of the Distribution of Arctic Plants, 335^ 



rank of distinct species. Dr. Hooker also enters on the questions 

 aa to the antiquity and migrations of the species of this flora, 

 and the variations which they raay have undergone in the lapse 

 of time. From many of his conclusions on these points, however, 

 geologists who have investigated the posi-pliocene deposits of 

 Europe and America will find themselves obliged to dissent, as 

 well as from the assumption, for it is nothing more, of the unli- 

 mited variation of species in a Darwinian sense, which pervades 

 the paper, notwithstanding the positive geological testimony to 

 the permanence of several of these throughout a great lapse of 

 geological time. We take the following extracts and summaries 

 from an able condensation of the paper by Prof. Gray, in the 

 American Journal of Science : — 



' The immediate subjects of the treatise are the Arctic plants, of 

 every phaenogamous species known to occur spontaneously any- 

 where within the Arctic circle ; the geographical distribution of 

 which, so far as known, is carefully indicated : 1. Within the 

 Arctic region, under the several divisions — Europe, Asia, W. 

 America (Bebring's Straits to the Mackenzie River), E. America 

 (Mackenzie River to Baffin's Bay), and Arctic Greenland. 2. 

 Without this circle, and under the general divisions of N. and 

 Central European and N. Asiatic Distribution, with three lono-i- 

 tudinal subdivisions; American Distribution, with appropriate 

 subdivisions ; S. European and African Distribution ; Central and 

 S. Asiatic Distribution. The theory upon which the facts are 

 collocated and discussed, and which they are thought strongly to 

 confirm, is that of Edward Forbes, which was completed, if not 

 indeed originated by Darwin :* — " first, that the existing Scandi- 

 navian flora is of great antiquity, and that previous to the glacial 

 epoch it was more uniformly distributed over the Polar Zone than 

 it is now ; secondly, that during the advent of the glacial period 

 this Scandinavian vegetation was driven southward in every longi- 

 tude, and even across the tropics into the south temperate zone ; 

 and that, on the succeeding warmth of the present epoch, those 

 species that survived both ascended the mountains of the warmer 

 zones, and also returned northward, accompanied by aborigines of 

 the countries they had invaded during their southern mii^ration. 

 Mr. Darwin shows how aptly such an explanation meets the diflS- 

 culty of accounting for tlie restriction of so many American and 



♦ This is scarcely correct. The theory of distribution originated by 

 Forbes should be distinguished from the extension of it suggested by 

 Darwin. Eds. 



