THE ULTRASTRUCTURE OF GLENODINIOPSIS STEINII (DINOPHYCEAE)

The freshwater dinoflagellate Glenodiniopsis steinii Wolsoszyńska was examined using computer-assisted three-dimensional reconstruction of serially sectioned cells observed with the transmission electron microscope and images from the scanning electron microscope. Vegetative cells contain ultrastructure typical of freshwater dinoflagellates including trichocysts, mitochondria, Golgi bodies, starch grains, and lipid bodies. The chloroplast is a single, multilobed structure, not multiple discoid chloroplasts as previously described. The “C” shape of the nucleus is apparently due in part to the size and location of the pusule.     

THE ULTRASTRUCTURE OF SAHNIA POLLEN (PENTOXYLALES)

The micromorphology and fine structure of in situ pentoxylalean pollen are described from the holotype of Sahnia laxiphora Drinnan and Chambers 1985 collected from the Lower Cretaceous (Valanginian-Aptian) of Victoria, southeastern Australia. Pollen grains are ovoid, monosulcate, and relatively small, averaging 26 μm in length. Exine ornamentation is psilate. The sporoderm is two-parted with the sexine staining lightly throughout and approximately six times the thickness of the more darkly staining nexine. The exine over the sulcus is typically strongly invaginated, and may or may not include an extremely thin sexine layer. The outer part of the sexine is homogeneous, while the inner part is composed of relatively large granules separated by irregular lacunae of various sizes; lacunae are most pronounced at the sexinenexine interface. Faint lamellae characterize the nexine in both apertural and nonapertural regions. Granular orbicules are often associated with the exine surfaces and also occur appressed to pollen sac walls along with lamellated tapetal membranes. Sporoderm ultrastructure is compared to that of nonsaccate pollen of other groups, and particularly to pollen of Bennettitales, Gnetales, angiosperms, and similar plants, to which the Pentoxylales have been thought to be closely related. Although Sahnia laxiphora pollen is not identical to that of any of these taxa, the strongest similarity is with pollen of Bennettitales.     

STUDIES ON PLANT CUTICLE: THE COMPOSITION OF THE CUTICLE OF APPLE LEAVES AND FRUITS

The levels of deposition of the waxy and cutin components of the cuticles of the mature leaves and developing fruits of the Merton Worcester and Cox's Orange Pippin varieties of apple over a period of 4 months are reported. The waxy materials on the leaves remain approximately constant at 20 μg./cm.², and the cutin at about 100 μg./cm.² of surface. The waxy and cutin deposits on the fruits increase markedly during the period of development, the wax and oil present on the surface and embedded within the cutin rising to 500 μg./cm.² and the cutin to a little under 1000 μg./cm.² of surface. Phenolic and acidic substances in the cuticles of the fruits are determined, and the possibility of their occurrence in surface deposits on the leaves is discussed.
An examination is made of the effect of nutrient deficiency upon the formation of waxy and phenolic substances in the leaves. Nitrogen deficiency in Worcester Pearmain leaves leads to a reduced deposition of waxy materials, and nitrogen, phosphorus and potassium deficiency results in higher contents of phenolic compounds. The separation and nature of the waxy covering on leaves, the effect of environmental conditions on its formation, and its importance in relation to the application of crop protection chemicals are discussed.     

TRANSPORT OF UNCONTAMINATED AND MOLLUSCICIDE-CONTAINING FOOD IN THE DIGESTIVE TRACT OF THE SLUG DEROCERAS RETICULATUM (MULLER)

By X-ray analysis of food transport in the alimentary tractof Deroceras reticulatum it was shown that even ten hours afteringestion of a thorium sulfate-containing bait, this materialcan be detected in the crop. After 2.5 h, some parts of labelledfood passes down from the anterior to the posterior part ofthe gut. After 13 h, thorium sulfate-containing material canbe observed only in the gut. After 19 h, no more labelled materialis present in the alimentary tract of the animals. After addition of Cloethocarb, the animals feed on only smallamounts of food. The labelled material only enters the anteriorpart of the gut. After ten hours, the food does not move anymore and does not leave the crop even 19 h after feeding. After molluscicide application, the crop epithelium is moreinfolded than in control animals and the cells are elongated.After 30 h, cells protrude into the lumen of the digestive tract. (Received 11 May 1992; accepted 26 June 1992)     

