time of fertilization quadrilocular in its basal portion, and also in its upper portion; this tendency is observed to a slight extent in the basal portion of the pecan. 4. T he normal bearing habit of the pecan a t College Station is the production from a single compound bud, lateral and usually 148 BOTANICAL GAZETTE [APRIL subterminal, which separates as three buds when the heavy outer bud scales are pushed off in the spring. From the two outer buds, F ig s. i , 2.— Fig. 1, longitudinal view of n u t in plane of septum 6 w eeks a fte r pollina­ tion. show ing gross m orphology an d portion of vascular connection of ovule; fig. 2, longitudinal view of n u t perpendicular to septum , 6 w eeks afte r pollination; X iK. two clusters of three catkins each arise with a central shoot, coming from the bud between these two clusters, which term inates in a pis­ tillate inflorescence. This is not in harm ony with the common con­ ADR IA N C E— FRU IT SETTING 149 ception th a t the stam inate flowers arise from lateral buds and the pistillate flowers from term inal buds (fig. 3). F i g s . 3 - 6 . — Fig. 3, la te ra l b u d of pecan a t tim e of swelling in M arch, show ing two clusters of catk in s an d cen tral shoot w ith p istillate prim ordia, X 18; fig. 4, ovule a t tim e of p o llin atio n , show ing in teg u m en t n o t y e t inclosing nucellus, X 4 5 ; 5> enlarged view of ovule 3 weeks afte r pollination, showing fertilized egg an d disintegrated synergids, X 19 8 ; fig. 6, term in a tio n of p istillate flower cluster, showing one norm al and two ab o rtiv e flowers, w hich will shrivel a n d drop a b o u t tim e of pollination, X 18. BOTANICAL GAZETTE [APRIL 5. In the case of the S tuart pecan, small anther-like structures were observed on the flower axis at the bases of individual pistillate flowers. This condition was observed in two clusters, and no previ­ ous record of such structure has been found. Pollination and fertilization Chalazogamy, first observed by T r e u b ( 3 4 ) in Casuarina suberosa, is recorded by B e n s o n ( 2 ) for Betula, Alnus, Corylus, and Carpinus; by N a w a s c h i n ( 2 4 , 2 5 ) for Juglans regia and Corylus avellana; by B i l l i n g s ( 4 ) in m aterial of Carya olivaefonnis, collected a few days after the withering of the anthers; and by W o o d r o o f and W o o d ­ r o o f (37), also in the pecan. The w riter’s observations show th a t a t the time of pollination the ovule is not completely surrounded by the integum ent, although it is later so inclosed. The pollen tube grows inward through the tissue of the stigma until near the central region of the style, and then grows downward, not in the stylar canal, b u t along the general course of its vascular tissues. I t appears to go down to the chalazal region in various ways, usually in the wall of the ovary. In one case a pollen tube was unm istakably grow­ ing downward through the integum ent. The ovule a t the time of pollination is small and relatively unde­ veloped, and is not yet surrounded by the integum ent (fig. 4). Two weeks later the ovule is surrounded by the integum ent, the mega­ spore m other cell is discerned, and pollen tubes are present in the nucellus. There is considerable difference a t this stage between the pollinated and unpollinated ovules. Although the evidence shows th a t considerable time elapses between pollination and fertilization, pollination is prom ptly followed by germination of the pollen grains, growth of the pollen tubes, and this in turn by progressive changes in the several ovarian and ovular tissues. Fig. 5 shows an ovule 3 weeks after pollination. S t e r il it y Sterility in plants has been the object of a considerable num ber of investigations, m any of which indicate lack of pollination to be a factor of considerable im portance. S a v a s t a n o (29) and S ta n c a n e l l i (31) record cases of sterility in pistache and filbert, both of I 93i] A D R IA N C E — FRUIT SETTING 151 which are wind-pollinated n u t fruits, where lack of pollination and fertilization was given as the cause. There is evidence to show th a t sterility in the pecan is due to lack of viable pollen rath er than to self- or inter-incom patibility. R egard­ ing