A LIGHT-MICROSCOPIC AND ELECTRON-MICROSCOPIC STUDY ON A VESICULAR-ARBUSCULAR HOST-FUNGUS INTERACTION IN GAMETOPHYTES AND YOUNG SPOROPHYTES OF THE GLEICHENIACEAE (FILICALES)

Gametophytes and primary roots of young sporophytes of the Gleicheniac eae were studied by means of light- and electron microscopy. An asepta te fungus invaded the gametophyte tissue through the rhizoids. The fun gus spread within the thickened midrib forming intracellular hyphal co ils. The latter gave rise regularly to arbuscules which were cytoplasm ic in the young part of the midrib. In the older midrib, arbuscules de generated and vesicles occurred. With arbuscular development, host cyt oplasm and cell organelles increased and starch disappeared from plast ids. The fungus formed globose spores inside the rhizoids. The gametop hyte fungus did not transverse the gametophyte-sporophyte junction. Pr imary roots shorter than 2 mm were not infected. Primary roots longer than 2 mm showed vesicular-arbuscular mycorrhiza with a completely int racellular development of the fungus.