THE FINE-STRUCTURE OF ASCOSPORE SHAPE AND DEVELOPMENT IN CERATOCYSTIS-FIMBRIATA

Ascospore development in Ceratocystis fumbriata Ell. and Halst. commen ced in an eight-nucleate ascus. A single vesicle formed along the peri phery of the ascus from fragments of ascospore delimiting membranes, s urrounded all eight nuclei and eventually invaginated, first forming p ouches with open ends, then finally enclosing each of the eight nuclei in a separate sac, thus delimiting ascospores. Pairing of the ascospo res followed and brim formation occurred at the contact area between t wo ascospores. Osmiophilic bodies contributed to the formation of brim -like appendages by fusing to the ascospore walls. Additional brims we re observed at opposite ends of the ascospores giving them a double-br immed appearance.