CHAPTER IV 



THE SUBSTANCES OF WHICH A LEAF IS COMPOSED 



WE can readily understand that the decaying vege- 

 table stuff supplies food for the plant, but we have 

 not yet decided whether the broken-down rock also 

 supplies it with food. 



We can best decide the matter by examining a 

 leaf itself, and seeing of what it is composed. 



Experiment 21 



Pick a few leaves and weigh them. About one 

 quarter ounce is sufficient. Put them in a warm dry 

 place for a short time and weigh again. They are 

 now lighter than before, having lost some of the 

 water they contain. Place them in a water -bath 

 over a lamp, so that they may be heated to the 

 temperature at which water boils, and leave them 

 there for two or three hours; then remove and weigh 

 again. They are now dried up and will only weigh 



