78 BACTERIA, YEASTS, AND MOLDS 



uniform, smooth outline, but inside of them may com- 

 monly be seen some smaller bodies. There is usually 

 a somewhat rounded clear spot, as shown in Fig. 32, a^ 

 although in many cases instead of one we find two, three, 

 or four smaller ones (Fig. 32, b). These apparently rep- 

 resent only little drops of an oily liquid and have, so far 

 as we know, nothing very particular to do with the life of 

 the yeast plant. These drops are called vacuoles. No 

 further bodies can be seen in the yeast cell by ordinary 

 methods of study, although special microscopic devices 

 show that there are other bodies inside (Fig. 32, c). These 

 other smaller bodies need not, however, concern us. The 

 yeast cell thus described is quite unlike ordinary plants, 

 showing less resemblance to them than molds. But though 

 they bear no likeness to what we commonly call plants, 

 biologists are unanimous in their opinion that they are to 

 be classed with the molds as colorless plants and, hence, 

 as fungi. 



Yeast exists in three somewhat different states : (i) the 

 resting state ; (2) the growing state ; (3) the spore- 

 bearing state. The yeast in an ordinary yeast cake 

 already described is in the resting state. Such yeast 

 appears as in Fig. 32, a, each plant being a single oval 

 body or cell. It is alive but is not actively growing. 



The Growing State. When a little resting yeast is 

 placed in a solution which contains proper material for 

 food it begins at once to consume the food and grow. 

 As it grows it multiplies by a method known as budding. 

 Upon the sides of the yeast plants appear small buds (Fig. 

 33, a). Each bud at first appears as a little swelling on 

 the side of the larger yeast cell. This little bud increases 



