THE 



AMERICAN NATURALIST 



Vol. XLI April, 1907 No. 484 



THE GEOGRAPHIC DISTRIBUTION OF CLOSELY 

 RELATED SPECIES.^ 



BY ROBERT GREENLEAF LEAVITT. 



The botanical researches of the members of the New England 

 Botanical Club are largely taxonomic and floristic. With some 

 of us this is vocation, with others avocation. The majority per- 

 haps pursue the study of plants in the field and make collections 

 of them in herbaria for their own personal satisfaction. Floristic 

 studies may properly be an end in themselves, whether followed 

 as a business or only for recreation. In the latter case they 

 need no further justification than the fine and pure pleasure they 

 afford to those who love them for themselves. But the results 

 of these studies, for whatever conscious motive pursued, may have 

 an application and a destination far beyond our private aims. 

 Collections of specimens and reports of distribution recorded 

 in accessible journals by well-informed non-professional as well as 

 professional botanists, may help materially in answering some of 

 the largest questions of biological science. In this paper I hope 

 to make it clear that refined taxonomy and most thorough-going 

 plant geography may have a direct relation to the enormously 

 diflScult problem of evolution. 



Organic geography has, indeed, already served the cause of 

 evolution, — in aiding to secure general acceptation of the Descent 

 Theory. Darwin and Wallace, drawing upon the works of tax- 

 onomers, were able to point to features in the distribution of 



• A paper read before the New England Botanical Club at the meeting of 

 Feb. 1, 1907. Published as Contribution from the Ames Botanical Laboratory, 



