Fine structure of mycorrhiza in Neottia nidus-avis (L.) L. C. Rich. (Orchidaceae).

The fine structural features of the symbiotic relationship between Neottia and the fungus Rhizoctonia have been examined. Different stages of development of the fungus within the orchid's root cells are described. The fungus-attacked Neottia cells show striking changes. The central vacuole is partly filled by a conspicuous plasmatic network while the nucleus enlarges considerably. Of special interest is the development of an extended rough-surfaced ER.