168 Fernald — Helationships of some American 



early students of the group various European and American 

 species were considered essentially identical ; but among recent 

 authors there has been an increasing tendency to regard nearly 

 all American forms as endemic, and to maintain as organically 

 distinct trees growing, for instance, on the American and 

 the Asian sides of Behring Sea. 



That there is not only a strong similarity, but a marked pro- 

 portion of identity, in the herbaceous floras of the circumboreal 

 regions has long been recognized ; and, although the tendency 

 to ignore this almost axiomatic truth has been conspicuous in 

 the work of certain American as well as European botanists, the 

 increasing evidence of its validity has forced itself upon the 

 attention of others. This similarity in the boreal floras of the 

 eastern and western hemis^Dheres was very emphatically pointed 

 out by Sir Joseph Hooker in his discussion of the Distribution 

 of Arctic Plants.* Although our knowledge of the distribution 

 and relationships of plants has very greatly increased since 

 Hooker's tabulation was made, his outlines still furnish an 

 approximately accurate basis for generalizations. If we con- 

 sider the boreal" distribution of some well-known northern 

 genera whose species were then clearly interpreted, we shall 

 find that of the 61 Arctic species of Carex recognized by 

 Erancis Boott, 58 extend southward into temperate Europe, 51 

 into temperate America, and 43 into temperate Asia ; of the 

 16 Arctic Junci recognized by Hooker all 16 extend into 

 temperate Europe, 15 into temperate America, and 14 into 

 temperate Asia; of Hooker's 24 Arctic species of Saxifraga, 

 19 extend into temperate America, 17 into temperate Euroj)e, 

 and 14 into temperate Asia. This estimate is altered from 

 that of Hooker only in so far as recent data has been immedi- 

 ately accessible to the writer ; but it does not, of course, take 

 into account such well-known species as Carex rijparia^ C. 

 Pseudo- Cyperus^ Juncus temds^ etc., which occur in temperate 

 regions oF both hemispheres, though not within the Arctic 

 Circle, but which, if counted, would increase the number of 

 identical species in the eastern and western hemispheres. 



Toward the warmer regions of each continent the number 

 of identical plants rapidly diminishes, and the proportion of 

 endemic species becomes very great. But in view of the 

 marked similarity of the herbaceous vegetation of northern 

 Europe, Asia and North America, it seems only logical to ex- 

 pect a notable proportion of identities between the trees and 

 shrubs of boreal range, especially when, as iwBetula and Sa.lix, 

 several species extend nearly or quite to the northern limits of 



* J. D. Hooker, Trans. Linn. Soc, xxiii, pt. 2, 251-358; see also Gray, 

 Mem. Am. Acad., n. s., vi, 377-449, and extract ''Flora of Japan," in Sci. 

 Pap. of A. Gray, selected by C. S. Sargent, ii, 124-141. 



