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.     

THE GLYCOCALYX AND INITIATION OF EXINE SPINULES ON MICROSPORES OF CANNA

Spinules of Carina generalis pollen are initiated within a tridimensional network during the microspore tetrad period. The network is stained selectively with the hydrazide-silver proteinate method of Thiéry following periodate oxidation and by phosphotungstic acid at low pH, demonstrating the presence of polyanions. Protein is indicated as a component of the network by positive staining with PTA in acetone. These results suggest the presence of polysaccharides and proteins, possibly as mucopolysaccharides or glycoproteins. The network may be considered as a part of the glycocalyx because of its composition and association with the plasma membrane. Sporopollenin accumulates on the tridimensional network or in meshes of the net. The beaded fine structure of spinules resists the acetolysis mixture of Erdtman. Our results imply that the plasma membrane and its glycocalyx are part of the system which mediates genetic expression of exine form. The implication is compatible with formation of specific exines on all pollen grains of a plant and on aborted microspores, diminutive spores with depauperate chromosome complements, and enucleate bodies of cytoplasm resulting from meiotic abnormalities.     

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。     

白蚁初期群体的形成及其行为的观察

家白蚁Coptotermes formosanus Skiraki和黑翅土白蚁Odontotermes formosanus(Skiraki)在我国是分布广,为害大的二种重要害虫。家白蚁危害建筑材料、房屋、橡胶、塑料、地下电缆、尼龙等有机合成材料,部分金属和农林作物,危害涉及到国民经济各个部门;而黑翅土白蚁严重地为害堤坝,我国南方各省水库堤坝为害率达53—92％,严重地区发生漏水的占20％,为害农林作物亦很严重。对它们的生物学和生态学特性及防治方法,国内外已有不少研究报道,但对它的生殖行为、孵化、脱皮习性,目前尚少有较系统的资料。因此,本试验试图通过家白蚁和黑翅土白蚁初期群体的形成,进行较详细的观察,为深入探讨白蚁的生物学和生态学特性提供真实依据。     

ORGAN INITIATION AND DEVELOPMENT OF INFLORESCENCES AND FLOWERS OF ACACIA BAILEYANA

Inflorescence and floral ontogeny are described in the mimosoid Acacia baileyana F. Muell., using scanning electron microscopy and light microscopy. The panicle includes first-order and second-order inflorescences. The first-order inflorescence meristem produces first-order bracts in acropetal order; these bracts each subtend a second-order inflorescence meristem, commonly called a head. Each second-order inflorescence meristem initiates an acropetally sequential series of second-order bracts. After all bracts are formed, their subtended floral meristems are initiated synchronously. The sepals and petals of the radially symmetrical flowers are arranged in alternating pentamerous whorls. There are 30–40 stamens and a unicarpellate gynoecium. In most flowers, the sepals are initiated helically, with the first-formed sepal varying in position. Petal primordia are initiated simultaneously, alternate to the sepals. Three to five individual stamen primordia are initiated in each of five altemipetalous sectorial clusters. Additional stamen primordia are initiated between adjacent clusters, followed by other stamens initiated basipetally as well as centripetally. The apical configuration shifts from a tunica-corpus cellular arrangement before organogenesis to a mantle-core arrangement at sepal initiation. All floral organs are initiated by periclinal divisions of the subsurface mantle cells. The receptacle expands radially by numerous anticlinal divisions in the mantle at the summit, concurrently with proliferation of stamen primordia. The carpel primordium develops in terminal position by conversion of the floral apex.     

吗啡和纳洛酮对豚鼠离体胆囊肌条活动的作用

5种浓度的吗啡对胆囊肌条的自动节律性收缩,均有明显加强作用。阿片受体拮抗剂——纳洛酮可阻断和翻转吗啡对胆囊肌条的作用,说明豚鼠的胆囊壁有阿片受体。乙酰胆碱显著地加强胆囊肌条的收缩,此效应可被阿托品阻断,而且阿托品也使吗啡对胆囊肌条的作用明显减弱。异丙肾上腺素和去甲肾上腺素分别抑制和加强胆囊肌条的运动,前者的效应可被心得宁阻断,后者则被酚妥拉明阻断,但两者的效应均不受纳洛酮的影响。而心得宁和酚妥拉明不影响吗啡对胆囊肌条的作用。本实验似能表明,吗啡对胆囊肌条运动的调节是通过阿片受体而起作用的。但吗啡对胆囊肌条的作用与肾上腺素能α和β受体无关。     

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.     

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.     

A SCANNING ELECTRON MICROSCOPIC STUDY ON THE INITIATION AND DEVELOPMENT OF FLORAL ORGANS OF BRASSICA NAPUS (CV. WESTAR)

The initiation and development of the floral organs of Brassica napus L. (cv. Westar) were examined using the scanning electron microscope. After transition of the vegetative apex into an inflorescence apex, flower primordia were initiated in a helical phyllotactic pattern. The sequence of initiation of the floral organs in a flower bud was that of sepals, stamens, petals and gynoecium. Of the four sepal primordia, the abaxial was initiated first, followed by the two lateral and finally the adaxial primordium. The four long stamens were initiated simultaneously in positions alternating with the sepals. The two short stamens were initiated basipetal to and outside the long stamens, and opposite the lateral sepals. The petals arose on either side of the two short stamens and the gynoecium was produced from the remainder of the apex. During development, the sepal primordia curved sharply at the tips and tightly enclosed the other organs. Stamen primordia developed tetralobed anthers at an early stage while filament elongation occurred just prior to anthesis. A unique pattern of bulbous cells was present on the abaxial surface of the anther. Growth of petal primordia lagged relative to the other floral organs but expansion was rapid prior to anthesis. The gynoecium primordium was characterized by an invagination early in development. At maturity, there was differentiation of a papillate stigma, an elongated style and a long ovary marked externally by sutures and divided internally by a septum. Distinct patterns of cuticular thickenings were observed on the abaxial and adaxial surfaces of the petals and stamens and on the surface of the style. The patterns were less obvious on the sepals and ovary. Stomata were present on both surfaces of the mature sepals, on the style and restricted areas on the abaxial surface of the anthers and nectaries but were absent from the petals, the adaxial surface of the stamens and the ovary. No hairs were present on any of the floral organs.