Electron microscopic studies oiSphagnum lindbergii (Schimp.) and S. riparium (Angstr.) bave revealed tbe presence of intracellular organisms sucb as blue-green algae, green algae, bacteria and fungi.Nitrogenase activities of tbese Sphagnum mosses were found to be related mainly to tbe presence of intracellular Nostoc filaments. Tbe appearance of nitrogen-fixing blue-green algae witbin bryopbytes is tbus not restricted to liverworts. The association is likely to be of ecological importance as it .seems to occur in very acid babitats generally lacking blue-green algae.Possible interrelations between tbe moss, tbe blue-green algae and different types of bacteria are discussed.

Free-living nematodes-Panagrellus sp., Turbatrix aceti, Caenorhabditis elegans and C.hriggsae-were each fed to the fish Danio sp. and the process of their digestion, in the fish alimentary canal, was studied by light and electron microscope.Almost no identifiable nematodes were found in the fish gut when the digestion period was 3 h or more, except for buccal capsules of the four studied species, males' spicules of Panagrellus sp. and Turbatrix aceti and egg-capsules of the Caenorhabditis species. These structures could serve as indicators that the nematodes had been preyed on and digested by the fish.Differences in the mode of digestion were noticed between the various species of nematodes studied, after a period of0.5-I h, in the fish gut. In Panagrellus sp. and T. aceti disintegration of the soft inner tissues occurred mostly at the anterior or posterior ends of the nematode's body, while in Caenorhabditis the majority of digested nematodes were affected at both ends or evenly along the entire body. Digestion seemed to be initiated mostly at the nematodes' body apertures: mouth, anus or cloaca, and vulva which could be due to a more vulnerable cuticle around those areas. Disintegration proceeded from the soft inner parts to the more resistant cuticle that was finally disintegrated. Ofthe three layers of cuticle the most resistant were the external cortex and the basal layers.

SUMMARYFilamentous cyanobacteria are found intercellularly in a zone between inner and outer cortex of coralloid roots, growing below the soil surface, from the cycad Zamia skinneri Warsc. The zone is transversed by elongated Zamia cells interconnecting the two cortex layers. These host cells show characteristics of transfer cells, i.e. considerably expanded cell walls, numerous mitochondria and amyloplasts. An involvement of these cells in the transfer of solutes between cyanobacterium and host is therefore suggested. The cyanobacterium belongs to the genus Nostoc and consists of vegetative cells, heterocysts and a few akinetes. Healthy vegetative cells contain thylakoids with phycobilisomes, carboxysomes, cyanophycin and glycogen granules. Thus, no distinct subcellular modifications due to a symbiotic mode of life in the absence of light were observed.

X-Ray microanalyses were made by scanning electron microprobe on thin sections of seeds of Cramhe abyssinica. Linear scan profile and multilinear scan image of X-ray emissions for magnesium, calcium and sulphur were compared. It was also possible to detect these elements in point analyses in the globoid region in the protein bodies of the seed. Microanalyses were also made witii the EDAX system :and with EMMA analytical electron microscope.

The obligate endoparasitic fungus Meria coniospora lives its entire vegetative life within infected nematodes. Conidia of M. coniospora infect the nematode Panagrellus redivivus mainly in the mouth region. The infection, starting with adhesion of conidia to the nematode surface, growth of trophic hyphae, production of conidiophores and conidia, was followed using light, scanning and transmission electron microscopy.