sterility in th e pecan in Georgia, S t u c k e y ( 3 2 ) states th a t self­ sterility is due prim arily to the interval in tim e between the recep­ tive stage of the pistillate flowers and the shedding of pollen. This type of self-sterility, lack of self-pollination instead of true self­ sterility or incom patibility, is not the usual condition in commercial fruit plants. M o r r i s (21) showed th a t eight varieties of the pecan gave an average of 74 per cent set when self-pollinated, and th a t most of the varieties gave a good set if the pollen was shed shortly before or during recep tivity; b u t when shed early in the season it was not ef­ fective on the latest-m aturing stigmas. F a c t o r s a e f e c t i n g f r u i t s h e d d i n g .—I t is apparently possible to distinguish three distinct periods of dropping in the orchards at College Station: (1) a t time of pollination; (2) 2-4 weeks after pol­ lination ; (3) a t irregular intervals during the remainder of the grow­ ing period. W ith regard to the first condition, certain flower clusters shrivel and dry w ith the young nuts or flowers still attached to the peduncle. In other clusters, or in fact in nearly all clusters, there are one to three im m ature nuts a t the apical end which shed along w ith th e tip of th e peduncle about the time of pollination. This last m entioned type of shedding, however, still leaves a sufficiently large d u ste r of n uts to produce a good crop. The shriveling of entire clus­ ters has not been observed to any great extent, but the disturbed n u tritive conditions following over-production m ight be responsible for such a condition, as explained by W o o d r o o f , W o o d r o o f , and B a i l e y (38). T he varieties Delmas and B urkett, used in this work, have borne good crops every year during the course of this study, and there has been no opportunity to observe “off” years. T he second type of dropping, referred to as the “M ay drop” (38), since it has been observed to occur 2-4 weeks following pollina­ tion in April and M ay, has proved of greatest significance in this study. W o o d r o o f and W o o d r o o f (37) state th a t fertilization oc­ curs 2-4 weeks following pollination. The am ount of this second BOTANICAL GAZETTE ! 52 [APRIL drop ranged from n to 52 per cent generally to 20 to 30 per cent, as indicated in table I. The third drop later in the season, due presum ably to environ­ m ental factors, does not am ount to a large percentage of the total drop. The d ata in table I, showing the to tal drop to July 15 (about TABLE I A m ount or d r o p u n d e r c o n d itio n s o f o p e n p o lli n a t i o n Total nuts 1929 1928 1927 Variety 1927-1929 Percentage dropped Total nuts Percentage dropped Total nuts Percentage dropped Four weeks after pollination Schley.................................. Texas Prolific...................... Delmas................................. Burkett................................ Rome................................... Success................................. San. Saba..................... Stuart.................................. Moneymaker....................... All varieties..................... 119 301 363 383 209 87 II IO 23 19 52 17 303 527 498 388 328 420 22 22 27 26 2100 1980 17 41 23 23 20 29 23 To July 15 Delmas......... ...................... Burkett................................ San Saba............................. Stuart................................... Texas Prolific...................... Moneymaker....................... All varieties. .*................. 527 388 328 303 420 35 36 1980 24 48 28 26 23 29 36 10 weeks after pollination), and the work of B ilsing (5) which shows the drop for the entire summer, indicate th a t the early or “ M ay” fall m ay account for the greater p a rt of the seasonal drop. In the case of the unpollinated nuts, which were sacked before any pollen was shed and kept so until no more pollen was available, there appeared to be about the same am ount and character of drop during the first 3 weeks following pollination. A fter this tim e, how­ ever, the rate of dropping increased rapidly and the condition a t th e ADRXANCE— FR U IT SETTING I S3 end of th e fourth week is shown in table