Ovary starch reserves and pistil development in avocado (Persea americana)

In avocado, only a very small fraction of the flowers are able to set fruit. Previous work in other woody perennial plant species has shown the importance of carbohydrates accumulated in the flower in the reproductive process. Thus, in order to explore the implications of the nutritive status of the flower in the reproductive process in avocado, the starch content in the pistil has been examined in individual pollinated and non‐pollinated flowers at anthesis and during the days following anthesis. Starch content in different pistilar tissues in each flower was quantified with the help of an image analysis system attached to a microscope. Flowers at anthesis were rich in highly compartmentalized starch. Although no external morphological differences could be observed among flowers, the starch content varied widely at flower opening. Starch content in the ovary is largely independent of flower size because these differences were not correlated with ovary size. Differences in the progress of starch accumulation within the ovule integuments between pollinated and non‐pollinated flowers occurred concomitantly with the triggering of the progamic phase. The results suggest that starch reserves in the ovary could play a significant role in the reproductive process in avocado.     

Pistil Starch Reserves at Anthesis Correlate with Final Flower Fate in Avocado (Persea americana)

A common observation in different plant species is a massive abscission of flowers and fruitlets even after adequate pollination, but little is known as to the reason for this drop. Previous research has shown the importance of nutritive reserves accumulated in the flower on fertilization success and initial fruit development but direct evidence has been elusive. Avocado (Persea americana) is an extreme case of a species with a very low fruit to flower ratio. In this work, the implications of starch content in the avocado flower on the subsequent fruit set are explored. Firstly, starch content in individual ovaries was analysed from two populations of flowers with a different fruit set capacity showing that the flowers from the population that resulted in a higher percentage of fruit set contained significantly more starch. Secondly, in a different set of flowers, the style of each flower was excised one day after pollination, once the pollen tubes had reached the base of the style, and individually fixed for starch content analysis under the microscope once the fate of its corresponding ovary (that remained in the tree) was known. A high variability in starch content in the style was found among flowers, with some flowers having starch content up to 1,000 times higher than others, and the flowers that successfully developed into fruits presented significantly higher starch content in the style at anthesis than those that abscised. The relationship between starch content in the ovary and the capacity of set of the flower together with the correlation found between the starch content in the style and the fate of the ovary support the hypothesis that the carbohydrate reserves accumulated in the flower at anthesis are related to subsequent abscission or retention of the developing fruit.     

Morphological and cytological development and starch accumulation in hermaphrodite and staminate flowers of olive (Olea europaea L.)

In olive (Olea europaea L.), the formation of functionally staminate flowers rather than fully functional hermaphrodites is one of the major factors limiting fruit set, as flowers with aborted pistils are incapable of producing fruit. Studies conducted on various angiosperm species have shown a correlation between flower abortion and starch content. Thus, it is important to know if starch content plays a role in regulating pistil development in olive and if so, what mechanism regulates starch distribution. Cyto-histological observations of staminate and hermaphrodite olive flowers show that pistil development in staminate flowers is interrupted after the differentiation of the megaspore mother cell. At that stage, starch grains were only detected in the ovary, style and stigma of the hermaphrodite flowers. No starch was observed in the pistils of the staminate flowers. This finding suggests a tight correlation between starch content and pistil development. The secondary origin of starch within the flower is indicated by low chlorophyll content in the gynoecium, undetectable Rubisco activity in the pistils of these two kinds of flowers and by the ultrastructure of the plastids observed by transmission electron microscope analysis. The plastids have few thylakoid membranes and grana and in the staminate flowers appeared very similar to proplastids. Considering differences in starch content between staminate and hermaphrodite flowers and the secondary origin of the starch, differences in pistil development in the staminate and hermaphrodite flowers could be related to differences in the sink strength of these two types of flowers.     

