THE YEAST FUNGI, 



X49 



/A* iii length, single or with hranches composed of 

 short chains. Three or four spores in the mother cell, 

 1 5 /Lt in diameter. Employed in the brewing of beer ; 

 in the low fermentation which goes on slowly between 

 4 and 10 C., the yeast is deposited at the bottom of 

 the vessel (unter-hefe) , and the cells are for the most 

 part single, or united in small numbers. In the high 

 fermentation, which takes place between 14 and 18 C., 

 the stream of carbonic acid carries up the yeast to the 



Fig. 27. -Saccharoinyces cere visile 



(yeast). 



A, slightly enlarged. 



H, low yeast highly magnified. 



C, upper yeast highly magnified. 



Fig. 28. Spore formation in 

 saccharomyces cerevisiffi. 



(After Rees.) 



a, b, cells with several vacuoles. 

 c, cell with uniform granular 



contents. 

 (I, four plasma portions. 



e, young spores arising from 



these. 



f, the same with double con- 



tours. 

 <7, free spores after solution of 



the membrane. 

 A, commencing sprouting of the 



spores. 



surface of the fluid, and this upper yeast (dber-hefe) 

 contains branched bands composed of several buds. The 

 upper yeast is employed in baking to raise the dough ; 

 it further serves for the formation of the compressed 

 yeast. On plates of nutrient gelatine the colonies form 

 after two days small white points, so long as they are 

 beneath the surface ; as soon as they reach the surface 

 they form somewhat more extensive white drops, or dry 

 masses. Under a low power the colonies appear 

 yellowish-grey in colour, and with a rough contour, like 



* The mark M, which is much used in the following pages, signifies 

 a micromillimeter=0'001 of a millimeter. 



