Chapter 14

Knowledge of the sequence of morphogenetic changes in the development of sporangia and spores in the watermolds was first arrived at by traditional -and sometimes rather imprecise -cytological methodology (Chapter 12) or by simple observational means (Chapters 7, 8). In either case, the resulting information was limited in scope, but it is now possible by analyzing elements of the subcellular structure of the asexual apparatus to confirm, modify, or reject previous views on sporangial morphology in these fungi. That certain major events in the morphogenesis of the sporangium need not be reappraised in the light of information from ultrastructural study is testimony to the keen perception and deductive reasoning of some of the pioneer investigators. The development of the asexual apparatus -as it was perceived using light microscopy -proceeds through a sequence of structural changes leading to the release of motile or encysted spores (Fig. 12). The ultrastructure of the various events that cleave a single protoplast into a number of asexual cells, and of the products of that segmentation, is treated in this chapter.