荆条花蜜腺发育解剖学研究

荆条（Ｖｉｔｅｘ ｃｈｉｎｅｎｓｉｓ Ｍｉｌｌ．）花蜜腺属于淀粉型子房蜜腺,呈圆筒状环绕于子房的基部。蜜腺外观上无特殊结构,表面有。由分泌表皮和泌蜜组织组成,包括分泌表皮、气孔器、泌蜜薄壁组织和维管束。密腺和子房壁起源相同。花蕾膨大期,泌蜜组织细胞中产生大液泡;露冠期,泌蜜组织中形成维管束;花蕾初放期,分泌表皮细胞分化形成气孔器,无气孔下室,淀粉粒的积累在此期达到高峰;盛花期,蜜腺中已无淀粉粒,密     

The transmitting tract in Trimezia fosteriana (Iridaceae).

Observations of the transmitting tract cells in Trimezia fosteriana were made from the pre-secretory stage until anthesis. Secretory products appear about 14 days before anthesis in all parts of the pistil. Simultaneously starch disappears from the plastids and the dictyosomes are surrounded by more and larger vesicles than before. In the beginning of the secretory stage multivesicular bodies may be in contact with ER profiles and an ER origin is therefore presumed. Later during the secretory stage the multivesicular bodies are larger and more abundant. Their envelope is often partly fused with the plasma membrane and vesicle swarms are common on the outside of it. Close to flower opening many organelles change in appearence. RER becomes more abundant and the mitochondrial matrix highly electron dense and the cristae expanded. Starch grains reappear and large ones are common in the stigma and ovary plastids. The dictyosomes are numerous and surrounded by the largest vesicles observed during the secretory stage. Osmiophilic granules are common in the dictyo-some vesicles and under the cell walls abutting the transmitting tract. In the ovary they are present one week before anthesis. In the stigma and style corresponding granules of high electron density appears at the day of flower opening. The extracellular secretory product contains fibrillar and granular substances consisting of carbohydrates, including pectic substances, and proteins.     

Influence of intraovular reserves on ovule fate in apricot (Prunus armeniaca L.)

 In many plant species with multiovulate ovaries, a considerable reduction in the number of ovules takes place. However, the underlying physiological causes are not clear. In Prunus spp., although flowers present two ovules, usually only one seed is produced. We have followed the development and degeneration of the two ovules in apricot (Prunus armeniaca L.) and examined the extent to which carbohydrates within the ovule might be involved in determining the fate of the ovule. While the primary ovule grows in the days following anthesis, growth of the secondary ovule is arrested. Starch distribution along the different ovular tissues exhibits several changes that are different in the two ovules. Primary ovule growth is inversely related to starch content and this growth takes place independently of pollination since it occurs in the same way in pollinated and unpollinated flowers. In the secondary ovule, starch disappears simultaneously from all ovular structures and callose is layered at the chalazal end of the nucellus. The size of the secondary ovule does not change significantly from anthesis to degeneration, and callose starts to accumulate 5 days after anthesis. Likewise, this process occurs independently of pollination. These results are discussed in terms of the implications of the starch content of ovules in fertilization success and ovule fate. Received: 26 August 1997 / Revision accepted: 17 December 1997     

Proteins, non-structural carbohydrates and organic acids in the flowers of sweet orange (Citrus sinensis (L.) osbeck)

The concentration of soluble proteins in open flowers of sweet orange (Citrus sinensis (L.) Osbeck) was about 35% of the protein content found in green leaves, while ovary and stigma, with attached style, contained up to 85%. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) indicates that flowers and leaves contained ribulose bisphosphate carboxylase-oxygenase (Rubisco). At least 12 polypeptides, ranging from 22 to 100 kDa, were more distinct in flowers than in leaves. The polypeptide band at about 100 kDa in the flower extract suggests the presence of phosphoenolpyruvate carboxylase (PEPCase) in citrus flowers. Activity of Rubisco and PEPCase, expressed in μmol g tissue fresh weight⁻¹ hr⁻¹, averaged 14.2 and 64.6 for intact open flowers, and 547.9 and 63.3 for the leaves, respectively. Starch and reducing sugars were 1.2- and 8.4-fold higher, respectively, and dark respiration rates were about five-fold greater for open flowers than fully expanded, sun leaves. Quinic and malic acids made up about 96% of the organic acids found in flowers and leaves. Ascorbic, citric, fumaric, and shikimic acids were in small or trace amounts. The large accumulation of starch and soluble sugars, in addition to the presence and activity of Rubisco and PEPCase, indicates that the flowers of sweet orange would have some capability to perform photosynthetic CO₂ assimilation, the metabolites of which might play some important role in flower development and fruit setting.     

