CHAPTER XXVI 

 UTILIZATION OF FOOD IN THE PLANT 



266. Need of food in the plant. In the discussion of the 

 manufacture of food there has been no mention *of the use 

 made of the food by the plant. People generally give so little 

 thought to the need which a plant has for carbohydrates, fats, 

 and proteins that we frequently speak as if the foods were 

 made for us. This is not the truth. A plant has need for 

 food, as we have, and in addition it has the power of making 

 its food supply from such simple substances as carbon dioxide, 

 water, and other compounds. If a plant is not interfered 

 with, the food which it manufactures is commonly used by it 

 and for its own purposes. For instance, a part of our food is 

 composed of starch from wheat grains, but if the wheat had 

 not been disturbed, the grains would have fallen to the ground, 

 where under favorable conditions they would have started to 

 grow into new wheat plants. These young plants would have 

 used the food that was stored up in the grain. By harvesting, 

 milling, baking, and eating the wheat we have appropriated 

 for our own purposes that which otherwise would have fed a 

 young wheat plant. 



There are several purposes for which food is used in the 

 plant. We have already spoken of one in the section on 

 respiration. It will be recalled that when the living substance 

 is destroyed in the process of freeing energy, the loss must be 

 made good by a supply of new material. It is the food that 

 supplies this new material. New material is needed not only 

 to replenish waste but also for the growth of plants. Both 

 the living protoplasm and the cell walls must be built up 

 from food materials. 



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