94 



PLANTS MAKE FOOD 



Protein food is present in the leaf, and is found in the stem or root 

 as well. Proteins can apparently be manufactured in any of the 

 cells of green plants, the presence of light not seeming to be a nec- 

 essary factor. How it is manufactured is a matter of conjecture. 

 The minerals brought up in the soil water form part of its composi- 

 tion, and starch or grape sugar give three elements (C, H, and 0). 

 The element nitrogen is taken up by the roots as a nitrate (nitrogen 

 in combination with lime or potash). Proteins are probably not 



made directly into protoplasm 

 in the leaf, but are stored by 

 the cells of the plant and used 

 when needed, either to form 

 new cells in growth or to re- 

 pair waste. While plants and 

 animals obtain their food in 

 different ways, they probably 

 make it into living substance 

 {assimilate it) in exactly the 

 same manner. 



Foods serve exactly the same 

 purposes in plants and in ani- 

 mals ; they either build living 

 matter or they are burned 

 (oxidized) to furnish energy 

 (power to do work). If you 

 doubt that a plant exerts 

 energy, note how the roots of 

 a tree bore their way through 

 the hardest soil, and how stems or roots of trees often split open 

 the hardest rocks, as illustrated in the figure above. 



Starch-Making and its Relation to Human Welfare. — Leaves 

 which have been in darkness show starch to be present soon after 

 exposure to light. A corn plant sends 10 to 15 grams of reserve 

 material into the ears in a single day. The formation of fruit, and 

 especially the growth of the grain fields, show the economic im- 

 portance of this fact. Not only do plants make their own food 

 and store it away, but they make food for animals as well. And 



An example of how a tree may exert 

 energy. This rock has been split by 

 the growing tree. 



