ORGAN INITIATION AND THE DEVELOPMENT OF UNISEXUAL FLOWERS IN THE TASSEL AND EAR OF ZEA MAYS

The development of the unisexual male and female flowers of Zea mays from bisexual initials in both tassels and ears has been reinvestigated with SEM and TEM. The early stages of spikelet branch primordia, spikelet initiation, and early flower development are similar in both flowers, though differences in rates of growth of glumes, lemmas, and palea were detected. In both tassel and ear flowers, a pair of stamens arises opposite the lemmas and a third stamen initiates later at right angles to the first pair but from a point on the meristem below its insertion. Gynoecia develop on both tassel and ear flowers first as a ridge which overgrows the apical meristem giving rise to the stylar canal and the elongate silk. Male flowers arise in the tassel through selective vacuolation and abortion of the cells of the early gynoecium. The single female flower in each ear spikelet arises through the vacuolation and abortion of stamens in the upper flower and the repression of growth of and the eventual regression of the lower flower in each spikelet. The significance of these selective organ abortions for practical applications is discussed.     

UNIDIRECTIONAL ORGAN INITIATION IN LEGUMINOUS FLOWERS

The order of initiation of floral organs is compared in several legumes. In Bauhinia fassoglensis, a caesalpinioid, the sepals are initiated helically, with the first one forming abaxially. In Genista tinctoria and Lupinus affinis (both papilionoids) the sepals are initiated unidirectionally, with the first forming on the abaxial side of the floral apex and subsequent sepals initiating laterally and then adaxially. All three taxa show unidirectional order of initiation for petals, first-whorl stamens, and second-whorl stamens. In each whorl, the first member or members form on the abaxial side, next to the subtending bract, then the lateral ones, and lastly the member(s) on the adaxial side, next to the axis. In Lupinus and Genista there are overlaps in time of initiation between organs in different whorls; for instance, the first stamens begin initiating before the last petals appear. Size differences among members of a whorl are evident in early stages, but may disappear after organogeny ceases, when the members become equal in size in each whorl. This precocious onset of dorsiventrality in floral development is viewed as a specialized feature.     

OVERLAPPING ORGAN INITIATION AND COMMON PRIMORDIA IN FLOWERS OF PISUM SATIVUM (LEGUMINOSAE: PAPILIONOIDEAE)

The floral ontogeny of Pisum sativum shows a vertical order of succession of sepals, petals plus carpel, antesepalous stamens, and antepetalous stamens. Within each whorl, unidirectional order is followed among the organs, beginning on the abaxial side of the flower, as in most papilionoids. Unusual features include the four common primordia which precede initiation of discrete petal and antesepalous stamen primordia, and the marked overlap of organ initiations between whorls which are usually separately initiated. The stamens arise in free condition, then become diadelphous by intercalary growth at the base of nine stamens, and finally become pseudomonadelphous by surface fusion between the vexillary stamen filament and the adjacent edges of the filament tube. The early initiation of the carpel is not unique among papilionoids, but is somewhat unusual.     

PHOTORESPONSES OF PHYCOMYCES BLAKESLEEANUS: INITIATION AND DEVELOPMENT OF SPORANGIOPHORE PRIMORDIA

Phycomyces blakesleeanus (Burgeff) produces both giant and dwarf sporangiophores from superficial and submerged hyphae. The morphogenesis of submerged primordia has been studied in cultures grown in petri dishes on a defined nitrogen-poor medium at low temperature under varied conditions of illumination. The primordia of dwarf and giant sporangiophores differed markedly in size, morphology, tropistic behavior, developmental plasticity, photosensitivity, and conditions required for initiation. Dwarf primordia, abundant only in dark-grown cultures, began as hyphal thickenings that later developed characteristic ramifications not seen in giant primordia. The formation of dwarf primordia was correlated spatially and temporally with termination of mycelial expansion near the rim of the dish and in local regions elsewhere. Illumination strongly suppressed the ramification process in existing primordia but did not prevent the maturation of dwarf sporangiophores that had already emerged from the nutrient surface. Giant primordia were prominent only in illuminated cultures. With continuous light from the time of inoculation, giant sporangiophores and giant primordia were found chiefly in midregions of the dish. If illumination was delayed until dwarfs had begun to form near the rim of the dish, the giant primordia were also concentrated near the rim. In that case about half of the giants were formed by conversion of a small fraction of the existing dwarf primordia and the rest were formed de novo from vegetative hyphae.     

