THE LEAVES 61 



sorbs these rays, and the energy derived from them 

 enables protoplasm to carry on the work of food- 

 making. 



69. The leaf is a machine or a mill. If the ac- 

 tivity of chlorophyl might be described in another 

 way, it could be said that the leaf is an engine. The 

 chlorophyl would be the boiler, and when light falls 

 upon it energy or power is set free, which causes 

 the engine to move or perform work, as when heat 

 is applied to the boiler of a steam engine. The leaf 

 is a solar engine and gets its energy from light 

 instead of heat rays. The power acquired from light 

 by chlorophyl drives the protoplasmic machinery and 

 enables it to take water and carbon dioxide and 

 make sugar from them, throwing off certain things 

 not used in the process. After the formation of 

 sugar it is combined with nitrogen and other ele- 

 ments before it can become a part of the living 

 matter. 



70. Quality of light most useful to the plant. 

 Prepare two boxes of seedlings. The boxes should 

 be at least six or eight inches deep, and the plants 

 should be grown in a thin layer of soil at the bot- 

 tom of the box. Cover one box with a sheet of win- 



