Human Factor in Plant Evolution 283 



All but the lowest savages and certain nomad races 

 cultivate some forms of plants for food, but in many 

 cases these have been cultivated from the earliest 

 historic times and have become so altered by culti- 

 vation that their origin is a matter of very great 

 uncertainty. 



It is in the improvement and subsequent changes 

 of the food plants that man's influence as a creator 

 of new plant forms is most clearly seen. The de- 

 velopment of new ornamental plants, except in very 

 recent years, has been relatively unimportant, and 

 practically all of these are clearly traceable to wild 

 ancestors which still exist. Many wild fruits like 

 strawberries, raspberries, crab-apples, etc., have been 

 brought under cultivation but have been altered 

 comparatively little. In some of these cultivated 

 forms it is evident that two or more species have 

 been crossed, and this sometimes makes it difficult 

 to be quite certain as to their origin. Many tropical 

 fruits, such as the mango, mangosteen, cocoanut, 

 durian, custard-apple, and many others, are good 

 botanical species, existing but little changed in the 

 wild state. None of these, however, can be looked 

 upon as the main source of food supply, and perhaps 

 this accounts for the comparatively slight changes 

 that they have undergone in cultivation. The vari- 

 ous fiber plants, like flax, hemp, and cotton, have 

 been but little altered, since the flowers and fruit do 

 not influence in any way the character of the fiber. 

 It is evident that prehistoric man utilized the fiber 



