Scanning Electron Microscopic Observations of a Moss-Fungus Association

Fungi were observed in the central hydroid strand of underground axes of Polytrichum commune Hedw. Hyphal strands appeared continuous from hydroid to hydroid in certain cases, apparently penetrating the lateral walls of hydroids. Hyphae were also observed on the epidermal surfaces of the rhizomes. Newly initiated gametophores and mature gametophores appeared robust and healthy. Whether the moss-fungus association is a host-parasite relationship or mycorrhizal-like was not determined. Hydroids of polytrichaceous mosses are generally recognized as a primitive type of water-conducting cell (Scheirer 1980). Several recent papers have considered the ultra- structure, histochemistry and evolutionary questions concerning hydroids, and conducting tissues in general, in mosses (Hebant 1977, Scheirer 1980). In a scanning electron micro- scopic study of the branching patterns of the underground stem system (rhizome) of Po- lytrichum commune Hedw., we observed fungal hyphae in the hydroids of the central strand. Since fungal associations with mosses are infrequently reported and not very well understood, the purpose of this paper is to report on the presence of fungi in the hydroids of P. commune. MATERIALS AND METHODS Sods of Polytrichum commune Hedw. were collected from an oak-hickory-white pine woodland, Lexington, Massachusetts and brought to the laboratory where individual gametophores were care- fully dissected from the soil. The rhizome of P. commune is a highly branched system from which new gametophores are initiated seasonally. Portions of newly initiated, subterranean gametophores were collected and fixed in 6% glutaraldehyde in a sodium cacodylate buffer, pH 7.2, for six hours at room temperature. Dehydration in an acetone series was followed by critical-point drying, after which the specimens were mounted on aluminum stubs, sputter coated with gold-paladium, and viewed with an AMR-1000 SEM at 20 kV.