426 HOOKER'S POSITION AS BOTANIST 



extended the application of such methods to the Himalaya 

 and to Central Asia. He joined with Asa Gray in like enquiries 

 in North America. The latter had already given a scientific 

 explanation of the surprising fact that the plants of the Eastern 

 States resemble more nearly those of China than do those of the 

 Pacific Slope. In resolving these and other problems it was 

 not only the vegetation itself that was studied. The changes 

 of climate in geological time, and of the earth's crust as demon- 

 strated by geologists, formed part of the basis on which he 

 worked. For it is facts such as these which have determined 

 the migration of Floras. And migration, as well as mutability 

 of species, entered into most of his speculations. The Essays 

 of this magnificent series are like pictures painted with a full 

 brush. The boldness and mastery which they show sprang 

 from long discipline and wide experience. 



Finally, the chief results of the Phyto-Geographical work 

 of himself and of others were summed up in the great Address 

 at York. As President of the Geographical Section he chose 

 as his subject * The Geographical Distribution of Organic 

 Beings.' To him it illustrated * the interdependence of those 

 Sciences which the Geographer should study.' It is not enough 

 merely to observe the topography of organisms, but their 

 hypsometrical distribution must also be noted. Further, the 

 changes of area and of altitude in exposed land-surfaces of 

 which geology gives evidence, are essential features in the 

 problem, together with the changes of climate, such as have 

 determined the advance and retrocession of glacial conditions. 

 Having noted these factors, he continued thus : 



With the establishment of the doctrine of orderly evolu- 

 tion of species under known laws I close this list of those 

 recognised principles of the science of geographical distribu- 

 tion, which must guide all who enter upon its pursuit. As 

 Humboldt was its founder, and Forbes its reformer, so we 

 must regard Darwin as its latest and greatest law-giver. 



Now, after thirty years, may we not add to these words of his, 

 that Hooker was himself its greatest exponent ? 



But before all else it was the part which Hooker played in 