II. There were no unpol­ linated B u rk ett nuts to be found for collection the fifth week after pollination time, and, although the Delm as nuts persisted somewhat longer, there were only twelve of these unpollinated nuts after the sixth week. T he la tte r nuts persisting a t this time showed clearly defined abscission layers in all cases examined. A b s c i s s i o n . — Two general types of shedding were observed in D elm as and B urkett. In one case, which is less frequently observed, TABLE II E f f e c t of p o l l in a t io n and lack o f po l l in a t io n on ea rly DROP OF PE C AN S, 1 9 2 8 V ariety T otal NO. OF CLUSTERS P erc en ta g e of clusters in w hich num ber REMAINING AFTER 4 WEEKS WAS 0 I 2 4 3 of n u t s 5 6 I Sacked an d n o t pollinated D e lm a s.................. B u r k e t t ................. 392 373 32 69 7 5 is 6 20 18 9 7 7 3 I P ollinated D e lm a s.................. B u r k e t t ................. 253 0 250 6 7 5 21 31 28 10 11 28 34 13 3 3 th e entire peduncle dries up, although the nuts persist. This occurs in the early stages of development of the cluster, usually within a few days after pollination. The nuts never attain the size they do in the case m entioned later. Shedding of the entire peduncle is due in nearly all cases to mechanical injury, such as insect damage or breakage by wind. The more common occurrence is the shedding of the individual flowers from th e peduncle. The nuts in the cluster do not shed all a t the same time, although there does not appear to be any regular order for the drop. Even after all the nuts have dropped from the peduncle, it persists in a green condition for a period of several weeks. The evidence presented by the basal region of unpollinated nuts indicates th a t the abscission layer is well defined within 3 weeks after receptivity. The abscission appears to be produced in the char­ i 54 BOTANICAL GAZETTE [APRIL acteristic m anner, as described by H a n n i g ( 9 ) , L l o y d ( 1 2 , 1 3 ) , and for various nut fruits, not including the pecan. The walls of the cells in the separation layer are softened and the cells grow longitudinally, producing considerable displacement and disruption of the tissues. The d ata presented in tables I and I I indicate th a t the latter type of drop, the shedding of the separate nuts from the peduncle, follows pollination. The few unpollinated nuts in the controlled experiments which persisted after the 6-week period m ay actually have been pol­ linated accidentally, or m ay have developed parthenocarpically. There are sometimes a few seedless pecans, which m ight be account­ ed for on this basis. E f f e c t u p o n s h e d d i n g o f p e d u n c l e p o s i t i o n . —Prelim inary studies were made to determine the relative ability of the nuts in different positions on the peduncle to set and m ature. A large num ­ ber of clusters were treated in the following ways: (1) pollination of two basal flowers only; (2) pollination of two term inal flowers only; (3) pollination of two term inal flowers and snipping off basal flowers; (4) pollination of one basal and one term inal flower. Considerable difficulty was encountered in this work, owing to the lightness of the pollen, which made it almost impossible to keep it from the other flowers in the cluster. A num ber of pollinations were made as out­ lined, after the nuts to be left unpollinated had been covered with small gelatin capsules. Because of high winds, m ost of these capsules were shaken off and the nuts pollinated from loose pollen in the bags. I t was also attem pted to kill the stigmatic surface of the nuts not to be pollinated with osmic acid. The results in both cases were of questionable value and are not included. L ater studies on open pollinated clusters, however, show th a t there is a rather definite relationship between the position of the n u t in the cluster and the probability of its shedding. Table I I I indicates th a t in clusters of varying num bers the basal n u t or flower is much more likely to be dropped than any other. The position next to the basal is the one showing the next largest percentage of drop, and the apical n u t or flower third. The percentages of drop in the respec­ tive