262 COOK 



of the Middle West a decade ago, after threatening for a time to 

 become permanently injurious pests, have taken their places as 

 comparatively peaceful settlers among the older plant inhabitants. 



Neotopism is a phenomenon long known in practical agricul- 

 ture, but hitherto not explained and generally not accepted in 

 the scientific world, because the requisite evolutionary viewpoint 

 was lacking. Having come to appreciate the physiological 

 functions of heterism in maintaining the vital efficiency of organ- 

 isms, we are in position to understand that a transfer to new 

 conditions may also act as a direct stimulant of organic vigor, 

 an artificial symbasis, as it were, which has probably contrib- 

 uted much to the sustained vitality of our inbred cultivated 

 plants. 



Likewise the heterism of the species might be thought of as 

 increased by the extension to the new locality, and the added 

 neotopic diversity might serve the same purpose as normal 

 heterism in helping to maintain the organic vigor of the species 

 as a whole, under conditions of free interbreeding. Thus devices 

 for securing wide distribution serve the interests of the species 

 in a variety of ways. They not only tend to increase the 

 numerical prosperity of the group, but increase the facilities 

 for interbreeding among the members of the species and also 

 give it the benefit of as widely different conditions as possible. 

 The diversity of conditions accentuates diversity of descent and 

 thus contributes to the vigor of the species. With sedentary 

 plants in particular we should be prepared to learn that changes 

 of conditions of growth are as beneficial as changes of diet for 

 man and the higher animals. 



In many crops it has become a regular agricultural practice 

 to exchange seed between more or less distant localities. Seed 

 planted in a new locality often produces better and more fertile 

 plants than in the place where it was grown, and better than 

 the same stock after it has been planted in the same place for a 

 series of years. The new conditions afford, for a time, the 

 same physiological benefits as diversity of descent and new 

 variations, and constitute, indeed, a striking confirmation of the 

 physiological relations of these groups of phenomena. 



In many other cases neotopism may only bring to the surface 



