6 



Elementary Principles of Agriculture 



9a. Food Materials for Yeast. Secure two large bottles or fruit 

 jars, and fill both about two-thirds full of clear well-water. To one 

 jar add a teaspoonful of sugar and about as much of the white of 

 an egg. See that both are completely dissolved. Now add to both 

 jars small lumps of the ordinary "compressed yeast," or dry yeast 

 cake, secured from the bakery. Whichever is used, see that it is 

 well dissolved in a spoonful of water before adding to the jar. Stir 

 well and notice that the liquids are clear, or nearly so. Set aside in 

 a warm place, but not in strong light, and observe once or twice 

 a day for several days. The liquid soon becomes cloudy in the jar 

 to which the food was added, but not in the jar of water. The cloudy 

 effects are due to the large number of yeast plants formed. The 

 sugar and egg substance furnish the nourishment for their growth. 

 They do not multiply in the pure water. Yeast grows in the bread 

 dough because the dough contains all the substances needed for 

 the nourishment of the yeast plants. In the "dry yeast" these 

 tiny cells are in a dormant condition, like seeds. 



10. The Green "Pond Scums" belong to a class of 

 plants called algae (singular, alga). There are many kinds, 

 and nearly all of them are very 

 simple, being composed of single 

 cells, or small masses of cells. 

 Algae contain a green coloring 

 matter, which yeast-like plants 

 do not have. We shall later learn 

 something of the value of this 

 green coloring matter to the 

 plant. 



11. The Food Materials of 

 Green Plants are made from 

 water, carbonic acid gas, and the 

 simple minerals dissolved in the 

 natural waters of the soil. These 

 are combined to make all the substances necessary for 

 the nourishment and growth of their cells. They must 



simple one-celled form with 

 the cells embedded in a jelly- 

 like wall. B and C, forms 

 with the cells arranged in 

 chains. 



