ZYGOSACCHAROMYCES CHEVALIERI 



217 



and rapidly on most solid media, such as slices of carrot, gelatin of 

 Gorodkowa, must agar and gelatin. Spores are also formed in scums 

 developed on beer wort. This sporulation is preceded by a hetero- 

 gamic copulation which has been described before. 1 This copulation 

 takes place between two gametes of variable dimensions and of dif- 

 ferent ages. One, the female gamete or macrogamete is an adult 

 cell, and very large; the other, the male gamete, or microgamete, is 

 very small, and young, generally a bud being detached from a mother 



Fig. 88-F. Heterogamic Copulation in Zygosaccharomyces 

 Nadsonia. 



cell. The two gametes unite by a copulation canal, then the con- 

 tents of the microgamete pass into the macrogamete which becomes 

 the egg. A wall is formed across the copulation canal which separates 

 the egg which soon appears as a separate cell. This changes into an 

 asc with from 1 to 4 ascospores, rarely more. By their form, the 

 spores are intermediate between those of the genus Pichia and of the 

 genus Willia but they approach those of Pichia most closely. Their 

 dimensions vary between 1.5 and 2.5 jit. 



The temperature limits for sporulation are: maximum, 37-38 C. 

 and the minimum, 8-10 C. The optimum is situated near 25 C. to 

 30 C. The spores form in from 18 to 20 hours at this temperature. 

 Germination of the spores is accomplished by ordinary budding. The 

 spores enlarge and lose their hemispherical shape when budding. 



1 Guilliermond, A. Sur un example de copulation heterogamique observe 

 chez une Levure. Comp. Rend. Soc. Biol. 1911. 



