THE PURPLE SAXIFRAGE 89 



could wish, if it suits my rivals worse than it suits me. 

 Some plants which take up little room I don't strongly 

 object to as neighbours. Sedums and pinks and the 

 modest little Drabas are unobjectionable. Polemoniums 

 are too aggressive, and cover too much ground with their 

 odious blue flowers. How any one can dress in blue I 

 can't understand ! Cryptogamic riff-raff, such as lichens 

 and that sort of thing, need not be taken into account. 

 But whatever you do, keep me off the places where there 

 are a lot of heaths. I am quite sure that the heaths and 

 I can never be happy together." 



Some naturalists, whose opinion carries the greatest 

 weight, have invoked the Glacial Period to explain the 

 distribution of such plants as the purple saxifrage. Charles 

 Darwin and Edward Forbes put forth a glacial explanation 

 of the present range of arctic and alpine plants, which was 

 afterwards adopted by Sir Joseph Hooker in his " Outlines 

 of the distribution of Arctic plants." l The leading 

 features of the explanation are these : In glacial times 

 the ancient flora of Europe, whatever it was, became sup- 

 planted by an arctic flora. When the climate grew 

 milder again, the arctic flora either retreated northwards, 

 or else climbed the alps and other mountain ranges. In 

 this way it came about that the same plants occur on 

 distant mountain summits and also in the arctic regions. 



Analysing the argument, it seems to rest upon these 

 four propositions : 



1. The arctic regions have a characteristic flora. 



2. The alpine regions of Europe have a characteristic 

 flora. 



3. These two floras are so nearly the same that they 

 may be supposed to have had a common origin in com- 

 paratively recent times. 



4. The arctic- alpine flora in central Europe is now 

 restricted to high ground. 



I believe on the contrary that known facts and even 



1 Phil. Trans., 1860. 



