A New Foliicolous Didymium From Northern California

Optical microscopy of median sections through mature asci has revealed some interesting details regarding orientation of the ascospores. As seen in FIG. 3, the longitudinal ridges of adjacent ascospores touch each other at their edges. This results in a distinctive symmetrical configuration of the ascospores within the ascus which is also evident in asci observed in situ (FIG. 4). At the point of contact, the ridges of adjacent ascospores are slightly curved outwards at the edge, and thus appear fitted together in a mitered fashion (FIG. 5). The symmetrical arrangement of the ascospores with respect to outer-wall ornamentation suggests that the ascospores are spatially defined within the ascus. This spatial definition would be n-ade apparent in this species due to the nature of the spore-wall ornamentation. The data presented here do not indicate at what point in ascus development the ascospores are spatially defined. If the position of the ascospores is determined by spore-wall ornamentation then the ascospore arrangement is actually random, cytologically. If the position of the ascospores is a result of ordered nuclear relationships during the meiotic process, then the positioning of the ascospores is not random, but may be as well regulated as in cylindrical asci. Cytological studies at the ultrastructural and light levels of the entire sequence of events associated with ascospore and ascus development are in progress to determine which hypothesis is most probable.