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TEXTBOOK OF BOTANY 



plants in the world each year is probably in the neighborhood of 8-10 

 times the amount liberated by the animals in the world during the same 

 time. A corn plant, for instance, oxidizes about one-fourth of the food it 

 makes. One-half of the food it makes is converted into fibers (cellulose, 

 wood, cutin, etc.) which are indigestible by the enzymes of animals. 

 They may, however, be digested and used as food by certain special 

 groups of bacteria and fungi. The fibers that are not digested by these 

 non-green plants become the humus of the soil. Onlv about one-fourth of 

 the food made by the com plant accumulates, part of which becomes 

 available to animals." 



Food per acre in terms of available energy. With a knowledge of respi- 

 ration as a background we may compare the amount of food harvested 

 per acre on the basis of Calories of energy. In Table 4 a summary is given 

 of the average yield per acre, its food value calculated in Calories, and 

 tlie number of men that can be fed for one day by the different crops 

 harvested from one acre, assuming that each man requires 3000 Calories 

 per day. 



Table 4. Energy Content of Food Products from an Average Acre 



If the grain from an average acre of corn is fed to beef cattle, the 

 dressed beef produced amounts to only 125 pounds and yields energy 

 equivalent to the food of 43 men for one day, a loss of 95.7 per cent of 



- There is a possible error in this comparison, namely, there are many bacteria in tlie 

 alimentary tracts of animals that may digest the cell walls of plants. Some of the products 

 of these digestions pass into the cells of the animal. Some of the wood-boring beetles 

 have fungi in their intestines that digest cellulose, and the beetle's food is the resulting 

 sugars and other end products. 



