Asa Gray, 195 ' 



the American Academy of Arts and Sciences, closes with a 

 sequel to the subject of Geographical Distribution, bringing 

 out conclusions of still higher interest. He starts off with the 

 then new announcement and its evidence, that, among the 

 plants of Japan, more species are represented in Europe 

 than over the nearer land,, western North America ; more in 

 eastern North America than in either of the other two regions ; 

 and adds, that hence, there has been a peculiar intermingling of 

 the eastern American and eastern Asia floras, which demands ex- 

 planation. The explanation he finds in the idea of migrations 

 to and from the arctic regions, determined in part, at least, by 

 the climate of the preglacial, glacial and postglacial eras ; and 

 that the alpine plants of the summits of the White Mountains, 

 Adirondacks, Black Mountains and Alleghanies, are species left 

 by the retreating glacier. 



Dr. Gray returned to this subject in his presidential address, 

 in 1872, before the American Association for the Advancement 

 of Science,* and, owing to the progress that had been made in 

 the paleontology of the continent, the arctic portion as well as 

 the more southern, and developments elsewhere also, he was 

 enabled to trace out the courses of the migrations of plants, the 

 Sequoias or Redwoods and many other kinds, by positive facts 

 with regard to the arctic and more southern floras ; and showed 

 that the distribution southward into the western United States, 

 into eastern Europe or western Eurasia, and into Japan and Asia 

 or eastern Eurasia, was not only dependent, as he had before put 

 forth, on change in continental climates, but also that the par- 

 ticular direction southward was determined to a large extent 

 by fitness of climate as to heat and dryness. The surprising 

 revelations are now so generally known that this brief reference 

 to them is all that is here needed. 



Gray's comprehensive knowledge of the plants of the world, 

 of their distribution, and specifically of the relations of North 

 American species, genera and orders to those of the other con- 

 tinents, and the precision of his knowledge, enabled him to be 

 of much service to Darwin in the preparation of the first edi- 

 tion of the Origin of Species, and afterward, also, in the elab- 



* This Journal, III, iv, 282, 1872. 



