254 



PHARMACEUTICAL BOTANY 



processes, and becoming dormant. Sometimes they enter the rest- 

 ing condition after a process of division, when each cell divides into 

 four parts, each of which becomes nearly dry and is surrounded by a 

 thick wall. Such cells are called ascospores, and their production 

 serves both as a method of multiplying the plant and of tiding over 

 adverse conditions. They can survive for a long time without 

 food or water, and can endure higher temperatures than the active 

 cells and almost any degree of cold. 



FIG. 127. Saccharomyces ceremsia. The form or variety known as brewers' top 



yeast. (Oberhefe.) 



The dried cells and spores float in the air as dust and so accomplish 

 a dispersal of tire organism. Doubtless most of them never again 

 meet suitable environment and so sooner or later perish. But some 

 will fall into favorable conditions and be able to multiply enormously 

 again, and so the species is continued. 



The general method of reproduction in Saccharomyces is that of 

 gemmation or budding. A small protuberance of the cell wall com- 