Effect of ovular receptivity on seed set and fruit development in cucumber (Cucumis sativus L.)

Summary Seed set and fruit development in cucumber (Cucumis sativus L.) were studied in relation to female flower receptivity from day — 2 before anthesis to day + 2 after anthesis. The female cucumber flower is protogynous. The pistil was receptive 2 days before anthesis. The iso-electric focusing (IEF) patterns of the stigma/style proteins, were identical from day -5 to day +2. In pollinated flowers in vivo germination and pollen-tube growth in the ovary were affected by pistil age from day -2 to day +2. In addition, differences in sectorial filling in full seeds were observed within the fruits. A negative correlation was observed between the frequency of fertilized ovules in the pedoncular part of the fruit and ovary length at the time of pollination. In the whole fruit, significant differences in the number of full seeds and fruit size at maturity were found, and these were observed to be correlated with the various stages of female flower maturation at pollination. The day -2 and day +2 stages yielded the smallest fruits with few full seeds compared to the day -1, day 0 and day +1 stages, which had the biggest fruits and a large number of full seeds. A strong positive correlation was found between total seed number (including full and empty seeds), fruit length and weight at maturity. All these results suggest that both seed set in the different parts of the fruit and fruit development are controlled by ovular receptivity rather than by stigma/style receptivity.     

Biochemical characterization of soybean ovary growth from anthesis to abscission of aborting ovaries

Soybean (Glycine max [L.] Merr.) ovary growth was measured from anthesis to 6 days after anthesis (DAA) to establish a timetable of biochemical events that might be useful in identifying processes that initiate abscission. Two procedures were developed to provide samples with either high or low percent pod set for `IX93-100,' a semideterminate line having long racemes. Characteristics measured were fresh and dry weight, soluble and insoluble protein, soluble carbohydrate, starch, RNA, and DNA. Setting ovaries grew more rapidly than abscising ovaries. Since there was a daily increase in ovary weight in both groups, all measured characteristics showed daily increases when expressed on perovary basis. Statistically significant differences between groups were detected between 2 and 5 DAA for most characteristics. When chemical composition was expressed on concentration basis, starch level was significantly higher in setting ovaries at 5 and 6 DAA. Regression analysis showed that these deviations between setting and abscising samples started between anthesis and 1 DAA. We conclude that processes leading to eventual shedding of fertilized ovaries (called flower abortion in soybeans) commence soon after anthesis of the shed flower, and that setting and abscising ovaries do not differ in protein, soluble carbohydrate, starch, or nucleic acid content when abscission processes begin.     

