10 



collected their botanical treasures, phaenogamic and cryptogamic, 

 you would perceive that the flora of each was so similar in its 

 main features, as clearly to betray a common origin and similar 

 mode of distribution. What then was this origin, and when did 

 it take place, in what manner was this dissemination over distinct 

 mountain ranges effected, are the two correlative problems which 

 we have to solve. And in arriving at a correct solution, it will 

 materially assist us to compare our boreal flora with that of other 

 northern countries. Suppose you had made a complete collec- 

 tion of British Alpine plants and written out a catalogue of their 

 names. On comparing this with a like catalogue of those of 

 other alpine regions, you would find that there was a greater 

 similarity between it and that of Scandinavia than of any other 

 country on the globe. In fact, but for the circumstance that the 

 Scandinavian list possesses a greater number of species belong- 

 ing to a strictly Arctic type, not found in Britain, as might be 

 expected, the two would be quite identical. Whence then this 

 similarity in the floras of two countries, far separated from each 

 other by the waters of the German Ocean ? Is it that plants 

 were originally distributed by haphazard over the world, and 

 that they grow indiscriminately wherever there is a soil and 

 climate suitable for their different natures ? The whole experience 

 of Botanical Geographers is against such a crude supposition, 

 which has long ago been sufficiently exploded. We must, there- 

 fore, account for it in some other way, and on some more 

 scientific principles. 



The key to the solution of the problem is undoubtedly 

 to be found in the now almost universally recognised doctrine of 

 " Specific Centres," that is, of certain geographical points from 

 which different types of plants have radiated. Such a doctrine, 

 apart from any other considerations whatever, seems to be 

 necessitated by the fact to which Mons. De Candolle alludes in 

 his essay on Botanical Geography, though he does not carry out 



