SACCHAROMYCETACEAE 



301 



tAvo, nuclear division, there appear 8 — rarely 4 — spores (Fig. 57, 7-11). Often 

 the eopulatory canal is narrow so that the young ascus is shaped like a dumb- 

 bell between whose ends are divided the 8 spores. At germination, the spores 

 in the ascus swell, rupturing the ascus wall. Each spore thus liberated is 

 divided by a septum into two daughter cells. These cells continue to divide 

 similarly, and in some liquid media they form short branched filaments. 



Under unfavorable conditions, copulation may occur earlier, so that al- 

 ready in the ascus the ascospores copulate with ascospores of the same or a 

 neighboring ascus. In these cases the resulting zygote becomes an ascus di- 

 rectly without first forming a sprout mycelium. Other strains have a tendency 

 to become asporogenous; although they may still form eopulatory processes, 

 which may be functionless. In very rare instances, there seems to be a par- 



Fig. 57. — Schisosaccharomyces octosporus. Copvilation and development of asci (X750). 



(After Guilliermond 1905, 1917.) 



Fig. 58. 



-Zy gosacchuromyces Chevalieri siiowing stages of copulation. 



1913.) 



(After Guilliermond 



thenogenetic development of spores — 4 to an ascus. Copulation is normally 

 isogamous and the gametangial copulation is replaced by pseudogamy. This 

 also disappears and the cells, after unfruitful attempts at copulation, may 

 change parthenogenetically to asci. In 8chizosaccliaromyc.es Pomhe, an Afri- 

 can beer yeast, and in S. mellacei, from rum factories of Jamaica, many aspor- 

 ogenous strains are known, and in S. asporus, from arrack in Java, spores have 

 never been observed. 



In the Saccharomyceteae, we have two series of degeneration, one isog- 

 amous characterized by a smooth ascospore, the other heterogamous with a 

 rough one. In the simpler forms of the smooth-spored series, as in Zygosac- 

 charomyces, 2 cells form eopulatory processes toward each other, the nuclei 

 migrate into the bridge and fuse (Fig. 58, 1-3). This diploid nucleus divides, 

 both daughter nuclei migrate back into the copulating cells, there dividing a 

 second time forming 2 spores in each copulating cell. The whole cell, similar 



