How the Plant Increases Its Substance 31 



formed by burning of plant or animal bodies, and retain 

 the carbon, the oxygen being set free. But this oxygen- 

 izing power of plants is much less than is generally 

 supposed; for the respiratory process of plants, giving 

 out carbon dioxid partially counteracts the effect of 

 the assimilative process. Carbon assimilation does not 

 take place rapidly in a subdued light, such as exists 

 in an inclosed room. 



50. Importance of Carbon Assimilation. With one 

 or two minor exceptions, this process of food-making 

 is the only known means of increasing the supply of 

 food for both plants and animals. We can now answer 

 the question asked in U 38. By this process the corn 

 plant is able to reproduce itself many fold and, also, 

 " tall oaks from little acorns grow." No animal has 

 this power to form food substances from the simpler 

 compounds. It is plain, therefore, that the farmer's 

 stock, and indeed all life, is dependent upon plant life 

 for food. More than one-half of everything grown on 

 the farm is carbon drawn from the air. 



QUESTIONS 



1. Why are most leaves flat? 2. Describe the layers in a leaf. 

 3. Which layer manufactures food? 4. Describe carefully how the 

 carbon of the air gets into the leaf. 5. Is light necessary for the 

 formation of the green color in leaves? 6. What is the effect of 

 continued darkness on green plants? 7. Name the five necessary 

 conditions for the making of plant substance. 8. Discuss the 

 importance of food-making by plants. 



