摘要:

SUMMARYThe dinophysoid dinoflagellates (to whichOrnithocercusbelongs) achieve growth both by increase in size of individual wall elements and, during rapid lateral expansion associated with cell division, by the formation of a semimeridional band of material termed the megacytic zone (MZ). The MZ maintains mother cell wall integrity during complete cytokinesis of the cell body and enclosure with new wall elements. The lists, extensive wing‐like extensions of the wall, can only be reformed after dissolution of the MZ. Beginning near the ventral region (which is the last region of the wall to be duplicated), the MZ dislocates and its material is apparently resorbed. The last region of attachment is invariably dorsal and in several, but not all species, the daughter cells may remain attached during early list formation by a special remnant of the MZ, termed here the dorsal megacytic bridge (DMB). After full separation of daughter cells remnants of the DMB persist for an unknown but presumably short period.The topography of this process, involving radical ontogenetic alterations in the appearance of the daughter cells and some wall surfaces, is illustrated here by the scanning electron microscope. In addition 2 aberrant types of division are shown, one of which results in a double individual, termed a geminoi

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1973.00001.x

出版商:Blackwell Science Inc    

年代:1973

数据来源: WILEY

ISSN:0022-3646    

DOI:10.1111/j.1529-8817.1973.tb02435.x

出版商:Blackwell Science Inc    

年代:1973

数据来源: WILEY

摘要:

SUMMARYPseudotetracystis terrestris gen. et sp. nov., a member of the Chlorosarcinaceae, was isolated into axenic culture from dry surface soil collected near Texon in Reagan County, Texas. The characteristics of this presently monotypic genus include vegetative cells with a parietal chloroplast, a single pyrenoid, and polymorphic motile cells which are of theProtosiphon‐type (naked with 2 equal flagella); P. terrestrisis the type species. Vegetative cell division (desmoschisis) forms diads and tetrahedral or planar tetrads, sometimes aggregated in transitory complexes. Reproduction is by the polymorphic motile cells which may function either as gametes to form zygotes which develop without dormancy directly into vegetative cells, or they may function as zoospores and develop directly into vegetative cells without unio

ISSN:0022-3646    

DOI:10.1111/j.1529-8817.1973.tb04056.x

出版商:Blackwell Science Inc    

年代:1973

数据来源: WILEY

摘要:

SUMMARYThe Ultrastructure ofMicrothamnionzoospores is described (exclusive of the finer details of the flagellar apparatus). The zoospores have a typical chlorophycean morphology but, in addition, many unique features. The chloroplasts contain starch but no pyrenoid. Thylakoids may run from one edge of the chloroplast to the other and usually anastomose into 2‐ to 8‐membered stacks. The internal morphology is highly polarized and characterized by an intimate proximity and constant spacing between many organelle membranes. All the organelles are asymmetrically distributed within the cell in a precise manner. The anterior region of the zoospore is attenuated into a neck which contains a single, massive mitochondrion. A fibrous rhizoplast lies beside the mitochondrion and appears to connect the flagellar apparatus directly with the outer membrane of the nuclear envelope. In addition, this outer membrane is extended over a distance of several microns to eventually lie in close proximity to the basal bodies. Oil vacuoles and lipid bodies are restricted to the posterior end of the zoosp

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1973.00015.x

出版商:Blackwell Science Inc    

年代:1973

数据来源: WILEY

摘要:

SUMMARYBoth tetrasporangia and dormant apical cells of short vegetative filaments of the marine red algaPtilota hypnoideshave been examined by electron microscopy. Various cytoplasmic inclusions readily distinguish the vegetative apical cells from the reproductive apical cells which become tetrasporangial mother cells. The transformation of tetrasporangial mother cells into mature tetrasporangia involves a series of cytoplasmic changes which can be correlated with specific changes in the investing wall layers. The extracellular changes provide the basic criteria for the division of tetrasporogenesis into 3 successive stages. The ultrastructure of each stage is described and discussed in relation to the current knowledge of red algal cytology. In addition, a possible mechanism for the liberation of spores and gametes of red algae is proposed.

