FINE-STRUCTURAL FEATURES OF RHIZOMORPHS (SENSU-LATO) PRODUCED BY 4 SPECIES OF LICHEN FUNGI

Linear mycelial aggregates (rhizomorphs) produced by the squamulose li chens Toninia opuntioides, Squamarina cartilaginea, Lecanora rhizinata , and Acarospora scotica were examined by transmission electron micros copy (TEM). Cytological features typical of lichenized mycobionts were present, including concentric bodies and plasmalemma invaginations. S ome septa in rhizomorphs of S. cartilaginea and A. scotica appeared to be multipored. Septal pores were usually plugged by an electron-dense structure. Intrahyphal hyphae were common to abundant in the rhizomor phs of all four species examined. The wall of the invasive hypha was c ontinuous with inner wall layers of the cell of origin. Contacts betwe en adjacent hyphae involved wall dissolution and formation of new wall layers, leading to anastomosis and/or possibly to intrahyphal invasio n. Differentiation of an outer layer of collapsed cells in rhizomorphs of Squamarina cartilaginea and of extremely thick-walled cells Lecano ra rhizinata was evident, but no anatomical specialization comparable to the 'vessel hyphae' of non-lichen linear mycelial organs was observ ed. Enlarged spheroid or ovoid cells with dense cytoplasm, numerous mi tochondria and lipid reserves occurred in short chains in rhizomorphs of Acarospora scotica; infrequently, similar cells were observed singl y in those of Squamarina cartilaginea. These cells were reminiscent in shape of certain types of oil hyphae found in endolithic lichens, alt hough often the lipid content of the enlarged cells was not particular ly pronounced.