22 



THE RUBBER TREE BOOK 



for many centuries that the cultivation of pea or bean-bearing 

 plants added greatly to the fertility of the soil, but the reason 

 of this was not discovered till the above-mentioned date. 



The whole science of fermentation in all its varied aspects 



FIG. 5. Bacterial Nodules on Roots of Mimosa. 



is based solely upon the chemical changes affected by bacteria. 

 The bread we daily eat is fermented and leavened by the 

 action of the yeast, otherwise it would be a sodden, unappetizing 

 mass of dough. By the action of bacteria certain sugars are 

 transformed into alcohol; by other bacteria alcohol is con- 



