THE INTER-RELATIONS OF PLANTS AND MAN 117 



cycle; because of this, medical and bacteriological sciences have 

 come to be important human activities. 



However, man has formed other relationships with plants, as 

 a result of his civilized mode of existence. Rather than becoming 

 more independent of these green allies, he has increased his 

 dependence upon them, and is beginning to realize that they can 

 be merciless foes as well as helpful friends. A few of these rela- 

 tionships will be suggested in the balance of the chapter. 



Plant Relations Beneficial to Man 



Many of the ways in which plants are of importance in the 

 lives of animals have been elaborated upon an extensive scale by 

 man, with an exploitation of those species possessing useful char- 

 acters. At the same time new relationships, resulting from the 

 demands of civilization, have developed which make our de- 

 pendence upon plant life even greater than that of many animals. 



Still most important of these is man's reliance upon plants as a 

 basic source of food. By a slow and at times costly method of 

 trial and error, man learned which plants were fit to eat and 

 which parts of the plant were most edible. After the existence of 

 certain food plants became common knowledge, man evolved 

 methods of growing these near to where he lived instead of de- 

 pending upon their chance occurrence in nature. The story of the 

 origin and domestication of food plants is one of the most 

 fascinating episodes in the conquest of our environment. With the 

 advent of agriculture, man could cease his daily search for food 

 and settle down to more civilized tasks. This dependence upon 

 plants extended to his domesticated animals which he used for 

 food or as beasts of burden. The presence of good grazing areas, 

 therefore, was almost as important to him as his own food 

 plants. 



The thallus members of the plant kingdom have never been 

 of importance as food for man. We have seen that some of the red 

 seaweeds are eaten in various countries, notably the British Isles 

 and Japan; but for the most part the phyla of the Green, Red and 

 Brown Algae are of little value in this respect. The fungi are 

 better known as food plants; though mushrooms can claim the 

 distinction of being edible plants more because of their unusual 