ANATOMY AND ASPECTS OF DEVELOPMENT OF THE STAMINATE INFLORESCENCES AND FLORETS OF SEVEN SPECIES OF ALLOCASUARINA (CASUARINACEAE)

The morphology, ontogeny, and vascular anatomy of the staminate inflorescences and florets of seven species of Allocasuarina are described. The generally terminal but open-ended inflorescences occur on monoecious or staminate dioecious trees and consist of whorls of bracts, each subtending a sessile axillary floret. Each floret consists of one terminal stamen with a bilobed, tetrasporangiate anther enclosed typically by cuculliform appendages, commonly considered bracteoles, an inner median pair and an outer lateral pair. The mature stamen is exerted, the anther is basifixed and is extrorsely dehiscent. In early development of a male inflorescence very little internodal elongation occurs and enclosing cataphylls appear. The inflorescence apex is a low dome with a uniseriate tunica and a small group of central corpus cells. Bract primordia are initiated by periclinal divisions of C₁ followed by further divisions of the corpus and anticlinal divisions in the tunica. The bracts are epinastic and become gamophyllous except apically by cell divisions in both sides of each primordium. Stomata are restricted to the axis furrows and the abaxial tips of the bracts. The axillary florets arise in acropetal succession initiated by periclinal divisions in C₁ accompanied by anticlinal divisions in the tunica. The lateral floral appendages are also initiated by C₁ followed by anticlinal divisions in the tunica. They become adnate basally later with the subtending bract. The median sterile appendages are initiated in a manner similar to the initiation of the outer appendages. The stamen is initiated by divisions in the outer layers of the corpus and in the tunica, and then develops first by apical growth followed by intercalary growth. The vascular system of the inflorescence is identical to that of the vegetative stem. Each floret is supplied by a single bundle that has its source in a branch from each of the two traces supplying a bract. Six bundles arise from the floral bundle; four of these terminate in the base of the stamen and two form an amphicribal bundle that supplies the anther. Pollen is binucleate, 3- to 7-porate. The exine is tegillate.     

INITIATION AND DEVELOPMENT OF ROOT NODULES OF CASUARINA (CASUARINACEAE)

Roots of seedlings of the “beefwood” tree, Casuarina cunninghamiana Miq. grown in nitrogen-free nutrient solution were inoculated with a suspension prepared from crashed root nodules taken from mature plants. Marked deformation of root hairs was evident but no infection threads were observed in root hairs. The mode of infection remains undetermined. Root nodules were initiated within three weeks and thereafter numerous upward-growing nodule roots developed from each nodule. Nodules in this symbiotic nitrogen-fixing plant resulted from an infection caused by an unidentified actinomycete-like soil microorganism. Anatomical analysis of nodule formation showed that nodules are the result of repeated endogenous lateral root initiations, one placed upon another in a complexly branched and truncated root system. The endophyte-infected cortical tissues derived from successive root primordia form the swollen nodular mass. Nodule roots develop from nodule lobes after escaping from the initial inhibitory effects of the endophyte. Included is a discussion of the anatomical similarities between nodules of Casuarina which produce nodule roots and those of Alnus which form coralloid nodules usually lacking nodule roots.     

DEVELOPMENT OF TASSEL SEED 2 INFLORESCENCES IN MAIZE

The normal pattern of maize floral development of staminate florets on the terminal inflorescence (tassel) and pistillate florets on the lateral inflorescences (ears) is disrupted by the recessive mutation tassel seed 2. Tassel seed 2 mutant plants develop pistillate florets instead of staminate florets in the tassel. In addition, the ears of tassel seed 2 plants display irregular rowing of kernels due to the development of the normally suppressed lower floret of each spikelet. The morphology of tassel and ear florets of the recessive maize mutant tassel seed 2 has been compared to those of wild-type maize through development. We have identified the earliest stages at which morphological signs of sex differentiation are evident. We find that sex determination occurs during the same stage on tassel and ear development. Early postsex determination morphology of florets in wild-type ears and in tassel seed 2 tassels and ears is identical.     

DEVELOPMENT AND VASCULATURE OF THE FLOWERS OF LOPHOTOCARPUS CALYCINUS AND SAGITTARIA LATIFOLIA (ALISMACEAE)

The development of the bisexual flower of Lophotocarpus calycinus and of the unisexual flowers of Sagittaria latifolia has been observed. In all eases floral organs arise in acropetal succession. In L. calycinus, after initiation of the perianth, the first whorl of stamens to form consists of six stamens and is ordinarily followed by two alternating whorls of six stamens each. The very numerous carpels arc initiated spirally. In the male flower of S. latifolia the androecium develops in spiral order. A few rudimentary carpels appear near the floral apex after initiation of the stamens. There are no staminodia. The female flower has a similar developmental pattern to that of Lophotocarpus except that a prominent residual floral apex is left bare of carpels. The vascular system in all flowers is semiopen, with vascular bundles passing to the floral organs in a pattern unrelated to the relative positions of those organs. The androecia of these two taxa are similar to those of some Butomaceae and relationships based on ontogeny and morphology are suggested. The gynoecia are meristically less specialized but morphologically more specialized than the gynoecia of Butomaceae.     

