THE 



AMERICAN NATURALIST 



Vol. LIV. September- October, 1920 No. 634 



STEXOTIIKRMY AND ZOXK INVASION' 1 



The conception of geographical distribution seems to 

 have come to the botanists of the later fifteenth and ear- 

 lier portions of the sixteenth centuries as a distinct and 

 gradually developing idea. They began to realize that 

 the plants of central and northern Kurope were different 

 from those of Greece and Italy as treated of by Theo- 

 phrastus and his successors and were worthy of study 

 for their own sakes. With the revival of learning, the 

 discovery of the "New World" and the attention paid 

 to the plants and animals of the different countries being 

 made known through the visits of the various voyagers, 

 both the knowledge of the different countries and that of 

 the natural objects brought back from them emphasized 

 more and more the idea of geographical differences in 

 flora and fauna and the gradual perception that there 

 might be some general laws or principles governing 

 them. It remained for Humboldt in a series of papers in 

 1805, 1807, 1816, 1817 and 1820, to place the matter of 

 the geographical distribution of plants on a firm scientific 

 basis. After Humboldt's preliminary work, came the 

 studies of a number of leading botanists and gradually 

 there have arisen various points of view, especially as to 

 factors concerned and as to the division of the subject 

 into various categories according to the special factor, or 

 set of factors, emphasized. The studies in ecology, which 

 have come more recently to represent the activities 



•al Club, New York City, de- 



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