ASCOSPORES 



21 



of these becomes surrounded by a certain amount of reserve material, 

 and a spore wall is formed. The cell containing these spores (usually 

 four or eight) is the ascus. The ascus is formed less directly in many 

 other yeasts. In these the haploid ascospores fuse in the ascus two 

 by two, or the haploid cells which develop from the ascospores fuse 



Fig. 12. Various stages in the formation of ascospores in a yeast, Schizosaccha- 

 romyces octosporus. After Guilliermond. 



with each other or with an unfertilized ascospore. These fused cells 

 then develop into the ordinary yeast cell which is generally supposed 

 to have a single diploid nucleus. After considerable proliferation by 

 budding, some of these cells may undergo reduction division, form- 



FiG. 13. Various stages in the development of ascospores: A, Eremascus Jertilis; 

 B, Endomycopsis fibuliger. After Guilliermond. 



ing the ascospores, usually four in number. This process will be 

 elaborated in Chapter X. 



In the genus Endomycopsis and related fungi, a group of molds 

 closely related to and often classified with the yeasts, the formation 

 of ascospores is equally simple. Two contiguous cells in a filament 