Pollen histochemistry and pollen : ovule ratios in Zingiberaceae

BACKGROUND AND AIMS: Pollen grains of 37 species from 11 genera in the family Zingiberaceae were examined to assess qualitatively starch or lipid contents; the pollen grain and ovule numbers per flower and pollen : ovule ratios were also counted and calculated. Pollen : ovule ratios were studied to reveal patterns of variation in the Zingiberaceae. METHODS: Freshly open flowers with dehiscing anthers were collected at random from plants growing in natural habitats or in botanical gardens. Presence of lipids or starch in pollen grains was tested by Sudan solution and IKI solution, respectively, and examined under a microscope. To estimate the pollen and ovule numbers per flower, one anther from each bud was carefully dissected and all pollen grains were counted; ovaries were carefully dissected out of each flower and counted. Whenever possible, at least 10-15 buds were used in the determination. KEY RESULTS: Thirty-three of all the 37 species examined had starchy pollen. Starch was not found in only four species and lipid was not found in only one species; among the four tribes in subfamily Zingiberoideae, all species of Zingibereae and Globbeae had pollen with no starch, Alpineae and Hedychieae had pollen with and without starch, whereas, all species of subfamily Costoideae had starchy pollen with abundant lipids. The mean pollen : ovule ratios in the members of the Zingiberaceae investigated range from 3.25 +/- 1.56 to 616.52 +/- 117.83. CONCLUSIONS: The pollen nutrition types seemed not related to mating systems. The pollen : ovule ratios in members of the Zingiberaceae with the same breeding system are noticeably lower than those recorded by previous authors. The lower pollen : ovule ratios in this family are presumed to be related to the highly efficient pollination systems, mediated by pollen which can be quite glutinous and the relatively large stigma area. In most of the Alpinia species the anaflexistylous flowers have much larger numbers of pollen grains and higher pollen : ovule ratios than the cataflexistylous flowers. There are significant differences in mean pollen grain numbers and pollen : ovule ratios between different life forms but ovule numbers are approximately the same.     

Pollen-pistil interaction in kiwifruit (Actinidia deliciosa; Actinidiaceae)

The pollen-pistil interaction has been examined in kiwifruit (Actinidia deliciosa). In this species a large number of seeds are produced in each fruit and a great many pollen grains germinate and grow to reach the ovules. This growth is assisted by an abundant secretion that is present all along the pistilar tract. At anthesis, the stigma is covered by a secretion where the pollen grains germinate and grow. The stylar transmitting tissue is initially rich in starch reserves, but the starch gradually disappears and, concomitantly, an abundant secretion that stains for carbohydrates appears in all of the intercellular spaces. Pollen tube growth relies on this secretion since it is depleted after pollen tube passage, while in unpollinated flowers it remains unaltered throughout the flower life-span. In the ovary a similar situation occurs. The placental surface, where the pollen tubes grow before reaching the ovules, is covered by a number of obturators. At anthesis, these obturators are rich in starch reserves and have an abundant secretion on their outer surface. As time passes, starch disappears while the secretion increases. It is in this secretion that the pollen tubes grow on their way toward the ovules. These observations are discussed in terms of the support given by the pistil to pollen tube growth to achieve the highly successful reproductive performance of this species.     

Flower morphology,nectar traits and pollinators of Cerinthe major (Boraginaceae-Lithospermeae)

In April and May 2010, a natural population of Cerinthe major (Boraginaceae-Lithospermeae) was investigated with regard to: floral morphology, phenology, sexual receptivity during anthesis, the production of nectar and its sugar and amino acid content. The pollinator array of this species was also investigated. Cerinthe major has showy, pentamerous, hermaphroditic flowers with a deep yellow corolla tube arranged on numerous scorpioid inflorescences. Nectar and pollen are the main floral rewards for pollinators. The arrangement of stamens limits access to nectar and promotes pollen loading onto pollinator bodies as they force their way towards the source of nectar. By limiting the direct exposure of nectar to the environment, the corolla tube and the arrangement of anther filaments seemingly protect nectar from evaporation resulting from high temperatures and low relative humidity during flower anthesis. The green, annular nectary located at the base of the ovary lobes is composed of a very thin epidermis enclosing a dense mass of parenchyma. The epidermis lacks stomata, and the thin cuticle has an irregular surface. The parenchyma cells do not store starch during the pre-secretory stage, suggesting that immediate photosynthesis is the most likely source of nectar carbohydrates. Generally, anthesis lasts 4–5 days; the gynoecium becomes fully receptive on the second day and this is synchronous with anther dehiscence. Since nectar production begins during the bud stage, a substantial volume is available for flower visitors at anthesis. Nectar production decreases drastically in senescent flowers and, if not consumed, the nectar can be re-absorbed. Analysis of sugars revealed a sucrose-dominant nectar (sucrose = 93.18 ± 1.35%). Proline, GABA, taurine, leucine, citrulline and alanine were the main amino acids present and are probably implicated in pollinator flight performance.     