positions are 13, 7, and 4.5. Those nuts in interm ediate posi­ tions are much less likely to drop. These d ata are not in accord with N a m ik a w a (2 2 , 23) ADRIANCE—FRUIT SETTING *55 those given by W o o d r o o f , W o o d r o o f , and B a il e y (38), who found the num ber of nuts to the cluster influenced th e position of shedding. I t is frequently observed w ith th e pecans a t College Station, howTABLE III R e l a t io n b e t w e e n p o s it io n o f n u t i n c l u s t e r a n d s h e d d i n g P ercentage Variety No. OF NUTS 1 2 (basal) shed to 3 J uly 2, 1928 4 s 6 Clusters of 6 nuts Delmas.................... Burkett................... San Saba................. Moneymaker.......... 264 IS6 Total................... 8 48 12 14 18 14 3 2 4 0 480 13 8 2 8 3 6 2 0 2 3 4 5 6 Clusters of 5 nuts Delmas.................... Burkett........... San Saba............. Stuart...................... Moneymaker.......... 215 250 90 So no 13 14 12 16 10 Total.................... 715 13 9 4 5 3 4 5 5 0 2 10 3 0 7 4 10 5 6 4 5 Clusters of 4 nuts Delmas.................... Burkett................... San Saba................. Stuart...................... Texas Prolific.......... Moneymaker.......... Total.................... 40 76 204 144 116 200 780 17 20 n 8 20 5 8 8 s 4 2 4 1 5 7 4 s 5 1 3 13 ■ 7 3 3 13 6 3 4 Clusters of 3 nuts Delmas.................... Burkett................... San Saba................. Stuart...................... Texas Prolific.. . . . . Moneymaker.......... T otal................... 0 84 87 123 11 20 12 12 16 7 *3 54 372 9 15 6 11 0 5 6 5 7 11 4 13 8 4 2 ---- — • 156 BOTANICAL GAZETTE [APRIL ever, th a t the basal nut does not always complete its developm ent in time for pollination, and the heavy shedding from this position m ay be attrib u ted to lack of pollination. W ithin the pistillate inflorescence, the different flowers of the cluster are at the same stage of development at the time of pollina­ tion, except for the smaller ones noted later. I t has not been possible to fix a different time of receptivity for the different flowers of normal size in the cluster. According to W o o d r o o f and W o o d r o o f (37), the basal flowTers are differentiated first, and there are always some undeveloped flowers a t the apex of each cluster. These flowers are normal b u t not far enough advanced to be receptive, and are shed soon after the period of pollination (fig. 6). I t has been observed in several cases, especially with Texas Prolific, th a t there are sometimes one or two im m ature flowers a t the base of the cluster; these have always been observed to fall w ithout reaching the stage for pollina­ tion. W o o d r o o f and W o o d r o o f (37) illustrate this characteris­ tic, b u t state th a t such flowers may develop into nuts. A careful consideration of the preceding d ata seems to w arrant the following interpretations: (1) The so-called “ M ay ” drop of pe­ cans occurring 2-4 weeks after pollination accounts for the greater portion of the total drop, except those which are dam aged by insects and diseases, or drop later as the result of drought. (2) This “ M ay” drop appears to be the result of lack of fertilization of the flowers, due primarily to lack of pollination, since it coincides with the drop of sacked unpollinated flowers. (3) A proper supply of pollen at the time the pistillate flowers are receptive is the prim ary requisite for setting and development of the nuts. In view of the fact th a t pollination seems to be the limiting factor in determining the set of fruit in the pecan, a consideration of the factors influencing pollination is of prim ary im portance. Since di­ chogamy nearly always occurs in monoecious or dioecious plants, investigations of this condition were made in the case of the pecan. D ic h o g a m y The factors of prim ary im portance in the consideration of di­ chogamy are the character and extent of the difference in tim e of m aturity of pistillate and stam inate flowers, and th e factors which ADRIANCE—FRUIT SETTING I931l I 57 influence this difference in maturity. K erner and Oliver ( i i ) state that all monoecious plants are protogynous, although other workers (15-20, 27) have shown that protogyny is