272 TEXT-BOOK OF FUNGI 



suitable for this work. Wager placed compressed yeast in 

 a tumbler containing a five per cent, saccharose solution in 

 water ; a scum soon formed on the surface, and as evapora- 

 tion proceeded, the cells that were left on the side of the 

 glass produced endospores. The number of endospores 

 varies from two to four, the latter number being most 

 frequent. So far as is at present known, endospores in 

 species of Saccharomyces are produced by free-cell forma- 

 tion without the intervention of any sexual process. In 

 some other genera, however, a true sexual act precedes 

 the formation of endospores. Barker has shown that in 

 a genus he has called Zygosaccharomyces, conjugation of 

 two cells precedes the formation of endospores. Two cells 

 lying close together produce small, bud-like outgrowths 

 opposite to each other ; these continue to grow into beak- 

 like structures until they meet. The walls dissolve at the 

 point of contact, and communication between the two 

 cells is effected. After fusion of the two cells is com- 

 pleted, the protoplasm in each cell undergoes certain 

 changes and becomes contracted into two spheres, which 

 finally develop into spores surrounded by a distinct cell- 

 wall. The number of spores produced is variable, two in 

 each mother-cell being the most usual number. A fusion 

 of two nuclei after conjugation, and the subsequent 

 division of the fusion-nucleus to form the nuclei of the 

 spores, was observed. Ordinary vegetative budding also 

 occurs, exactly as in S. cerevisiae. 



In the genus Schizosaccharomyces^ described by Beyer- 

 inck, in which, in place of budding, when a cell reaches 

 a given size, a transverse septum is formed, and the two 

 daughter-cells become separated by the splitting of the 

 septum, hence the generic name. Guilliermond has shown 