First records of flower biology and pollination in African Annonaceae: Isolona, Piptostigma, Uvariodendron, Monodora and Uvariopsis

Seven species from five genera of Annonaceae were studied with regard to their flower biology and pollination in the Southwest Province of Cameroon, West Africa. They have protogynous hermaphroditic flowers, with exception of Uvariopsis species, which are monoecious. Fused petals of Isolona campanulata remain apically spreading and open during anthesis but form a deep basal urceolate tube around the reproductive organs. At anthesis the yellow pendent flowers emit a fruit-like scent and attracted small beetles, the likely pollinators. Piptostigma sp. flowers also emit a fruit-like scent but provide a closed pollination chamber formed by the three inner petals. Small staphylinid beetles attracted during the female stage of anthesis are released from the flowers at the end of the male stage 2-3 days later. Both species have diurnal anthesis, attracting and releasing the flower visitors during daytime. In contrast, Uvariodendron connivens and U. calophyllum have nocturnal anthesis with floral thermogenesis, produce spicy, aromatic and fruity scents and attract large Scarabaeidae beetles, the pollinators, along with many curculionid beetles, which were principally predators of the thick petals. The very large flowers of Monodora tenuifolia have yellowish petals which are spotted with dark red markings. Together with the sweetish, slightly disagreeable scent the flowers attract flies, principally dung flies. The two investigated Uvariopsis species are monoecious with pistillate and staminate flowers being functional at the same time. The violet red flowers of U. bakeriana visually seem to mimic the fruiting body of certain stinkhorn fungi (Phallaceae) although without producing their strong unpleasant carcass stench. Flower-visiting dung flies were rare. Conversely, U. congolana has a strong fungus-like scent, its flowers are presented at litter height and dung flies living in the litter were the flower visitors, albeit sporadic. The 4-5 days lasting anthesis of both Uvariopsis species appears to be an evolutionary consequence of their diffuse pollinator spectra. The studied African Annonaceae therefore have either cantharophilous or myiophilous/sapromyiophilous flowers with, in part, respectively, remarkably long anthesis, thermogenesis, and widely open, large flowers - all attributes unknown or rare in the hitherto better studied Neotropical Annonaceae.     

Flower bud differentiation and development in fruiting and non-fruiting shoots in relation to fruit set in apricot (Prunus armeniaca L.)

Situations of high flower bud drop and low fruit set without apparent causes are common in fruit trees. The term flower quality has been coined to explain differences among flowers in their capacity to set fruit, but the causes underpinning these differences are largely unknown. This lack of knowledge is based on the fact that these differences are established a posteriori and there are no criteria to determine a priori what will make a flower to set a fruit or to drop. In this work, we profit from the empirical knowledge that there are fruiting and non-fruiting shoots to explore to which extent flower bud differentiation and bud development will affect the subsequent fruit set. For this purpose, the processes from flower bud differentiation to fruit set were sequentially analyzed in both types of shoots, over 2 years. More than half of the buds from long shoots aborted development and dropped before flowering. At anthesis, most of the remaining flowers showed underdeveloped pistils that failed to sustain pollen germination or pollen tube growth along the pistil. This unsuccessful development resulted in clear differences in fruit set between both types of branches. These results highlight that flower bud differentiation and development play an important role for fruit set and that developmental timing appears critical to reach anthesis with a fully developed pistil.     

