MORPHOLOGY OF MARSILEA VESTITA. I. ONTOGENY AND MORPHOLOGY OF THE SUBMERGED AND LAND FORMS OF THE JUVENILE LEAVES

During their ontogeny, the primordia of the juvenile leaves of Marsilea plants in sterile culture develop 1, 2 or 4 marginal meristems, and these, in turn, contribute cells to the young leaf by anti- and periclinal cell divisions. The final leaves are unifid, bifid, or quadrifid, depending on how many marginal meristems develop, and this is determined early in the ontogeny of the leaf. The mechanism which determines whether or not a marginal meristem develops may fluctuate, as shown by the existence of trifid leaves. Two forms of juvenile leaves are produced, those in a liquid medium, which in many respects resemble the adult quadrifid submerged leaves, and those on a solid medium, which in many respects resemble the adult land leaves.     

THE DEVELOPMENT OF THE SPOROCARP OF MARSILEA VESTITA

The tissues of the sporocarp of Marsilea vestita undergo profound changes during development. Early in development, the cells of the peripheral tissues, epidermis, hypodermis and layers of the transitional zone between the hypodermis and more internal tissues contain prominent vacuolar bodies. As development proceeds, these vacuolar bodies disappear. Prominent amyloplasts are found only in the guard cells and in the cells of the transitional zone. Later in development the cells of the hypodermis divide periclinally forming two layers which differentiate as macrosclereids. The cells of the outermost layer of the transitional zone differentiate as osteosclereids. Internally, the cells of the sorophore accumulate large amounts of mucilage in the central vacuoles. The peripheral cytoplasm ultimately degenerates leaving just hygroscopic mucilage. The mucilage carbohydrate contains the sugars, rhamnose and arabinose. In the young sorus, only the spore mother cells and the cells of the indusium contain amyloplasts. By the time of meiosis, there is a massive accumulation of starch in the receptacle, stalk and jacket but not in the tapetum of the sporangia. Late in development, the starch disappears and the mega- and microspores become coated with carbohydrate.     

THE HYDRATED MEGASPORE OF MARSILEA VESTITA

The megaspore of Marsilea has an exospore composed of several layers and is contained within the original megasporangial wall (making it technically a megasporangium). Upon contact with water there is an almost explosive unrolling of the megasporangial wall and expansion of the spore wall layers into a complex structure, part of which has not been previously described. The dynamics of the hydration process and the resultant structures are described.     

KINETIN MODIFICATION OF SPORELING ONTOGENY IN MARSILEA VESTITA

Laetsch , W. M., and Winslow R. Briggs . (Stanford U., Stanford, Calif.) Kinetin modification of sporeling ontogeny in Marsilea vestita. Amer. Jour. Bot. 48(5): 369–377. Illus. 1961.—Sporelings of the fern, Marsilea vestita Hook. and Grev., were cultured aseptically with a wide concentration range of kinetin. The elongation of the primary and all succeeding roots was significantly inhibited by concentrations as low as 0.3 γ/l., and was almost completely inhibited at concentrations above 30 γ/l. Root inhibition by kinetin was a result of decreased cell division and was not influenced by the amount of available carbon in the medium. The primary leaves also were inhibited by kinetin, but only by higher concentrations. The relative numbers of organs present were altered by intermediate concentrations, with a rise in the number of roots per plant, and a corresponding decrease in the number of leaves. Sporelings maintained in these kinetin concentrations for long periods developed abnormal leaves and roots. The shoot apex lost its organization in higher concentrations and proliferated into callus. The histology of the callus is discussed. The kinetin effects were independent of light conditions. Various other growth-active compounds were studied in combinations with each other and with kinetin for their effects upon sporelings. Interactions between these compounds were not apparent, and they neither substituted for nor modified the effects of kinetin. The use of kinetin as a tool in morphogenetic study is discussed.     

MITOTIC ACTIVITY IN THE ROOT APEX OF THE WATER FERN MARSILEA VESTITA HOOK. AND GREV.

