LIGHT AND ELECTRON-MICROSCOPY OF A DISTINCTIVE VA MYCORRHIZA IN MATURE SPOROPHYTES OF OPHIOGLOSSUM-RETICULATUM

The mycorrhiza of Ophioglossum reticulatum was studied by means of lig ht microscopy, scanning and transmission electron microscopy. An asept ate muitinucleate fungus forms intracellular hyphal coils in root cort ical cells. Single hyphae from these coils penetrate adjacent host cel ls and form arbuscules. In the youngest infected host cells arbuscules are of a coralloid shape, but on older host tissue, they develop larg e, terminal vesicular swellings. The arbuscules are surrounded by matr ix material and the host plasmalemma. Host cytoplasm and plastids incr ease with arbuscule development and starch disappears. Living and dege nerated arbuscules may occur within the same host cell. Intercalary hy phal swellings and single terminal vesicles are found in the older hos t tissue where arbuscules have degenerated.