420 THE SURVIVAL OF THE UNTJKE. [XXVI 



European type of plum described, of which one hun- 

 dred and twelve, or about two -fifths, were American 

 seedlings. Eighteen varieties cannot be traced, but 

 most of them probably originated in this country. 

 This shows a conspicuous adaptation of the plum to 

 American conditions within a half century. In 1891, 

 this ratio of varieties of American to foreign origin 

 had risen to very nearly one -half for the kinds in 

 actual cultivation, as indicated by the fruit list of 

 the American Pomological Society. This progressive 

 divergence between the two stocks of the common or 

 European species of plum may be expected to pro- 

 ceed until, as in the case of apples (which have 

 received greater attention from our pomologists), 

 we cultivate, almost wholly, varieties of American 

 origin. There is a marked tendency for our pomol- 

 ogy to become independent of its European sources. 

 Even when a promising or valuable foreign variety 

 is introduced, it is found, in the course of a genera- 

 tion or two, that it has strong competitors in its 

 American -grown seedlings. The original causes of 

 this divergence are to be sought in the dissimilar 

 environmental conditions of the Old World and the 

 New World, and not in any direct influence exerted 

 by man. These same differences of environment 

 have, no doubt, been the cause of the separation of 

 the indigenous plums of the tAvo hemispheres into the 

 well-marked specific types which are characteristic of 

 each. In other language, the conditions which have 

 been operating in all past time to separate the types 

 or species of plums in the two continents are now 

 operating upon the imported members of the foreign 

 species themselves ; and from the new forms which 



