HOW PLANTS GROW 65 



subject them to all sorts of conditions, but no starch 

 results. No chemist, however skillful, has ever suc- 



! in making starch. But the simplest little plant 

 that arrows knows the process, and even day in spring 

 and rammer, when the sun shines, is husy producing this 

 useful substance. The chlorophyll in the green leave* 

 of plants is the starch manufacturer, the leaf is the fac- 



and Bunlighl its power. When the waves of -un- 

 tight strike on the surface of green haves the chloro- 

 phyll is busy converting water and carbon dioxide into 

 Btarch j when the sunsliine ceases the chlorophyll stops 

 work. But starch is not the only substance that is 

 formed in plants. Sugar, oil, woody matter, protein, 

 and various other compounds are likewise formed in 

 the plant No one knows exactly how these various 

 compounds an- formed in the plant, hut it is tery pro- 



btble that most of them are formed in the leaf under 

 the influence of sunshine. The various carbohydrates 

 are probably made from starch. The protein com- 

 pounds besides carbon, hydrogen and oxygen, contain 

 nitrogen and sulphur, which dementi are drawn from 

 <>il. But as to just how they are made into the 

 various compound- found in plants we do not at pi 

 know. 



66. Sap and Its Work. — The compounds formed in 

 the leaves of plant- are distributed by the sap to various 

 parts of the plant n re needed to build it up. As 



the plant grows older it> various parts change in compo- 

 sition. The stems of most young plants contain starch, 

 sugar, and nitrogenous substances, which, as the plant 

 5 



