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PLANTS ON THE SOUTH SIDE OF THE ALPS. 121 



Congress held at Plorence in 1874. Tlic title is ** Sur les causes de I'in^gale distribution 

 des plantes rares sur la cliaine des Alpes." * It is worthy of notice that M. de Candolle 

 places as a text at the head of his paper the followini]i; quotation from Mr. Ball : — " It is 

 a matter of curious inquiry to ascertain why certain districts of the Alps possess a far 

 more varied vegetation than others." 



I must admit that the explanation offered by M. de Candolle has always seemed to 

 me extremely probable, and indeed almost convincing. Mr. Ball, who opened the 

 discussion, held other views which he developed subsequently in the lecture to which I 

 have referred. 



But I think it only just to point out that, however much the views of Mr. Ball 

 and of M. de Candolle may differ in detail as to the way in which the results were 

 brought about, there is a substantial basis of agreement in the recognition of the fact 

 that there is an element of great antiquity in the Alpine flora which cannot be simply 

 accounted for on the hypothesis of a migration from the north during the glacial epoch. 

 As de Candolle shows, some of the most ancient fragments of the Alpine flora are now 

 to be found only on the souUwim slopes of the Alps. This is the case with species of 

 Primula, Pedicularis^ and Oxytropis^ which exist neither in the interior of Switzerland 

 nor in the North of Europe. De Candolle further points out that the Alpine species of 

 Camjjamila peculiar to Mont Cenis, the Simplon, and the neighbouring valleys, are not 

 related to Arctic species, but to those of mountain-chains to the eastward. 



Both these distinguished botanists were agreed in admitting that the glacial period 

 must have played an important part in modifying the Alpine flora. Mr. Ball, however, 

 was somewhat disposed to minimize its effect. To him the Alpine flora was a fact of 

 great antiquity which the glacial period practically left unmodified. He continues: — 



" I could name a few plants whose present habitat on the mountains of Central 

 Europe may probably date only from the glacial period, and there are a few others that 

 have perhaps come in recent times from the mountains of Northern Asia ; but I venture 

 to affirm that the effects of the glacial period both on the distribution of plants and on 

 the climate of Europe have been greatly overrated. Even during the period of maximum 

 cold the highest ridges of the Alps were not completely covered with snow and ice ; for 

 we still see by the appearance of the surface the limit above which the ancient ice did 

 not reach, and in the middle zone the slopes that rose above the ancient glaciers had a 

 summer climate not very different from that which now prevails. In my opinion the 

 effect of the glacial period on the growth of plants in the Alps was to lower the vertical 

 height of the zones of vegetation by from one to two thousand feet." (Proc. B. Geogr. 

 Soc. 1879, p. 584.) 



De Candolle, on the other hand, thinks that a large element was driven south, and 

 subsequently regained its footing only on the southern face. 



Apart from the fact that the Table forms a minute and probably very accurate piece 

 of botanical topography, it must, I think, be evident from these considerations that a 

 detailed study of the distribution of plants on the southern slopes of the Alps was not 



* 1 may refer, for those who have difficulty in consulting the original paper, to a brief abstract which 1 com- 

 municated to ' Nature' for April 27, 1876. 



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