ULTRASTRUCTURE OF THE FRUSTULE OF TRICERATIUM FAVUS (BACILLARIOPHYCEAE)1,2

New structural details of the frustules of the diatom Triceratium favus Ehrenberg seen in the scanning electron microscope are reported. Significant new observations concern the pores of the hexagonal chambers, accessory structures (spines, dendritic processes) on the outer surfaces of the hexagonal chambers, the value margins and girdle structure.     

ULTRASTRUCTURE OF THE SHOOT APEX OF TOMATO (LYCOPERSICON ESCULENTUM)

The vegetative shoot apical meristem of tomato (Lycopersicon esculentum Mill.) was examined at the ultrastructural level. The meristem consisted of a surface layer that was different from the rest of the meristem and was unique among the dicotyledonous species. The cells of the surface layer contained large distal vacuoles with relatively large electron-dense inclusions, proplastids with membrane-bound inclusions (MB), and differentiating chloroplasts. In addition, periclinal and oblique divisions were observed in the surface layer cells along with anticlinal divisions. The cells of the subsurface layers contained small vacuoles with fewer inclusions as well as proplastids of various shapes but without MB. Differentiating chloroplasts were not observed in these cells, but autophagic vacuoles at various stages of development were present. The normal complement of cell inclusions, e.g., the mitochondria, golgi bodies, endoplasmic reticulum (ER), ribosomes, and microtubules were observed in subsurface layers, and in many cells the ER was observed to be continuous with the outer membrane of the nuclear envelope and with the plasmalemma. Further below in the meristem, cells contained both the proplastids and differentiating chloroplasts with MB. In the latter, the outer membrane of the MB was found to be continuous with the developing lamellae, suggesting that MB probably serve as the storage centers for lamellae membranes. Near the base of the meristem, in the pith-rib meristem, enlarged cells containing large vacuoles and differentiated chloroplasts were present.     

THE ULTRASTRUCTURE OF THE SALT GLANDS OF CYNODON AND DISTICHLIS (POACEAE)

The epidermal salt glands of the grasses Cynodon and Distichlis consist of a small outer cap cell and a large, flask-shaped basal cell. The wall of the basal cell is contiguous with those of the adjacent epidermal cells and underlying mesophyll cells. The basal cell is connected symplastically with all adjoining cells via plasmodesmata. The outer, protruding portion of the glands is covered by a cuticle continuous with that of the adjoining epidermal cells. However, the lateral cell walls of the glands are not incrusted by this cuticle. The cap cell wall has a loose, mottled appearance quite different from the compact striated appearance of the basal cell wall. The cap cell is characterized by dense cytoplasm containing many organelles and a varying number of small vacuoles. The basal cell cytoplasm is distinguished by the presence of an intricate system of paired membranes that are closely associated with mitochondria and microtubules. These membranes are infoldings of the plasmalemma that originate adjacent to the wall separating the cap and basal cells. The space enclosed by the paired membranes, therefore, is an extracellular channel that is open only in the direction of secretory flow. The consistent orientation of this system of paired membranes suggests that it represents a structural specialization which is directly and functionally involved in the secretory process. The close association of mitochondria and microtubules with the paired membranes implies that these structures are also functionally related to the secretory process. Finally, the results of this study indicate that these glands are ultrastructurally similar to those of Spartina and that the glands of these three grasses are structurally distinct from those of dicotyledonous plants.     