not always the rule in the nut fruits. Stuckey (32) divided the pecan varieties into two groups on the basis of dichogamy, stating that in group I the pistillate flow­ ers of most varieties become receptive at the same time that the TABLE IV R a n g e o f m a t u r it y o f p e c a n f l o w e r s , M arch 31; e . g ., 1 9 2 5 - 2 9 (d a y s A p r il 1 0 = 1 0 , M ay Staminate Variety 192s 1926 after 10=40) Pistillate 1927 *1928 1929 1925 1926 1927 1928 1929 Old orchard Texas Prolific.............. San Saba...................... Delmas......................... Stuart........................... Moneymaker............... Bolton.......................... Rome............................ 9-16 21-26 9- i 5 27-32 14-21 31-38 14-24 30-38 17-21 31-37 9-17 28-34 9- I 3 24-28 10-15 20-30 9-14 10-16 24-34 11-20 17-23 3 i - 4 o 20-25 18-30 35-43 21-26 14-20 29-37 16-21 13-20 27-35 16-22 10-15 24-32 n -1 9 11-22 31-40 n -2 3 33-38 8-15 32-37 12-24 34-40 10-17 31-35 7-12 26-28 8-13 30-35 17-21 17-24 19-20 19-22 24-34 9- i 5 28-39 23-32 28-36 14-15 24-30 13-14 23-28 18-20 25-35 11-21 10-18 10-20 11-19 9- i 5 9- i 5 1 9 -2 1 1 2 -1 3 2 6 -3 0 2 2 -2 5 2 1 -2 6 1 8 -2 1 2 4 -3 0 1 0 -1 8 1 0 -1 8 1 3 -1 9 1 4 -2 0 1 0 -1 4 9 -1 7 1 1 -1 6 1 0 -1 4 1 1 -1 6 1 0 -2 0 Young orchard Schley............... Moneymaker... Success.............. Alley................. Moore............... Burkett............. Onliwon............ Atwater............ Western Schley. Delmas............. 1 7 - 2 8 33-39 1 4 -2 1 2 8 - 3 6 2 6 - 2 8 32-39 11-21 2 4 -3 2 8 -1 4 2 2 -3 0 1 7 -2 8 3 2 -4 0 1 1 - 1 9 2 6 -3 3 1 9 -2 4 2 0 -2 7 1 7 -2 2 1 1 -1 6 7- i 3 20-26 1 4 -1 8 33-40 2 0 - 2 5 29-34 1 4 - 1 9 1 5 -2 0 1 7 -3 0 3 2 -4 1 2 0 -2 6 2 4 -2 8 1 9 -2 1 stam inate flowers shed their pollen, while in group I I the pistillate flowers become receptive 2-10 days before the stam inate flowers shed their pollen. T he blossoming d ata in table IV show th a t the type of dichogamy in th e pecan is not always fixed, and d ata in table V m ake it evident th a t there is a strong tendency in certain seasons toward protandry and in others tow ard protogyny. Some of the m ost im portant com­ mercial varieties, as Delmas, Schley, Stuart, and B urkett, respond 158 BOTANICAL GAZETTE [april to these seasonal tendencies. I t is also shown (table V) th a t there is a group of varieties which have a positive tendency tow ard protandry, which tendency has not been observed by previous investiga­ tors. Texas Prolific, San Saba, Moore, and Alley were protandrous every year. Another group shows a positive trend tow ard pro­ togyny, although this is not so strongly m arked as in the protandrous TABLE V Character a n d e x t e n t i n d a y s o f d ic h o g a m y ; + in d ic a t in g PROTOGYNY AND — PROTANDRY Variety 192s 1926 1927 1928 1929 Old orchard Texas Prolific..................... San Saba............................ Delmas............................... Stuart................................. Moneymaker..................... Bolton................................. Rome.................................. 2— 2— 6 -f2+ 7+ 2+ 1+ 10— 6 1— 4“ 0 2+ 6- 79- 4“ 2— 1— 0 1+ 8 - 6+ 6+ 5+ 4+ 2+ 4- 0 0 io-f11 + 5+ 7+ 4- Young orchard Schley................................. Moneymaker. .................... Success............................... Alley................................. Moore................................. Burkett.......................... Onliwon.............................. Atwater.............................. Western Schley.................. Delmas............................... 2— 2-jO 9+ 9+ 1+ 7+ 10+ 8+ 1 1 -f- 8+ 10+ 7+ 10+ 4+ 1313- 2— 3+ 3+ group. M oneymaker, Success, and Bolton were protogynous in al­ m ost every case through the entire period; M oneym aker in 1926 and 1927, and Success in 1927, m atured stam inate and pistillate flowers on the same date. In view of these facts, it seems advisable to depart from previous classifications, and make three groups of pecan varieties as regards dichogamy: protandrous, fluctuating, and protogynous. S e a s o n a l t e n d e n c i e s .