Inter- and intra-floral heterogeneity of nectar production in Helleborus foetidus L. (Ranunculaceae)

Three southern Spanish populations of Helleborusfoetidus L. (Ranunculaceae) were sampled for nectar content in the absence of nectarivorous flower visitors. Nectar volume was measured in individual nectaries of flowers at the same stage in the anthesis cycle. Total nectar content per flower was extremely variable between plants within populations and between flowers within plants, but much less so between populations. Average sugar content per flower was roughly similar in the three populations sampled. High variances in nectar abundance occurred also among nectaries within the same flower. Heterogeneity in pollinator rewards thus occurs simultaneously at several spatial scales, namely between nectaries, between flowers and between plants. This implies a strong component of uncertainty to foraging pollinators, which may therefore tend to avoid Helleborus flowers.     

Pistil traits and flower fate in apricot (Prunus armeniaca)

Although pollination is essential for both seed and fruit set in most angiosperms, even after an adequate pollination, only a fraction of the flowers develop into fruits. The role played by floral traits on reproductive success is well known, but the possible influence of pistil traits has been overlooked, probably because of the difficulty of non-destructive pistil examination. The aim of this work was to examine the influence of several pistil traits on reproductive success in apricot ( Prunus armeniaca ). For this purpose, in a population of individually labelled flowers, the styles were cut off once the pollen tubes had reached the ovary but prior to the achievement of fertilisation. This approach allowed relating several morphological and physiological pistil parameters in the dissected styles and stigmas to the subsequent set or abscission of the corresponding ovary that remained in the plant. Under the same pollination conditions, the flowers that finally set a fruit show a larger stigmatic area and a higher number of pollen grains, pollen tubes growing along the style and xylem vessels surrounding the transmitting tissue than flowers that abscise before the establishment of fruit set. Furthermore, starch is present in the transmitting tissue of the style in all the flowers that develop into fruits but only in half of the flowers that abscise. The examined pistil traits established prior to fertilisation are related to flower fate, suggesting that the capacity of a flower to become a fruit could be preconditioned at anthesis.     

常春二乔玉兰春夏季开花节律及营养效应研究

为系统掌握常春二乔玉兰春夏季开花物候节律,探讨其与营养物质的关系,本研究以6年生常春二乔玉兰为试验材料,观测其年生长发育节律、春夏季开花物候特性以及茎段营养物质的含量变化。结果表明：（1）每年12月始至翌年2月下旬为常春二乔玉兰休眠期。2月下旬花芽膨大生长,并于3月开始春季开花,花期持续约20 d。4月进行营养生长,5月完成花芽分化。5月底部分花芽膨大并于6月开始开花,夏季花期持续约20 d。7~9月为未膨大花芽的发育滞缓期。此外,少量夏季开放的花的基部侧芽再次分化形成花芽。10~12月随着落叶的开始,树体逐渐进入休眠期。（2）常春二乔玉兰营养生长后分化的花芽能够花开两季。春季开花为先花后叶,开花率为100%,开花同步率较高,雌、雄蕊发育正常,为可育花。夏季开花为花叶同放,开花率约为30%,且开花同步率较低,开放的花内雌、雄蕊发育异常,为不育花。（3）春季开花期间可溶性糖和可溶性蛋白呈下降趋势,淀粉含量于开花后期下降;夏季开花期间可溶性糖和淀粉总体呈先降后升趋势,而可溶性蛋白总体呈下降趋势。综上所述,常春二乔玉兰春、夏季开花期内开花模式存在一定差异,其显著节律特征与营养物质含量变化有关,推测低水平的可溶性糖及高水平的淀粉和可溶性蛋白有利于春季开花的启动,而低水平的可溶性蛋白及高水平的可溶性糖和淀粉含量则有利于夏季开花的实现。     

