Photoreceptors of anchovies Anchoa mitchilli and A. hepsetus consist of normal rods and two unusual kinds of cones. The latter lie in single vertical rows, and the rods lie between them. Both participate in photomechanical movements, and movement of the cones is closely coordinated with that of pigment cell processes. There are long cones having a cuneate outer segment and short cones having a bilobed outer segment. Long and short (bifid) cones alternate within a row and are staggered between adjacent rows. Both kinds possess calycal processes; long cones have a lateral sac or accessory outer segment. The long and short cones are associated to form a structure called a cone unit, which consists of the outer segment and ellipsoid of a long cone joined to two outer segment lobes of two adjacent short cones. The lobes of the latter are partly enclosed by the ellipsoid of the long cone. A cone row consists of a row of cone units isolated from each other by processes of the pigment epithelium containing stacks of guanine crystals which form a tapetum. Dorsal and ventral faces of inner segments have contact zones characterized by subsurface cisternae. Lamellae in the cone outer segments are arranged longitudinally with respect to the cell axis and short and long cone lamellae are perpendicular to each other; lamellae of the rods are transverse. Long cone lamellae are perpendicular to the cone row, and in the central retina are almost horizontal to the long axis of the body. Some vesicular/tubular structures also occur in the cone outer segments. Outer and inner segments of cones are joined by a broad connecting structure containing a stalk and root portion corresponding to a modified and reduced cilium shaft and centriole, respectively. The rod has a typical connecting stalk. Mitochondria of cone ellipsoids have expanded perimitochondrial spaces between outer and inner membranes. The organization of the anchovy cones is compared with that of other vertebrates. It is suggested that the cone unit may be a two channel analyser for the detection of plane polarized light and function in conjunction with the overlying reflector of regularly arranged platelets.

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Ascochyta fabae Speg. f.sp. lentis (Gossen et al. 1986) causes lesions on the leaf, stem, and pod of lentil (Lens culinaris Medik.), thereby reducing seed quality and yield. Lesion formation was studied in two cultivars, Laird and Invincible, using light and electron microscopy of intact and excised leaves and stems inoculated with spore suspension. Spores germinated usually within 6 h of inoculation and germ tubes grew for varying distances along the leaf surface before forming an appressorium, sometimes within less than 10 h. A penetration peg then either directly entered the underlying epidermal cell, or grew as a subcuticular hypha for a short distance before entering the cell. The first response of epidermal cells to presence of the fungus was an aggregation of cytoplasm abutting the site of infection. This was followed closely by deposition of a papilla. Some relatively thick papillae were seen at 29 h postinoculation. The fungus then grew into the papilla and formed an infection vesicle. In susceptible host cells, the protoplasm became necrotic before hyphae grew into the lumen of the cell from the infection vesicle. In more resistant cells, the infection vesicle often became surrounded by electron-dense wall material developed by the host. The fungus remained in susceptible epidermal cells for up to 4 days, amongst remnants of the protoplast, before spreading to the adjacent mesophyll. Hyphae grew into intercellular spaces of the mesophyll and remained there for 2 – 3 days before penetrating the cells. The mesophyll reacted in a similar way to infection as did the epidermis, with only host cells close to the fungus becoming affected. Cultivar Laird was found to be less susceptible to infection than cv. Invincible. At the structural level, the infection process was found to be similar except that in cv. Laird the infection vesicle more frequently became surrounded by electron-dense wall material formed by the host. In stem tissue of cv. Laird the middle lamella was also occasionally thickened with electron-dense material deposited on either side of it. After the degeneration of host tissue, pycnidia-bearing spores were formed 10 – 14 days after inoculation of the leaf. Key words: Ascochyta, lentil, ultrastructure, infection process.

A correlated thin-sectioning and freeze–fracturing approach was used to reveal the ultrastructure of endogenously dormant teliospores in the smut fungus Entorrhiza casparyana (Magn.) Lagerh. Conventional fixation and embedding methods yielded poor preservation of the wall and protoplasm. Successful preservation was achieved by fixing frozen and cryosectioned spores in glutaraldehyde and subsequently processing by standard procedures for transmission electron microscopy. Freeze–fracturing provided cross- and contour-fractured views of the protoplasm and the different layers of the wall. The wall is thick, consisting of three main layers: outer, middle, and inner, with the outer and inner layers further differentiated into zones. The warty zone dominates the outer layer and consists of radial protuberances (warts) with the regions between filled to varying degrees with similar wall material containing electron-transparent lamellae. The extent of differentiation of the warty zone is reflected in the surface morphology of the spores, which ranges from verrucose to almost smooth. At the base of the outer layer is an electron-translucent irregular zone. The middle and inner layers are regular in thickness around the spore, with the middle layer being the most electron dense. The inner layer is differentiated into three zones. The most distinctive is zone 2 which in freeze–fractured walls has an unique mosaic of striae. Cytochemical staining of the wall for polysaccharide material gives a positive reaction only for the warty zone. The protoplasm contains a single nucleus and is dominated by numerous spheroidal storage lipid bodies. Squeezed among the lipid bodies are organelles, believed to be microbodies, containing a granular matrix and often electron-transparent areas. These organelles failed to show catalase activity with the 3,3′-diaminobenzidine method. Occasional short profiles of endoplasmic reticulum cisternae, a few mitochondria with sparse cristae, dispersed small clusters of glycogen, and sometimes scattered ribosomes are also present in the cytoplasm. All these features are typical of dormant spores with a low metabolic activity.

Contrary to previous studies, cytokinesis has been observed on formation of the first anticlinal walls during initial cellularization in the endosperm of wheat. Typical phragmoplasts develop between the free nuclei in the peripheral cytoplasm, and the cell plates arising from these soon fuse with the wall of the central cell. The inner free margin of the walls, however, continues to grow towards the central vacuole within an advancing front of cytoplasm. Anticlinal walls arise around nuclei approximately simultaneously in different planes; three dimensionally the nuclei, therefore, become located within open-ended compartments of cytoplasm. The compartments then undergo cell division and develop periclinal walls by normal cytokinesis. These walls delimit the first complete layer of endosperm cells centrifugally and a new layer of open compartments centripetally. The inner compartments usually continue to grow centripetally until those from the opposite side of the grain meet. During this closing phase, along the zone where the compartments fuse, a further row of periclinal walls is formed. Subsequent immediate differentiation of endosperm involves the subdivision of the first-formed large endosperm cells into smaller cells.