—The behavior of th e fluctuating varie­ ties, as well as the tendency of the positive varieties tow ard over­ A D R IA N C E — F R U IT SETTING 159 lapping in blossoming, indicate th a t the seasons of 1925, 1928, and 1929 exerted some influence tow ard protogyny; the seasons of 1926 and 1927 tow ard protandry. I t was considered advisable to ascer­ tain w hether these tendencies m ight be associated with definite con­ ditions of environm ent, as suggested by M e e h a n (16, 18). T he critical factors which m ight cause a difference in m aturity of th e flowers were considered to be tem perature and rainfall, although TABLE VI W e e k l y , m o n t h l y , a nd sea so n a l a ccu m u la tio n of h ea t u n its ABOVE D January 40° F . ate 7 ..................... i 5 9 -o 2 3 1 .0 1 8 8 .5 2 0 7 .0 3 2 0 .5 4 § 3-5 5 97- 5 3 09- 5 432-5 592- 5 7 8 1 .5 7 2 8 .5 ................. 9 ° i -5 1 1 0 3 .0 853-0 9 8 2 .0 1 8 ................................... 1 2 7 2 .5 1 0 6 7 .0 ................. 1 4 4 1 .0 1 ..................... 8 ..................... 4 ................................... 1 1 ................................... 1 8 ................................... 25 ................. 4 ................................... 11 25 April 1926 5i - o 74-0 2 8 ................................... March 1925 1 2 3 .0 ................. 14 2 1 ................................... February ( m e a n ) AT C O L L E G E S TA TI ON , ................. 15 2 2 ................................... 29 ................. 3 0 ................. 1927 1925-29 1929 1928* 2 0 .0 40.5 I IIO .O 2 6 9 .0 36- 5 279-5 3 2 6 .0 2 2 8 .0 3 2 1 .0 490-5 4 6 0 .0 3 6 8 .0 6 0 2 .5 5 7 0 .0 3 8 7 .5 729 . O 8 57- 5 6 2 5 5 6 8 6 .5 445-5 9 2 3 .0 7 8 1 .5 599- 5 1 0 6 9 .0 1 2 2 4 .0 9 6 1 .5 1 1 1 9 .0 1 2 4 9 .0 1 3 2 2 .5 1 2 4 1 .5 873-0 1 0 7 6 .5 1 6 4 4 .0 13^-5 1 5 2 4 .0 1422 0 1 3 1 4 .0 1843-5 2 0 8 1 .0 1487-5 1 6 2 1 .5 17 4 2 .0 1 5 9 0 .0 1573- 0 1977- 5 1 6 8 4 .0 1 7 8 6 .0 2 3 5 8 .0 1799-5 2 1 7 3 .0 i 857-5 2 0 1 6 .0 2 6 1 8 .5 1 9 8 2 .0 2 3 4 0 .0 2 0 2 0 .5 2 2 6 1 .5 2 6 3 2 .5 2 0 1 0 .0 2 3 7 2 .0 2 0 7 9 .5 2 3 0 2 .0 72 - 5 1 1 3 .0 1 6 6 .0 2 2 9 .0 4 9 4 .0 7 5 0 .0 * L e a p ye a r, F e b r u a r y 29 included in figures a n d d a t e ad v a n ce d one day, beginning M a rc h 3. wind and atm ospheric hum idity probably have considerable influ­ ence upon duration of receptivity of the stigmas and shedding of the pollen. In the consideration of the effect of tem perature, the num ber of h eat units above 40° F. mean was recorded for the first 4 m onths of each year, as described in the first p a rt of this work. These figures were arranged to show weekly, m onthly, and seasonal accumulations during the entire period (table V I). As shown by the totals on April 30, the year 1925 had the greatest num ber of heat units; 1927 and BOTANICAL GAZETTE i6 o [APRIL 1929 were about equal and considerably fewer th an 1925; and 1926 and 1928 had still fewer than the two last m entioned. The m onthly rainfall for the entire period and the weekly accum ­ ulations are shown in table V II. The rainfall in the three protogy­ nous seasons was considerably less th an in the protandrous seasons. For the protogynous seasons, 1925 had 4 inches, 1928 had 9 inches, TABLE VII W e e k ly , m o n th ly , a n d s e a s o n a l r a i n f a l l a t C o lle g e S t a t io n ( in c h e s ) 1 9 2 5 -2 9 Date January 7 .............................. 14........................ 21............................... 28.............................. February 4 .............................. 11................... ........ 18.............................. 25.............................. March 4 .............................. 11.............................. 18.............................. 25 ........................ April 1.............................. 8 .............................. 15 ........................ 22............................... 29.............................. IQ25 1926 1927 1928 1929 0,00 I .12 i -55 1.58 0.29 0. 29 0 35 o -39 2-53 4 -So 1.63 1.47 1.61 I .69 I .69 3-97 4-32 0,00 1.03 1.30 1.63 I . 72 4-37 4-37 4-58 458 3-44 3.58 3-58 2.67 2.67 5-12 7.80 8.48 10.46 3-55 355 3-55 355 4-17 12.62 12.69 13.96 16.37 16.61 1.77 1.77 2. 