PLANTS WITHOUT CHLOROPHYLL 137 



attached to them, sometimes there being several in a row. Yeast 

 cells reproduce very rapidly by a process of budding, a part of the 

 parent cell forming one or more smaller daughter cells which even- 

 tually become free from the parent. 



Conditions favorable to growth of Yeast. — Experiment. — Label three 

 pint fruit jars A, B, and C. Add one fourth of a compressed yeast cake to 

 two cups of water containing two tablespoonfuls of molasses or sugar. 

 Stir the mixture well and divide it into three equal parts and pour them 

 into the jars. Place covers on the jars. Put jar A in the ice box on the 

 ice, and jar B over the kitchen stove or near a radiator ; pour the contents 

 of jar C into a small pan and boil for a few minutes. Pour back into C, 

 cover and place it next to B. After forty-eight hours, look to see if any 

 bubbles have made their appearance in any of the jars. If the experiment 

 has been successful, only jar B will show bubbles. After bubbles have 

 begun to appear at the surface, the fluid in jar B will be found to have a 

 sour taste and will smell unpleasantly. The gas which rises to the surface, 

 if collected and tested, will be found to be carbon dioxide. The contents 

 of jar B have fermented. Evidently, the growth of yeast will take place 

 only under conditions of moderate warmth and moisture. 



Carbohydrates necessary to Fermentation. — Sugar must be 

 present in order for fermentation to take place. The wild yeasts 

 cause fermentation of the apple or grape juice because they live 

 on the skin of the apple or grape. Various peoples recognize 

 this when they collect the juice of certain fruits and, exposing 

 it to the air, allow it to ferment. Such is the saki or rice ^vine of 

 the Japanese, the tuba or sap of the coconut palm of the Filipinos 

 and the pulque of the Mexicans. 



Beer and Wine Making. — Brewers' yeasts are cultivated with 

 the greatest care; for the different flavors of beer seem to de- 

 pend largely upon the condition of the yeast plants. Beer is 

 made in the following manner. Sprouted barley, called malt, in 

 which the starch of the grain has been changed to grape sugar by 

 digestion, is killed by drying in a hot kiln. The malt is dissolved 

 in water, and hops are added to give the mixture a bitter taste. 

 Now comes the addition of the yeast plants, which multiply rapidly 

 under the favorable conditions of food and heat. Fermentation 

 results on a large scale from the breaking down of the grape sugar, 



