98 STATE HORTICULTURAL SOCIETY. 



consin and Minnesota into the territory beyond the national boundary. 

 It thus becomes a conspicuous member of that more comprehensive flora 

 belonging to the Atlantic states and the region of the great lakes. Fur- 

 thermore, what is true of the white pine is true also of very many other 

 species that go to make up our flora. They belong not to Michigan 

 exclusively, but to the wider region of eastern North America. Through- 

 out this great area the vegetation, in its broad features, is essentially the 

 same. The forest trees of Michigan and Wisconsin are, in general, iden- 

 tical with those of New York and New England, Pennsylvania, Virginia, 

 and Canada. The beech, maple, and basswood, oak, hickory, and horn- 

 beam, willows and ashes and walnuts, and a long list of other familiar 

 trees and shrubs, with a still longer list of herbaceous plants, have 

 stamped upon this whole region its well-known and characteristic features. 



As previously intimated, a relationship similar to that already noticed 

 between the Michigan flora and that of the remaining lake and Atlantic 

 states, may be traced between the latter and the vegetation of a much, 

 wider region extending far beyond the limits of the American continent 

 Similar, but not quite identical; for, while a given Michigan plant has 

 precisely the same botanical character in whatever part of the eastern 

 United States it may occur, outside of this region, particularly beyond 

 continental limits, such an identity of specific characters may or may not 

 be retained. To recur to the plant that has already served as an illustra- 

 tion, the white pine of Michigan is everywhere, in eastern North America, 

 the same species, identical in every specific feature, and hai'dly manifesting 

 variation enough to aflford ground for the varieties that have sometimes 

 been assumed to exist. Beyond the limits of the continent the white pine 

 is not indigenous. It is represented, however, in southern Europe, by the 

 Cembrian pine, Pinus Cembra, L., and in southern Asia by the Bhotan 

 pine, Pinus excelsa, Wall, species that resemble it so plainly as to at once 

 suggest close relationship, and yet readily distinguishable by characters 

 that are generally admitted to be of specific value. There is a peculiar 

 interest attaching to these related forms, so like and yet so plainly diif erent, 

 as if challenging the botanical expert to point out marks by which they 

 are to be distinguished from their new world congeners, and to tell, if he 

 can, how they came to be growing so far from them and from each other. 

 This is but a single case out of very many. We often find, on the moun- 

 tains of the Scandinavian peninsula, or further east in northern Siberia, 

 and with remarkable frequency in Japan and eastern Asia, plants either 

 absolutely identical with our own or closely related to them. 



The reason for this peculiar distribution of related or identical forms, 

 as pointed out by Professor Gray many years ago, it is to be sought in the 

 geological history of the northern hemisphere. During the so-called glacial 

 period the plants of Greenland and northern Europe and Asia were driven 

 southward by the cold to flourish for a time in lower latitudes, retreating 

 again to the north with the return of a warmer climate, but leaving here 

 and'there, in secluded swamps or in the cold recesses of the mountains, on 

 either side of the globe, a representative to tell the story of migrations more 

 ancient and escapes more thrilling than those of Trojan or Viking. 



Of our own Michigan plants, a very considerable number have apparently 

 had just such a history. They range far northward into Labrador and 

 still higher latitudes, where they are quite as much, perhaps more, at home 

 than they are with us, and several occur as identical or closely related 

 species in eastern Asia. 