17 234 2.34 2.35 4.84 5°9 5-24 5 -9 ° 5-95 4.70 6.26 7.88 9.07 9.07 10.76 4.70 1.92 7.04 10.76 10.77 14.69 16.91 6.99 7.64 17-39 597 6.61 6,69 9-74 983 983 7-99 8.92 8.94 9.71 10.68 10.69 10.69 and 1929 had 10 inches. For the protandrous years, 1926 had 17 inches, and 1927 had 17 inches. The weekly accum ulations give a better idea as to the distribution of this rainfall. W hen the combined effect of tem perature and rainfall is consid­ ered, it m ay be observed th a t these two factors compensate for each other to some extent. The season of 1925, which was very hot and very dry, was not so strongly protogynous as the season of 1928, which was much cooler and had more rainfall. In the same way the season of 1929, which was even more strongly protogynous than 1928, had very little more rainfall th an 1928, and was m uch cooler up to the early p art of April. The greater to tal of heat units is ac­ A DR IAN C E— FRU IT SETTING 161 counted for by the sustained high tem perature in April, after many of the trees had blossomed. In th e two protandrous seasons of 1926 and 1927, however, there was no observed difference in blossoming which m ight be attributed to the difference in heat unis. The heavy rainfall is the only out­ standing factor which is common to these two seasons. W hen th e h eat units to date of m aturity are considered, as shown in table V III, two facts stand out: 1. On th e basis of the means, there is a much greater variation in any one year between varieties in num ber of h eat units to m aturity of stam inate flowers th an to m aturity of pistillate flowers. To ex­ press the same behavior in a different way, there is less difference in the d ate of blossoming of pistillate flowers than of- stam inate. This same difference is apparent in both the old and the young orchards, where both age and variety of the trees are different. The sig­ nificance of these differences is greater from the fact th a t Delmas and M oneym aker, the only two varieties occurring in both orchards, check closely in their requirements. 2. T he pistillate flowers vary much more from year to year in th eir total requirem ents than do the stam inate flowers, the greatest coefficient of variability for stam inate flowers, 6.1, being less than th e least coefficient for pistillate flowers, 6.7. The actual range in the coefficient of variability for the stam inate flowers of the different varieties is from 2.3 to 6.1, and for the pistillate flowers, 6.7 to 9.5. As shown in table IX , the odds in favor of the significance of this difference are 999 to 1. W ith regard to all the observations recorded, it m ay be stated th a t the conditions of environm ent in the spring exert considerable influence on blossoming of the pecan. In general it appears that, al­ though th e d ate of m aturity of both stam inate and pistillate flowers is influenced by favorable conditions for growth in the spring, the stam inate flowers respond more readily than the pistillate flowers. This fact would indicate a possibility th a t seasons favorable for early growth m ight be favorable for protandry. A d r i a n c e ( i ) has previously presented d ata showing some effects of spring tem pera­ tures in this respect. In confirmation of this idea, it m ay be stated th a t since the pis­ tillate flowers of the pecan are differentiated in the same spring th at BOTANICAL GAZETTE w r>- O'VO O' c^. CO 1O 0 0 W Os W + m -i -h -h + 1 VD O0 00 H 00 COSO so so H M t-^ 00 tJ- rt* 0 s o CO O O sO sO sO SO sO H H W M M so w O' H V) 0 Os H 0 w 0 w H H 00 H IO !>■* 00 H CO CO W 't ^ O O ' Os0 0 H H H H N 00 H ^ - 0 0 0 0 s o xr> 0 so so i n co 0 O 0 00 O w W W H W CO VO SO *0 o 00 00 00 O O Os O ' H H H W 'tN 0 w t"«. 0 O' W M CO w 10 w t^-oO M W W H M -st O ' w 0 00 00 W H H O' 00 t-*. H V) O O' H OS 0 0 Os 0 0 00 w O ' O' co POO f’O'O sO f"- J>-sO vO * 0 'O VO Os W H CO0 0 w OS r ^ o o H w H M tJ- CO Tj- H *$- ^ H CO O O ' h O ' w w *>■ n v> a o 1 0 1 0 0 0 00 0 0 o s Ov O '0 0 a s Os O O 0 w w h NOOOOO O O H 0 0 OS M W W H H VO VO +1 +1 SOvO SO O w 00 O' O' O N 0 W W \r> w 00 cocoCO lo v o 00 W 00 O' H H M O O W CO J>* SO CO N xn w 00 00 c o CO d1^ 00 00 H H O H O W *too N H Q 0 N Tt’ CO QS w 10 O h SO O ' 0 t-* w H H CO00 1 0 cO H 00 s o OsvO Texas Prol San Saba. Stuart.. .. Bolton..,. Rome. . . . 162 CO >, ft -S'8 COCOAS do < -