10 GENERAL BOTANY 



the bread, butter, and meat (which are taken as representative 

 of animal foods) are real organic food materials, which have 

 been previously built up from raw, inorganic materials by 

 green plants. 



Thus, bread, as we all know, is made of flour, which con- 

 sists of finely ground kernels of wheat. The starch and the 

 smaller quantities of nitrogenous gluten of which flour is 

 largely composed were built up, as we have already learned, 

 in the leaves of wheat plants from carbon dioxide, water, 

 and soil salts, absorbed from the air and the soil. After 

 being constructed in the leaves, they were passed into the 

 wheat kernels as reserve food for the growth of the embryos 

 in the seed when the seed should germinate. This ready- 

 made food of the green plant is seized upon by animals for 

 their maintenance. In a similar manner the meat which con- 

 stitutes the food of some animals is ultimately traceable to a 

 plant origin, since even carnivorous animals (meat eaters) derive 

 their food from herbivorous animals (plant eaters). For example, 

 cats live on mice, and the mice get their food from grain or 

 other plant parts ; and cattle, pigs, chickens, and fish, which 

 are the most common sources of meat for man's use, depend 

 upon grass, hay, grain, and water plants for their food supply. 

 All of these animals would starve in a comparatively short time 

 without the continued supply of food which green plants build 

 from carbon dioxide, water, and soil salts. 



This general relation of the lifeless world of matter and 

 force to the living world of animals and plants is illustrated 

 diagrammatically in Fig. 4. It is only necessary to add to 

 the explanation already given the well-known fact that the 

 death of animals and man is frequently caused by colorless 

 plants known as bacteria. Entire crops are also often de- 

 stroyed by parasitic fungi such as the rusts of grains, and all 

 decay is induced by these colorless fungous plants. This decay 

 finally converts the bodies of the dead animals and plants 

 into gases and "other chemical substances, which filter into the 

 soil and form a part of the lifeless matter which is absorbed 

 as raw food material by green plants. The most familiar 



