390 JSXPEHIMJSyTS WITH PLANTS 



with its cell-wall,^ and protoplasm lilled witli Hliiiiiii.ij: 

 drops or granules. The mode of multiplication can 

 also be easily made out: it is by budding, i. e., an 

 (intii'rowth from the cell becomes cut off, and forms a, 



new cell. The cells so pro- 

 duced often hang together 

 in chains (Fig. 213). 



The bubbles of gas 

 which rise in the liquid 

 are practically pure carbon 

 Yeast-cells budding. dioxide. At the same time 



that evolution of gas goes on, alcohol is formed, and 

 the sugar disappears (as can be shown by tasting the 

 liquid). Chemical analysis shows that the sugar is 

 liroken up by the action of the Yeast into alcohol and 

 carbon dioxide. The presenci^ of alcohol can be shown 

 by cautiously heating the liquid in a cup until enough 

 vapor forms so that it may be ignited by a match: 

 we may also distil off the alcohol by means of tlie 

 a]ii)aratus shown in Fig. 9."). 



This process is very general in nature. Nearly all 

 fruits have Yeasts on their surfaces which cause fer- 

 mentation when the fruit b(\giiis to decay, converting 

 the sugar present into alcohol and carbon dioxide. 

 Test some ripe grapes by crushing them, covering them 

 with water and allowing them to stand for a time; 

 when fei-mentation occurs examine for Yeasts. 



1 If there is any difficulty in seeing the cell-wall, shrink the cells by the 

 use of a little glycerine or strong salt solution. 