THE ULTRASTRUCTURE OF MEIOSPORES OF COLEOCHAETE PULVINATA (CHAROPHYCEAE)1

In view of the relative importance of reproductive cell ultrastructure in phylogenetic and systematic studies of green algae, we investigated the fine structure of germinating zygotes and meiospores of Coleochaete pulvinata Braun. Meiospores have a flagellar apparatus very similar to that of zoospores and spermatozoids of the same species. Meiospores differ from zoospores and spermatozoids of C. pulvinata in having pyramidal body scales similar to those present on zoospores of C. scutata. Meiospores of C. pulvinata had as many as twice the number of spline microtubules as zoospores, and four times the number present in splines of spermatozoids of the same species. Developing meiospores of C.pulvinata, like those of other Coleochaete species, are individually surrounded by chamber walls. These differed from vegetative cell walls in lacking plasmodesmata. Moreover, the chamber walls in germinating zygotes of C.pulvinata stained a cobalt blue color with resorcinal blue, and fluoresced yellow in the presence of aniline blue, thus exhibiting the staining characteristics of callose. In location, morphology and presence of callose, chamberwalls resemble “special walls” of land plants, they may represent a charophycean spore development preadaptation useful in the evolution of walled spores characteristic of land     

ULTRASTRUCTURE OF THE GAMETE OF PEDIASTRUM DUPLEX (CHLOROPHYCEAE)1

Gametes of Pediastrum duplex Meyen were investigated ultrastructurally, with emphasis on the flagellar apparatus. The cells are naked, biflagellate, and measure approximately 2.5 × 8 μm. Distinguishing them from zoospores is their possession of an eyespot and mating structure (the apical cap), and their lack of the peripheral band of cytoplasmic microtubules involved in colony formation. Four featurs of the flagellar apparatus are especially noteworthy: (1) the basal bodies are directly opposed and (2) are interconnected via their cores, (3) the central portion of the distal fiber is elaborated into an unusual ribbed structure which overlies the striated microtubule-associated component (SMAC) of the two-membered rootlets, and (4) the X-rootlets are dissimilar in microtubular number. The smaller X-rootlet consists of four microtubules in a three over one (3/1) configuration, whereas the larger has been found to be either 5 / 1, 6 / 1 or 7 / 1. The former rootlet extends past the nucleus whereas the latter extends down the opposite side of the cell, passing near the eyespot. The first two of these flagellar apparatus features have been previously noted in other motile cells of the Hydrodictyaceae. Although not specifically mentioned, published micrographs suggest the presence of the latter two as well, which may indicate that all four flagellar apparatus features are characteristics of all motile cells in the Hydrodictyaceae.     

A COMPARISON OF THE LIFE CYCLES OF THE SLUGS DEROCERAS RETICULATUM (MULLER) AND ARION INTERMEDIUS NORMAND ON PERMANENT PASTURE

Life cycles of the slugs Deroceras reticulatum and Arion intermediuswere compared over a four-year period on permanent pasture nearOvingham, Northumberland. Both species were semelparous, theirlife cycles taking about one year. D. reticulatum, unlike A.intermedius and other species, had two overlapping generationsthat laid their eggs in late spring and autumn respectivelyand also had one instead of two immature phases in its lifecycle. The pattern and rates of growth for the immature phasesin the life cycle of A. intermedius differed markedly from thosedescribed under laboratory conditions. Growth in the infantilephase was delayed in the field by low winter temperatures whilesecond stage growth was usually delayed in late spring by dryconditions. The life cycle of A. intermedius appears to be synchronisedby seasonal changes in photoperiod, unlike that of D. reticulatum.Growth in D. reticulatum continued throughout the winter monthsexcept under exceptionally cold conditions and was not usuallydelayed by dry conditions in spring. The size of hermaphroditegland relative to body weight in D. reticulatum reached a maximumin mature-unmated slugs and then became progressively smalleras the slug approached the post-reproductive stage which wasrelatively brief. Exceptionally dry conditions in 1962 delayedthe development of the hermaphrodite gland, the maximum sizereached was significantly reduced and fewer eggs were laid. (Received 17 September 1987; accepted 2 January 1988)     

荒漠竹节虫卵的超微形态结构观察

利用扫描电子显微镜和光学体视显微镜,首次对仅分布于中国新疆及毗邻中亚细亚地区的、稀见荒漠拟态昆虫--荒漠竹节虫Sceptrophasma bituberculatum(Redtenbacher)卵的外部形态和超微结构进行了观察和描述,探讨其对干旱荒漠环境的适应性结构特征.     

