ioo Field, Forest, and Wayside Flowers 



But green plants make their own food. The 

 chlorophyll which they contain is a lure to catch 

 the sunbeams, which, when caught, are set to 

 work to help the protoplasm in the work of food- 

 and tissue-building. 



This work can prosper only under certain con- 

 ditions. Sunshine must fall upon the plant, car- 

 bon dioxide gas must be mingled with the air 

 which surrounds it, the temperature must not be 

 too low, and water must come up from the roots 

 into the leaves and green stems. Under these 

 circumstances food-making goes merrily on. 



The first evident product of the plant's industry 

 is starch. This is a much less complex substance 

 than the proteids, for it contains but three ele- 

 ments, carbon, hydrogen, and oxygen, and they 

 are mingled in accurately known and unvarying 

 proportions. 



The carbon comes out of the carbon dioxide 

 which the leaves breath in ; the hydrogen is a 

 chemical constituent of the water which the roots 

 suck up, and the oxygen comes in as the other 

 element of the water, or is inhaled from the at- 

 mosphere by the green stems and the foliage. 



Some surplus oxygen is left after the starch- 

 making, and this is exhaled by the leaves. When 