Roots of Marsilea vestita ranging from 1–120 mm in length, as well as root primordia, were analyzed to determine mitotic activity and ploidy levels in the apical cell, five well-defined regions of the root proper, and two regions in the root cap. The mitotic index of the apical cell tended to be above the overall mean mitotic index for the entire apical meristem. No diurnal rhythm in mitotic index was apparent. The cell-cycle duration of the apical cell ranged from 12.1–25.2 hr, that of other regions of the root from 16.1–41.5 hr. There was no indication of polyploidy in any part of the apical meristem except in a few procambial cells. Thus, the results support the classical concept that the apical cell is the ultimate source of cells in the root.     

EFFECTS OF CARBON DIOXIDE ON THE GROWTH AND MORPHOGENESIS OF MARSILEA

Increased concentrations of CO₂ in air (1–50%) cause young plants of Marsilea vestita to exhibit many characteristics of the water form when they are grown on a solid substrate under sterile conditions. Thus these plants have longer internodes, shorter petioles, more rectangular-shaped epidermal cells and fewer stomata on the lower leaf epidermis than controls grown in 0.03% CO₂. Over a 2-week period, dry weight increase is considerably greater in 12.5% and 25% CO₂ than in 0.03% CO₂. Fifty percent CO₂ is inhibitory to growth. CO₂-enriched air has the same morphogenetic effect when supplied in the light or the dark. Possible explanations for this effect are discussed.     

OBSERVATIONS ON THE MORPHOLOGY AND PHYSIOLOGY OF MARSILEA SPERM

The multiciliated sperm of the water fern Marsilea vestita was examined with a view to establishing its suitability as an experimental subject. Time-course experiments revealed spermatid development to be temperature dependent. Sterile techniques were devised for observation of sperm on both a population and an individual basis. Sperm discharge, active and senescing sperm were examined by phase-contrast microscopy. A regular pattern of senescence was ascertained. This included vacuolation of the cytoplasmic vesicle, loss of motility, and ultimate loss of the helical structure of the sperm coil. Sperm life spans were recorded using motility and O₂ uptake as criteria. Sperm populations are active 3–3½ hr at ambient temperature (22–25 C). Individual sperm are active less than 1 hr. Sperm suspensions show a decline in O₂ uptake which parallels the loss of motility. Various constituents affecting the life span were investigated. A twofold prolongation of the sperm life span occurred in the presence of 0.1 m sucrose. An ultrastructural examination of the mature sperm was made to aid in assessing its metabolic potential. The sperm shows little ultrastructural differentiation. The cytoplasmic vesicle is predominantly composed of starch-containing plastids. The main structural components of the sperm coil are a continuous mitochondrial band, an elongate nucleus, and a series of microtubules which separate the basal bodies from the nucleus and mitochondrion. A comparison of ultrastructural features common to Pteridium and Marsilea was made and factors affecting senescence discussed.     

COMPARATIVE MORPHOGENESIS OF THE DIMORPHIC LEAVES OF CYAMOPSIS TETRAGONOLOBA

Cyamopsis tetragonoloba, guar, produces two leaf forms: a simple leaf and a trifoliate leaf. The steps in the development of each of these forms have been investigated in an attempt to determine the precise point at which the leaf primordium becomes destined to produce one or the other characteristic leaf shapes. Up to 140 μ in length the leaf primordia are morphologically indistinguishable. If a simple leaf is to be formed the marginal meristem remains continuous and initiates only lamina. If a trifoliate leaf is to be formed the continuity of the marginal meristem is interrupted by a group of “pocketal” cells dividing it into an upper lamina meristem and a basal leaflet buttress.     

红色角毛虫的形态学和形态发生过程的研究

观察并描述了上海采集到的红色角毛虫的形态结构和形态发生过程。发现形态发生时虫体分别于前、后两个区域发生前、后两个口围带原基,并且由同一个体分裂而成的前,后两个仔虫内,额、腹、横棘毛和缘棘毛的分化并不完全相同,以至造成两个仔虫上棘毛的数目和缘棘毛的列数有明显差异。根据红色角毛虫的形态结构及其形态发生中的一些不够稳定的特点,推测它可能是一种还处于分化中的腹毛类纤毛虫。