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1973.00029.x

出版商:Blackwell Science Inc    

年代:1973

数据来源: WILEY

摘要:

SUMMARYThe diatomCocconeis scutellum(Meunier) colonizes the surface of young plants emerging from the mud in the spring and the usually emersed plant tips as they are knocked over and become immersed in the fall to form a virtually unialgal mat. Broken frustules and detritus adhere to form a crust which then becomes colonized nonselectively by a variety of microorganisms. Removal of the crust shows that the original “cobblestone” surface of the eelgrass is obscured with a layer of deformed cells ofC. scutellumwhich appears to be impressed into the epithel

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1973.00046.x

出版商:Blackwell Science Inc    

年代:1973

数据来源: WILEY

摘要:

SUMMARYA detailed fine structural study of the nondividing vegetative cell of the centric diatomMelosira variansreveals peripheral organization of cytoplasm and organelles around a central vacuole. Polarity of the cell is such that the nucleus is found at the valve face of the epitheca. The unusual shape of the nucleus and its associated microtubular system and polar body are thought to relate to the migration of the nucleus during other phases of cell growth. Unusual discontinuities of the plastid lamellae are reported and the significance of the periplastid reticulum is discussed. Possible roles for the cytoplasmic vesicles and the membrane system in the cell are also considered.

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1973.00050.x

出版商:Blackwell Science Inc    

年代:1973

数据来源: WILEY

摘要:

SUMMARYEvents prior to, during, and immediately following plasmogamy have been investigated inOedogonium cardiacumusing combined techniques of light and electron microscopy. Maturation of the oogonium involves the formation of an oogonial pore and the differentiation of the single egg from the larger oogonial protoplast from which it is formed. The fine structure of the sperm cell at the time of plasmogamy is described as well as the nature of its entrance into the oogonium. Cinematographic films were used to analyze the movements of the spermatozoids prior to plasmogamy and, similarly, 26 complete acts of gametic fusion were recorded and analyzed. Prior to plasmogamy the flagella‐bearing anterior extremity of the spermatozoid typically becomes elongate and is thereafter capable of flexible movements and rapid changes in shape which appear more or less independent of the rest of the cell. The sperm cell always makes initial contact with the egg surface by means of this agile, proboscis‐like, anterior end. Contact results through a combination of thrusting movements of the entire sperm cell and rapid, lateral sweeping movements of its flagellated anterior extremity against the egg surface. Gametic fusion is initiated with violent, vibrational movements of the sperm cell accompanied by loss of its flagella. Apparent fusion of the gamete membranes unites their protoplasts by a narrow cytoplasmic bridge which gradually increases in size as the sperm cell cytoplasm flows into the egg. An average time of 30.5 sec was required for complete fusion as determined from 25 typical sequences of plasmogamy recorded cinematographically. Fusion occurs even more rapidly when diploid oogonia are substituted for daploid oogonia. The entire sperm cell, with the exception of the flagella, fuses with the egg during plasmogamy. The dissimilar gamete nuclei are clearly distinguished ultrastructurally in the binucleate fusion cell. Concentrations of sperm cell mitochondria and remains of the flagellar apparatus (but no flagella) are readily recognized in the fusion cell. The fate of these and other cytoplasmic constituents of the sperm cell is discussed. Immediately after plasmogamy, and prior to karyogamy, a thin, finely fibrous layer is formed us an investment exterior to the fusion cell. Karyogamy follows shortly after plasmogamy, and both events may take place within 15 min after mixing eggs and spermatozo

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1973.00062.x

出版商:Blackwell Science Inc    

年代:1973

数据来源: WILEY

摘要:

SUMMARYThe differentiation of male gametes of the marine red algaPtilota densawas studied by electron microscopy. Mature primary spermatangia are enveloped by a single cell wall and possess a clearly polar subcellular organization. The nucleus is situated apical to large, striated, fibrous vacuoles which are apparently formed by the repeated fusion of dictyosome vesicles. The transformation and liberation of spermatia from spermatangia involve both the secretion of the fibrous vacuoles at the base of the cell and the subsequent rupturing of the spermatangial cell wall. Liberated spermatia are coated with a thin mucilage layer and contain numerous small vesicles and several mitochondria and dictyosomes. The nucleus is cup‐shaped and generally lacks a limiting envelope. These findings are discussed in relation to other light and electron microscopic studies of differentiating spermatangia in red alga

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1973.00085.x

出版商:Blackwell Science Inc    

年代:1973

数据来源: WILEY

摘要:

SUMMARYLight and electron microscopy indicate thatPeridinium balticumpossesses 2 Feulgen‐positive, membrane‐bound nuclei which divide synchronously. One nucleus has the typical structure of dinocaryotic dinoflagellates, while the other nucleus has a structure typical of eucaryotic organisms. Connections between each nucleus and the endoplasmic reticulum are common. Membrane‐bound vesicles are intimately associated with the nuclear envelope of the eucaryotic nu

ISSN:0022-3646    

DOI:10.1111/j.0022-3646.1973.00091.x

出版商:Blackwell Science Inc    

年代:1973

数据来源: WILEY