206 THE GENESIS AND MIGRATIONS OF PLANTS 



The earliest suggestion on this subject known to the writer 

 is that of my old and dear friend, Professor 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 

 new facts disclosed by Heer and Lesquereux, Gray returned 

 to the subject in 1872, and more fully developed this conclu- 

 sion with reference to the Tertiary floras, 1 and still later he 

 further discussed these questions in an able lecture on " Forest 

 Geography and Archaeology." 2 In this he puts the case so 

 well and tersely that I may quote the following sentences as a 

 text for what follows : 



" I can only say, at large, that the same species (of Tertiary 

 fossil plants) have been found all round the world ; that the 

 richest and most extensive finds are in Greenland ; that they 

 comprise most of the sorts which I have spoken of, as Ameri- 

 can trees which once lived in Europe Magnolias, Sassafras, 

 Hickories, Gum-trees, our identical Southern Cypress (for all 

 we can see of difference), and especially Sequoias, not only the 

 two which obviously answer to the two Big-trees now peculiar 

 to California, but several others ; that they equally comprise 

 trees now peculiar to Japan and China three kinds of Gingko- 

 trees, for instance, one of them not evidently distinguishable 

 from the Japan species which alone survives ; that we have 

 evidence, not merely of Pines and Maples, Poplars, Birches, 

 Lindens, and whatever else characterize the temperate-zone 

 forests of our era, but also of particular species of these, so 

 like those of our own time and country, that we may fairly 

 reckon them as the ancestors of several of ours. Long 

 genealogies always deal more or less in conjecture ; but we 

 appear to be within the limits of scientific inference when we 

 announce that our existing temperate trees came from the 

 north, and within the bounds of high probability when we 



1 Address to American Association. 



* American Journal of Science, xvi., 1878. 