INITIATION AND DEVELOPMENT OF INFLORESCENCE AND FLOWER IN ANEMOPSIS CALIFORNICA (SAURURACEAE)

All flowers of Anemopsis californica, the most specialized taxon of the family Saururaceae, are initiated as individual primordia subtended by previously initiated bracts, in contrast to the common-primordium initiation of all flowers of Saururus cernuus and of most flowers of Houttuynia cordata. Floral symmetry is bilateral and zygomorphic, and the sequence of initiation among floral parts is paired or whorled. In A. californica, the six stamens arise as three common primordia, each of which later bifurcates to form a pair. The three common primordia occupy sites corresponding to the positions of the three stamens in H. cordata flowers. In Anemopsis, the filaments of each pair are connate. Each stamen pair is vascularized by a single bifurcating vascular bundle. The three carpels per flower are usually initiated simultaneously although there may be some variation. Adnation between stamens and carpels results from zonal growth. Downward extension of the locule, and proliferation and expansion of receptacular tissue and inflorescence cortical tissue around the locule below the bases of the carpels produce the inferior ovary. The inflorescence terminates its activity as a flattened apical residuum, surrounded by bracts subtending reduced flowers most of which have stamens only.     

大叶相思(Acacia auriculae formis)和马占相思(Acacia mangium)固氮量的研究

木本豆科植物固氮量的研究在国外已受到重视,其固氮量为7—500公斤/公顷·年,因植物种类及其所处的环境条件而各有不同,在国内研究木本豆科植物固氮活性的报道较多,但固氮量的研究报告却少见,为此我们对大叶相思和马占相思的固氮量进行了试探性的调查研究。     

Flowering in Xanthium strumarium: INITIATION AND DEVELOPMENT OF FEMALE INFLORESCENCE AND SEX EXPRESSION

Vegetative plants of Xanthium strumarium L. grown in long days were induced to flower by exposure to one or several 16-hour dark periods. The distribution of male and female inflorescences on the flowering shoot was described, and a scoring system was designed to assess the development of the female inflorescences. The time of movement of the floral stimulus out of the induced leaf and the timing of action of high temperature were shown to be similar for both the apical male and lateral female inflorescences.     

INITIATION AND DEVELOPMENT OF SHOOT-BUDS FROM PROTONEMATA IN THE MOSS PHYSCOMITRIUM TURBINATUM

Moss protonemata of Physcomitrium turbinatum were grown on mineral nutrient agar in culture tubes under various controlled conditions. By use of the described system individual cells of the protonema were discernible in situ and buds could be detected at the one-cell stage (initiation) and observed throughout their development. Buds normally arose by differentiation of a lateral filament near the apex of a growing caulonemal (heterotrichous) strand. Other modes of origin were erratic. From various other observations we conclude that the most pertinent morphological assays in studies of bud differentiation are growth of single caulonemal strands and the time they require to initiate a bud. A time course for bud development from the one-cell stage through the stage of leaf expansion is presented. At 26 C, 2 days elapse between these stages. From the time course, the time of bud initiation could be estimated with a probable accuracy of ±2 hr with only daily observations.     

油松树脂道的发生和发育研究

关于松科植物的树脂道,以往都认为是以裂生方式发生。本文通过对油松各类器官的发育解剖学研究,发现其各类器官中树脂道的结构,发生和发育方式并不完全一致,并对产生这些差异的原因进行了分析和讨论。     

BASIDIOSPORE INITIATION AND EARLY DEVELOPMENT IN COPRINUS CINEREUS

Early basidiospore development in Coprinus cinereus has been divided into four stages: 1) inception, 2) asymmetric growth, 3) equal enlargement, 4) elongation, all based on changes in spore size and shape, wall layering, and cytoplasm. The hilar appendix body formed on the adaxial side of the stage 1 basidiospore, persisted through all stages studied, and predicted the site of the hilar appendix. The hilar appendix formed in stage 2 by modification of certain wall layers. A band of peripheral endoplasmic reticulum covered an average of 38 % of the lower spore wall in stage 3 and was oriented around the axis of growth. Stage 4 was initiated by a break in wall layer 3 at the spore apex and the disappearance of the peripheral endoplasmic reticulum. A pore cap formed on the spore apex during spore elongation. The spore wall consisted at first of three layers and became six layered by deposition of layers between two of the initial layers. Cytoplasmic changes associated with spore growth included presence of small vesicles at stage 1 and larger Golgi vesicles later, absence of mitochondria and probable Golgi cisternae from the spore until stage 3, and presence of a zone nearly free of ribosomes and organelles under the spore apex in stage 4. Functions of the hilar appendix body, peripheral endoplasmic reticulum and the different wall layers in control of spore shape are discussed.