288 Plant Life and Evolution 



vated plants have crowded in hordes of less welcome 

 immigrants, the troops of foreign weeds which have 

 taken possession of all the waste places along the 

 roadsides, fence corners, and other places not 

 monopolized by the crops. Most of the more ag- 

 gressive weeds, thistles, dandelions, burdocks, sor- 

 rel, etc., are of European origin, these hardy in- 

 vaders ousting the delicate shade-loving native 

 plants which thrive only in the shelter of the dense 

 forest. Only in the swamps and other similar open 

 places do the native plants hold their own against 

 the foreign invaders. . . . 



Introduced Plants. It not infrequently happens 

 that plants escape from cultivation and find them- 

 selves so much at home that they have all the ap- 

 pearances of natives, and this has led to many er- 

 rors in determining the origin of many cultivated 

 species. Thus the orange grows spontaneously in 

 the forests in Florida and Jamaica, and is to all 

 appearances wild, but we know that it is a native 

 of the Old World and was unknown in America be- 

 fore the advent of the Spaniards. The banana 

 also is often met with in the forests of nearly all 

 tropical countries, but there is no question that it is 

 an escape from cultivation, and the same is true 

 undoubtedly of many other tropical fruits, like the 

 mango and guava. The readiness with which culti- 

 vated plants adapt themselves to their new homes, 

 makes the discovery of their real origin often a 

 matter of very great difficulty. 