河鲈锚首吸虫体壁的超微结构观察

寄生鳜鳃部的河鲈锚首吸虫的体壁由表皮合胞体、基板、环肌、纵肌和表皮细胞核周体所组成。合胞体顶部质膜起伏形成表皮的嵴纹,基部质膜折叠形成指状突起伸入到合胞体中。合胞体表面覆盖着一层糖萼。河鲈锚首吸虫的表皮中含有四类分泌体,即电子致密的分泌颗粒、中等电子致密的分泌颗粒、有膜包围的电子稀疏的分泌体和多囊体．可见分泌体和合胞体基质通过胞吐作用排到体外,未见吞饮小泡,推测表皮的主要功能在于分泌和渗透压调节而非营养吸收。在外侧头瓣的乳突状结构所在处,合胞层较薄,基板平滑,在实质组织中的一腔体样结构中可见囊状体、电子致密度各异的颗粒体、泡状体和电子致密的基质团,神经突起分布于腔体周围,这类乳突可能代表一类新的非纤毛感受器类型。     

THE PENETRATION OF THE INSECT CUTICLE BY ISOMERS OF BENZENE HEXACHLORIDE

The penetration of the α-, β-, γ- and δ-isomers of benzene hexachloride through the insect cuticle has been studied by a micro-colorimetric technique.
Grain weevils were exposed for varying periods to deposits of pure isomers of benzene hexachloride on filter-paper. The amounts of each isomer picked up by the insects were determined as two fractions, one 'outside' representing that which could be removed by cold methanol washing, and the other 'inside' recovered after decomposing the insects with nitric acid.
The results show that the amounts of each isomer taken up by the insects are in the approximate ratio of their solubilities in hydrocarbon solvents, and that the y-isomer penetrates through the outer layers of the insect integument much more rapidly than the other three isomers tested.
On the basis of these results it is concluded: (i) that the first stage of pick-up of insecticide by the insects is simple solution of the insecticide in the outer waxy covering of the epicuticle; and (ii) that structural effects play an important part in the penetration through the insect cuticle as well as in toxic effects at the site of action.     

ULTRASTRUCTURE AND HISTOCHEMISTRY OF THE POSTERIOR OESOPHAGUS OF NASSARIUS RETICULATUS (LINNAEUS)

The posterior oesophagus of N. reticulatus (Linnaeus) consistsof two histologically distinct regions. The epithelium of thethickened segment in the visceral haemocoel is virtually uniform.The cells are lipid-rich and can take up lipid from food. Inaddition, enzyme histochemistry indicates a capacity for theuptake of sugars and amino acids. The basal plasmalemma is elaboratelyinfolded and associated with numerous elongate mitochondria,features indicating an active ion pump. The physiological roleof this pump is unknown. (Received 26 March 1985; accepted 10 May 1985)     

COMPARATIVE ULTRASTRUCTURE OF THE VALVES OF SOME CYCLOTELLA SPECIES (BACILLARIOPHYCEAE)1

Cyclotella atomus Hust., C. meneghiniana Kütz., C. comta (Ehr.) Kütz., C. antiqua W. Sm., C. michiganiana Skv., C. ocellata Pant., C. glomerata Bachmann, C. pseudostelligera Hust., and C. stelligera (Cleve et Grun.) V. H., were selected for ultrastructure investigations on the basis of their ready availability. Specimens were examined employing both transmission and scanning electron microscopy. Strutted processes, labiate processes, spines and other special features were surveyed in all species. On the basis of these observations the species of Cyclotella observed seem to be in one of 3 morphological groups, the meneghiniana group, the comta group, and the stelligera group.