ULTRASTRUCTURAL STUDIES OF SPORE WALLS OF ACAULOSPORA-MORROWIAE AND A-SCROBICULATA

Morphological and ultrastructural studies were used to determine spore wall structure in two Acaulospora species: A. morrowiae and A. scrobi culata. The spore wall of A. morrowiae is divided in three zones (A, B , C), each of which in broken spores separate into layers. Many featur es, such as a series of regularly distributed fibrillar layers of arch ed-appearing fibrils were clearly distinguishable. In A. scrobiculata, two zones were distinct in the wall: an outer zone, ornamented with d eep round-bottomed depressions which extended into several of the arch ed-like layers, and an inner zone formed by three distinct layers. The first layer of the inner zone had a radial arrangement of fibrils; th e two other layers were formed apparently by amorphous material. Arche d and radial fibrils have been found in spores of other Glomales but n ot in those of other groups of fungi. Spores of Acaulospora are simila r to those of certain other glomalean fungi. These and other data indi cate the uniqueness of spore walls in the Glomales.