CHAPTER I 

 INTRODUCTION 



1. The use of plants. In Part I a brief account of the 

 structure of plants and of their principal activities is given. 

 This forms the basis of the science of Botany and develops 

 some knowledge of a very conspicuous part of nature. But 

 there is another aspect of plants, which does not deal with 

 them as a source of knowledge, but as things of great use. 

 Comparatively few people are interested in knowing about 

 plants, but every one is interested in using plants. 



When one recalls the uses made of plants, he realizes that 

 the human race is very dependent upon them. Of all the 

 uses to which plants are put, however, the most conspicuous 

 is their use as a source of food. In fact, even the meat we 

 use is obtained from animals that feed upon plants ; so that, 

 directly or indirectly, all food is derived from plants. It is 

 evident that this must be true, because, as was stated in 

 Part I, green plants are the only living things that can manu- 

 facture food out of raw materials ; that is, materials that are 

 not food. It is upon this food manufacture that all plants 

 and animals depend; the green plants use the food they 

 manufacture for themselves, while plants that are not green 

 (as mushrooms) and all animals depend upon the food that 

 green plants manufacture in excess of their own need. 



The most primitive men, of course, as they roamed about, 

 obtained their plant food from wild plants. Even yet there 

 is much " wild food " used, notably such berries as black- 

 berries, raspberries, huckleberries, etc. An important stage 

 in the progress of the human race was when men began to 

 select certain of the wild plants for cultivation. The rais- 



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