Female flower and cupule structure in Balanopaceae,an enigmatic rosid family

The Balanopaceae, whose flowers were poorly known, have, in the past, been variously allocated to the Fagales, Euphorbiaceae, Salicales or other hamamelids and rosids (these groups being in Fagales, Malpighiales and Saxifragales, according to the Angiosperm Phylogeny Group). This paper attempts a clarification based on flower morphology. Female flowers and cupules were studied in Balanops vieillardii, young fruits in B. australiana. The cupules are simple involucres of bracts which are spirally arranged (according to a Fibonacci pattern) on the floral axis preceding the flower. They contrast with the complicated cupules of Fagaceae which consist of a condensed cymose ramification system of axes of several orders around the flower. Flowers appear later than most of the cupular bracts, in contrast to Fagaceae. In addition to a terminal flower there may be several smaller lateral flowers in the axil of cupular bracts, each surrounded by its own small cupule. The female flowers do not have a perianth. They consist of two to three large carpels. At anthesis, the ovary is completely septate; the syncarpous part (ovary and lower style) is completely symplicate. The carpels are free for most of their length, with the free parts once, twice or three times bifurcate, in contrast to simple in Fagales. The stigmatic surface covers the ventral side of each stigmatic branch and at the margins also spreads to the dorsal side. The stigma is wet and secretion appears holocrine. The two ovules per carpel are collateral and axile in early development. However, at anthesis they appear one above the other, because in one ovule the funicle greatly elongates. As the ovary elongates only above the placenta, the ovules appear basal at anthesis. The ovules are (weakly) crassinucellar, bitegmic (not unitegmic), anatropous, and intermediate between apotropous and epitropous (not apotropous). The ovules are mature at anthesis, in contrast to Fagales. In mature ovules the upper part of the nucellus disintegrates, and a weakly differentiated endothelium is present in the inner integument. The morphological results of this study support a position of Balanopaceae in Malpighiales, and not Fagales or other orders, and are thus in accordance with recent molecular results based on chloroplast rbcL sequences data. However, within Malpighiales, as opposed to molecular results, Balanopaceae agree more with Euphorbiaceae s.l. than with Dichapetalaceae/Trigoniaceae and Chrysobalanaceae/Euphroniaceae.     

Nectary structure and nectar presentation in Aloe castanea and A. greatheadii var. davyana (Asphodelaceae)

This paper deals with the nectary structure and nectar presentation of two species belonging to different sections of the genus Aloe: A. castanea (Anguialoe) and A. greatheadii var. davyana (Pictae). The development of the nectary was studied by means of bright field and fluorescence light microscopy and scanning electron microscopy (SEM) in three flower stages (young, intermediate, old). Both species have septal nectaries. In A. castanea, a subsidiary tissue, not present in A. greatheadii var. davyana, was found beneath the nectary epithelium. This tissue accumulated starch that was hydrolyzed during secretion. Starch was slightly accumulated around the nectary in A. greatheadii var. davyana. The distribution of chlorophyll in the ovary was also different in the two species. These anatomical differences are not, however, correlated with greater nectar production in A. castanea. In this species, the nectary seems to degenerate after secretion, while in A. greatheadii var. davyana no sign of degeneration was observed. Differences in nectar presentation among the two species may account for different pollinators visiting their flowers.     

Fruit Abscission in Cowpea, Vigna unguiculata (L.) Walp.: II. QUANTITATIVE ESTIMATIONS OF TOTAL NUCLEIC ACIDS IN OVARIES OF PERSISTING AND ABSCISSING FLOWERS

The fresh weights and quantities of total nucleic acids (RNAand DNA) in the ovaries of abscissing flowers and persistingflowers were estimated at intervals. Starting from 48 h prior to anthesis, particularly during the24 h immediately preceding it, large differences were observed:ovaries of abscissing flowers were much lighter and accumulatedmuch less nucleic acid than those of persisting flowers. Forinstance, at anthesis the ovaries of persisting flowers (atraceme 1, in acropetal order) were twice as heavy, and containedtwice as much DNA and one-and-a-half times as much RNA as theovaries of abscissing flowers (at raceme 3). These differenceswere further maintained from after the flowers had opened untileventual shedding of the raceme 3 flowers. The results provided clear evidence of the very basic retardationexperienced by the abscissing flower before and after opening.