338 ASA GRAY. 



among scientific men, and, appealing again to the authority of Sir J. D. 

 Hooker, " in point of originality and far-reaching results was its author's 

 opus magnum." In referring to his previous paper in the American 

 Journal, he states with great candor, that, from the facts there brought 

 out, — " 1. that a large percentage of our extra-European types are 

 shared with Eastern Asia ; and 2. that no small part of them are 

 unknown in Western North America," — Mr. Bentham was the first 

 to state the natural conclusion that the interchange between the tem- 

 perate floras even of the western part of the Old World and of the 

 New, has mainly taken place via Asia. He cites Bentham's suggestion 

 of a continuity of territory between America and Asia, " under a lati- 

 tude, or at any rate with a climate, more meridional than would be 

 effected by a junction through the chains of the Aleutian and the 

 Kurile Islands." He then proceeds to show why a connection in a 

 more meridional latitude need not be assumed ; and, fortified by the 

 wide geological knowledge of his friend, Prof. J. D. Dana, he gives 

 a masterly account of the relations of the floras of the North Tem- 

 perate regions from the Cretaceous period to the present time, ac- 

 counting for the present distribution by migrations of species from 

 the- Arctic regions due principally to the different climatic conditions 

 of the jjre-glacial, glacial, and post-glacial eras. The relations of the 

 floras of Eastern America and Eastern Asia was a favorite topic with 

 him, and he often spoke on the subject in public ; his two most impor- 

 tant addresses in which he referred to plant distribution being that on 

 " Sequoia and its History," delivered as retiring President of the 

 American Association for the Advancement of Science in 1872, and a 

 lecture on " Forest Geography and Archaeology," read before the Har- 

 vard Natural History Society in 1878, and afterwards translated in 

 the Annales des Sciences. 



The study of plant distribution necessarily involved the question 

 of the origin of species, and this brings us to a consideration of the 

 relations of Gray to Darwin and Darwinism. Gray first met Darwin 

 at Westbank, the residence of Sir W. J. Hooker at Kew, in 1851 ; and 

 their correspondence dates from a letter of Darwin written April 25, 

 1855, asking for information about the alpine plants of the United 

 States. How intimate and frequent their correspondence became, and 

 how deeply each was interested in the work of the other is admirably 

 shown in the " Life and Letters of Charles Darwin." The published let- 

 ters present a vivid picture of the inner scientific life of these two men, 

 — both equally simple, earnest, remarkably free from prejudice, and 



