194 Asa Gray. 



rather troublesome questions. I can hardly tell you how much 

 your list of alpine plants has interested me." And then Darwin 

 puts more questions to his genial correspondent. 



The long paper, modestly entitled " Statistics of the Flora of 

 the United States," contains numerous tables, comparing as re- 

 gards plants the Northern United States with Europe on one 

 side, and Asia and Japan on the other ; the eastern part of the 

 country with the western, and with the adjoining continents in 

 the north-temperate zone ; the plants of alpine and subalpine 

 regions in the Northern United States, and their distribution 

 southward, and eastward and westward over the other continents ; 

 the distribution of species common to this country and Europe, 

 as to size of orders and genera ; also, as regards related and 

 representative species, and the same for Eastern and Western 

 America ; lists of species of widely sundered habitation ; with 

 numerous other points, and abundant explanatory remarks ; mak- 

 ing thus a thorough philosophical digest of the subject of geo- 

 graphical distribution, having all the completeness as respects 

 the northern United States that the existing state of the science 

 admitted of. He closes with a general review of the. character- 

 istics of the North American flora. 



In the course of the pages, he advocates the idea of a single 

 area of origin for a species, with dispersion at an epoch more .or 

 less ancient, to account for distribution ; sustains Darwin's 

 " surmise " as to the species of large genera having a greater 

 geographical area than those of small genera ; observes that a 

 large percentage of the extra-European types of Eastern Amer- 

 ica are shared with Eastern Asia ; and finds, " that curiously 

 enough, eleven, or one-third of our strictly alpine species com- 

 mon to Europe — all but one of them arctic in the Old World 

 — are not known to cross the Arctic circle on this continent ; 

 so that it seems almost certain that the interchange of alpine 

 species between us and Europe must have taken place in the 

 direction of Newfoundland, Labrador and Greenland, rather 

 than through the polar regions " (xxiii, 73). 



Two years later, in 1859, Dr. Gray had studied a collection 

 of plants from Japan (alluded to in the former paper, xxiii, 

 369, as in hand), which had been collected by Mr. Charles 

 Wright ; and his memoir on the subject, read that year before 



