592 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1918. 



The great botanists preceding Hooker had believed in the " special 

 creation" of this endless variety of species and widely differing 

 grades and elaboration of vegetable life, as an ultimate fact. Buffon, 

 at the end of the eighteenth century, had pointed out the connection 

 of climate with the distribution of plants, and argued that vegetation 

 must have commenced where the cooling globe was first cold enough 

 to support it, — i. e., at a pole. He remarks that "the same tempera- 

 ture might have been expected, all other circumstances being equal, 

 to produce the same beings in different parts of the globe both in the 

 animal and vegetable kingdoms." To him also we owe the recogni- 

 tion of the limitation of groups of species to regions separated from 

 one another by "natural barriers." Tournefort had, still earlier, 

 pointed out the likeness between the vegetation of successive eleva- 

 tions, implying successive reduction of temperature, and that of suc- 

 cessive degrees of latitude carrying the same successive change of 

 climatic condition. Humboldt (whom Hooker met in Paris in 1845) 

 showed that many great natural orders of plants (Gramineae, Le- 

 guminosae. Compositae, etc.) are subject to certain laws of increase 

 or decrease relatively to other plants in going polewards (in both 

 hemispheres) and skywards. The construction of' the "isothermals" 

 of the globe, which we owe to Humboldt, was a great instrument 

 toward the advancement of geographical botany. Hooker regarded 

 him (as he says in a letter to Darwin in 1881) as the greatest of 

 scientific travelers; and in 1815 he writes of him (vol. i, p. 185) : 



He was never tired of coming to ask me questions about my voyages I the 

 Antarctic expedition with Ross] ; he certainly is still a most wonderful man, 

 with a sagacity and memory and capability for generalizing that are quite 

 marvelous. 



Lyell had shown that distribution is not a thing of the present 

 only or of the present condition of climates and present outline and 

 contours of lands. He also showed that our continents and oceans 

 had experienced great changes of surface and climate since the in- 

 troduction of the existing assemblages of plants and animals; that 

 there had been a glacial period, and long before that a warm Arctic 

 period, as proved by the abundant fossils (brought back by Arctic 

 travelers) of plants belonging to a warm temperate zone. But these 

 relations of flora and climate were looked upon as the outcome of 

 direct adaptation by sudden and inexplicable acts of creation. It was 

 Hooker's special merit and privilege to be the first to introduce into 

 the attempt to explain the facts of the geographical distribution of 

 plants, the conceptions already current in the scientific world of (a) 

 the mutability and derivative origin of species; and (b) the mig ra- 

 tion of floras. This he did independently, by his own "self- 

 thought," as Darwin termed it. His views are apparent in his earlier 



