3-3 THE YEAST CELL 



should contain by-products of yeast growth and possibly some sub 

 stances produced by the death and disintegration of yeast cells. 

 Genetical analysis requires an abundance of large viable 4- 

 spored asci, and an investigation of the conditions controlling sporu- 

 lation in Saccharomyces cerevisiae was made. The objective was 

 to develop an optimal medium for the production of spores, and es- 

 pecially to reduce the time required to obtain them. Grape juice 

 was found a satisfactory presporulation nutrient for some yeasts 

 but was ineffective with others. Gorodkowa's medium and carrot 

 agar were ineffective generally. Yeasts vary extremely in their 

 capacity for sporulation, and it was essential to develop a medium 

 that would activate even the poorest sporulating cultures. The study 

 of presporulation nutrition was extended and an extremely effective 

 combination of nutrients developed. There seems to be a general 

 correlation between the size of the ascospores and their vigor, and 

 media which produce the larger spores were favored. Since the 

 larger asci are easier to dissect, this characteristic has a two- 

 fold advantage. Immature spores are usually nonacidfast, and com- 

 ponents of the media which reduce the number of such spores to a 

 minimum have been selected. Throughout this work counts were 

 made or percentages of sporulation estimated on the slides after 

 staining, but different numbers of strains as well as different strains 

 were tested on the various media and changes in technique devel- 

 oped as the work progressed. Sporulation was more abimdant di- 

 rectly on the slants of simple potato agar than on most of the media 

 tested, but this medium was not used because the asci were small 

 and predominantly 2-spored, even when cultures genetically capable 

 of producing 4-spored asci were used. Cells grown on a substrate 

 containing sugar became much larger than those grown on a vege- 

 table slant. Sporulation does not occur on a rich sugar medium, 

 and therefore transfer to gypsum is required. However, since this 

 extra step results in the production of larger spores, the advantage 

 more than counterbalances the extra work. 



MEDIA AND METHODS 

 The following presporulation mediimi was finally chosen: 



Beet (leaves) extract (100 gms. per 100 cc. boiling water) .10 cc. 



Beet (roots) extract (100 gms. per 100 cc. boiling water) . . 20 cc. 



Apricot juice (canned) 35 cc. 



Grape juice (bottled) 16.5 cc. 



Yeast (dried) 2 gm. 



Glycerin 2.5 cc. 



Agar 3 gm. 



CaCOg 1 gm. 



