HEMIASCOMYCETES 



271 



process of budding. When growth is very active, the 

 daughter-cells often give off buds before they separate 

 from the parent-cell, and it is not unusual to find buds of 

 various sizes and ages representing different generations, 

 adhering in a chain. 



Endospores are formed only under certain conditions. 

 The most important of these, according to Hansen, 



FIG. 67. i, Saccharomyces cerevisiae ; a, reproduction by 

 budding or gemmation ; b, cells containing ascospores. 2, 

 Zygosaccharomyces Barkeri, showing stages in the conjuga- 

 tion of two cells ; in the right-hand fig. four ascospores are 

 present. (Fig. i after Hansen, fig. 2 after Barker.) All 

 highly mag. 



are, that the yeast-cells must be placed on a moist, porous 

 surface, and have a plentiful supply of air. The most 

 suitable temperature is about 25 C. ; only young and 

 vigorous cells should be used for the experiment. Blocks 

 of gypsum, slices of carrot, and pads of blotting-paper 

 soaked in a solution of sugar have respectively proved 



