VI 



THE GEOGRAPHICAL DISTRIBUTION OF 

 PLANTS 



Among all sciences, that of the geographical distribution 

 of animals and plants is necessarily, perhaps, the most inter- 

 national. In crossing the continent of America in order 

 to reach the much beloved far West, my eye was struck by 

 the diversified conditions under which vegetation and agri- 

 culture must thrive. Arid deserts and lofty mountains 

 contrast with humid and fertile plains, with large forests 

 and great rivers, with marshes and lakes. Each of these 

 can, of course, be compared with some parts of Europe, and 

 though the impression we get is that of essential difference, 

 the separate parts are as a fact only a repetition of what is 

 seen with us. 



The cause of the diversity is, therefore, not to be sought 

 in the climatic conditions, but rather in the special character 

 of the vegetation. In American agriculture corn has taken 

 the place which in Europe is given to the smaller cereals. 

 So it is also in nature. Everywhere the European traveler 

 sees new types and new kinds. As a rule they catch his eye 

 by some common features which are strange to him. Among 

 these, I mention only the rich colors of the flowers in sum- 

 mer and of the foliage of trees and shrubs in- the fall. 



We are thus impressed with one of the great principles 

 of the geographical distribution of living organisms. We 

 are convinced that the fundamental difference between the 

 organic beings of the two great continents is not, in the main, 

 due to their climates and soils, but that it can have no other 

 cause than their separate origin from the organisms that 

 peopled them in previous geological times. One of the best 

 proofs of the truth of this principle is given by some of the 



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