CHAPTER XII 

 THE FOOD OF PLANTS 



Three frequently used words will help us arrive at an understanding of 

 the nature of food. Thev are: starvation, desiccation, and suffocation. 

 Suffocation implies a lack of oxygen; desiccation, a deficient water con- 

 tent of the body; and starvation, a lack of food. More recently "mineral 

 deficiency" has become a common expression among physicians to denote 

 an inadequate supply of certain mineral salt ions. Botanists have found 

 these four expressions of bodily needs — mineral deficiency, suffocation, 

 desiccation, and starvation — equally pertinent in distinguishing the salt, 

 oxygen, water, and food relations of plants. 



Sources of foods. The fact that cattle, dogs, birds, insects, and other 

 animals secure food either by eating plants, by eating animals that feed 

 on plants, or by eating commercial products obtained from plants, needs 

 no further evidence. Equally commonplace is the admonition that to 

 prevent the decay of food, the infection of wounds, and the spread of 

 certain diseases, it is necessarv to avoid, or to destroy by antiseptics, 

 certain non-green plants known as bacteria and fungi. Non-green plants, 

 like animals, obtain food from other plants or from animals, or from 

 plant and animal products. The green plants therefore appear to be 

 unique among organisms in not securing their food from other organisms 

 or from the products of other organisms. Evidently animals and non- 

 green plants depend upon an external source of food; green plants do not. 



Aristotle's notions about plant foods. Twenty -three hundred years ago 

 the philosopher Aristotle, speculating on the ways of nature, concluded 

 that green plants obtain food from the soil. Reasoning by analogy from 

 his observations of animals, he concluded that the source of food of any 

 organism lies outside its own body. Since many green plants have parts 

 of their bodies in the soil, he thought that they must receive food from 

 that source. He had no basis for reaching a better conclusion regarding 

 the food of green plants because ver)' little was known about their 

 physiology. The chemistry of the inorganic world also was largely a 

 mystery at that time. Only a few of the metallic elements had been iden- 

 tified; and more than 20 centuries passed before oxygen, hydrogen, 



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