CHAPTEK VIII. 



GENERAL LAWS OF ORIGIN AND MIGRATIONS OF PLANTS. 

 — RELATIONS OF RECENT AND FOSSIL FLORAS. 



The origination of the successive floras which have 

 occupied the northern hemisphere in geological time, 

 not, as one might at first sight suppose, in the sunny 

 climes of the south, but under the arctic skies, is a fact 

 long known or suspected. It is proved by the occurrence 

 of fossil plants in Greenland, in Spitzbergen, and in Grin- 

 nell Land, under circumstances which show that these 

 were their primal homes. The fact bristles with physical 

 difficulties, yet is fertile of the most interesting theoreti- 

 cal deductions, to reach which we may well be content to 

 wade through some intricate questions. Though not at 

 all a new fact, its full significance seems only recently to 

 have dawned on the minds of geologists, and within the 

 last few years it has produced a number of memoirs and 

 addresses to learned societies, besides many less formal 

 notices.* 



The earliest suggestion on the subject known to the 

 writer is that of Prof. Asa Gray, in 1867, with reference 

 to the probable northern source of the related floras of 

 North America and eastern Asia. With the aid of the 

 new facts disclosed by Heer and Lesquereux, Gray re- 



* Saporta, a Ancienne Vegetation Polaire"; Hooker, " Presidential 

 Address to Royal Society," 1878 ; Thistleton Dyer, " Lecture on Plant 

 Distribution"; Mr. Starkie Gardner, "Letters in 1 Nature,'" 1878, &c. 

 The basis of most of these brochures is to be found in Heer's " Flora 

 Fossilis Arctica." 



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