1-8 THE YEAST CELL 



in a Mendelian manner in S. cerevisiae by S. bayanus hybrids. Sac- 

 charomyces bayanus does not ferment galactose but otherwise re- 

 sembles S. cerevisiae in fermentative ability. Saccharomyces pas- 

 torianus is responsible for bitter taste, disagreeable odor, and tur- 

 bidity in beer. It is a bottom fermenting yeast producing cylindrical 

 cells. Saccharomyces validus is a top fermenting yeast with long 

 cylindrical thread-shaped cells producing turbidity in beer. Sac- 

 charomyces turbidans grows well over a wide temperature range 

 producing elliptical cells and a very turbid broth. It is also unde- 

 sirable In beer because of the turbidity. 



CRITERIA FOR DISTINGUISfflNG 

 HAPLOPHASE AND DIPLOPHASE 



Winge (1935) distinguished clearly between haplophase and dip- 

 lophase yeast cultures, and we have corroborated his observation, 

 adding the concept that genes controlling mating type specificity 

 segregate at meiosis to produce two kinds of haplophases. I shall 

 summarize all the arguments, Winge* s reinforced by ours, for dis- 

 tinguishing haplophase and diplophase. Over four -fifths of the cul- 

 tures which one encounters are easily characterized by microscopic 

 examination. They are either obviously haploid or diploid, as shown 

 simply by size, shape and aggregation of the cells. The reasons for 

 classifying them are as follows: 



a. The large vegetative cell, which we call "legitimate diploids" 

 (fig. 1-7), produce viable 4-spored asci. These spores germinate 

 to produce smaller, usually round, cells which we call "haploid." 

 The latter multiply vegetatively, generally maintaining their spe- 

 cific cell-shape and size. 



b. Two of these smaller cells may fuse to produce a zygote 

 which on budding produces a large "diploid" cell capable of vege- 

 tative multiplication. While the large cell is undergoing vegetative 

 reproduction, it retains its characteristic ellipsoidal shape and size. 

 Under certain conditions this diploid cell can be induced to sporu- 

 late. Spores from it in turn produce haploids and the process can 

 be repeated indefinitely. 



o. The large cells which we recognize as diploids are extra- 

 ordinarily stable in their genetical characteristics when they are 

 grown under conditions in which sporulation does not occur. Trans- 

 ferring the cultures every forty -eight hours in broth is generally 

 sufficient to maintain the vegetative diplophase. Colonies produced 

 by plating out are not sectored; the plates do not show colonial vari- 

 ants. However, when haplophase (single ascospore) cultures of any 

 age are plated out, a variety of colonial variants appears on the plate 

 or the giant colonies are sectored. These facts are consistent with 

 the view that the large cells are diploid, thus minimizing the num- 



