44 FUNGI 



The same action takes place in bread making, the escaping 

 CO 2 producing the so-called rising of the bread, and the 

 alcohol being evaporated in the process of baking. In wine 

 making, the alcohol produced may reach 15 per cent, if 

 enough sugar is present. Further production of alcohol is 

 then stopped, as an alcoholic solution above this strength 

 acts as an antiferment, and prevents the action of the yeast. 



The waste products of the respiration of the yeast plant 

 are nitrogen and carbon dioxide. These are removed from 

 the cell by diffusion. The breaking up of its protoplasm 

 under unfavorable conditions results in the formation of fat. 

 As a result of the physiologic processes of this minute plant, 

 there have been established several gigantic industries, which 

 furnish a large part of the food and drink of man. 



Reproduction. Under favorable conditions, such as suffi- 

 cient food, moisture and the right temperature, the yeast 

 plant reproduces asexually by " budding." Under these 

 conditions the protoplasm, which is increasing in amount, 

 extends the wall at one point in the form of a minute eleva- 

 tion. The bud increases to a certain size, when the nucleus 

 of the mother cell divides, one-half passing into the bud. A 

 wall then forms across the constricted portion of the bud, 

 separating it from the parent plant. 



A second method of reproduction occurs when the yeast 

 plant cannot obtain sufficient food. Under these conditions 

 its extermination is prevented by the division of the proto- 

 plasm into from two to four parts, around each of which a 

 thick wall is developed. These are the spores (very simple 

 ascospores), which can resist high temperatures and remain 

 dormant until such time as the conditions are again favorable 

 for their growth. Then each spore may develop into a yeast 

 plant of the normal form. 



