HEM1 ASCOMYCETES 



153 



In Schwanniomyces occidentalis, on earth in the Virgin Islands, dynamic 

 sexuality is lost and morphologically only a few traces remain. At sporu- 

 lation the cells which will develop to asci form longer or shorter copulation 

 processes. Their sexual attraction is so small that they are only seldom 



Fig. 94. — Torulaspora Rosei. Development of asci. (X 1,000; after Guillermond, 1912.) 



able to join and, even when this happens, they no longer come into open 

 communication but change parthenogenetically to asci. 



From this species, it is only a short step to purely parthenogenetic 

 forms in which no traces of sexuality are retained either dynamically or 

 morphologically and in which the ascospores under suitable conditions 



Fig. 95. — Saccharomyces cerevisiae. 1 to 4. Formation of sprout cell with amitosis of 

 nucleus. (X 1,500.) 5 to 11. Development of sprout cell to ascus and germination of 

 ascospore. ( X 750.) (After Guillermond, 1902, 1904.) 



are formed directly as endospores in any vegetative cells (Fig. 95, 5 to 9). 

 This parthenogenetic group contains many technically important species 

 discussed in detail in Lafar, Handbuch der iechnischen Mykologie, as 

 Saccharomyces cerevisiae, the group of beer yeasts; S. Pastorianus, cause of 

 a beer disease; S. ellipsoideus, the collective type of the more important 

 wine yeasts; S. minor, a yeast of bread making; and Pichia membranifa- 



