28 



The ^■east plant consists of a single cell, which, at a certain stage, 

 sends out a bud from some part of its surface, which graduall)- increases 

 in size This bud may or may not remain attached to the parent stem. 

 If it does so, and the old stem continues to send out more buds, a mass 

 of cells is soon formed ; but, if each cell as it grows produces a bud, a 

 long chain of cells is formed. 



Under certain conditions (moist surface, plenty of air, favorable 

 temperature, and strong cells), small round bodies from two to eight in 

 number are formed inside the old cell, which are called spores. These 

 may remain dormant (that is quiet or asleep) for a considerable length of 

 time, but will germinate when placed in suitable food. They are usually 

 more resistant than the cells in the growing condition. Even the 





Fig. 32. A wine yeast, showing spore formation,— niagriifica- 

 tion, 1 000 diameters. From 2 to i spores may be seen in most of 

 the cells. 



ordinary cell lives for a considerable length of time when it is kept dry ; 

 and the dry yeast cakes, which are sold for bread-making purposes con- 

 sist of dried yeast cells mixed with starch or ground corn. 



There are several hundred varieties of the yeast plant, possessing 

 different properties, as there are many varieties of apples ; and as some 

 kinds of fruit are better than other kinds, so some varieties of yeast 

 are more suitable for use than others. 



Yeasts of different varieties are used in the manufacture of liquors, 

 such as beer, whisky, wine, cider, etc., and any of these yeasts could be 

 used in bread making ; but some would require twelve to fourteen hours 

 to raise the dough to the same extent as another would in seven or eight 

 hours. Figure 33 shows that some varieties of yeast produce more gas 

 than others. Thus, the variety in number i tube would be more 



