Till-: r.IMTISH AND SWISS ALIMNI-: I'T.oKAS. 59 
the world. He concluded that this flora was orii,nnally developed in 
Scandinavia, and that it flourished there before the Glacial peiiod. 
During that period it was driven southward by the approaching ice, and 
afterwards, when the cold became less intense, part of it remained in the 
Alps, while the i-cst spread over Europe or returned to the Arctic regions. 
The late Mr. John l^all,* in a paper on the origin of the flora of the 
European Alps, criticised Hooktr's theory by doubting whether the 
present Arctic flora existed before the Glacial period in those regions. 
On the other hand he suggested that a certain portion of the alpine flora 
may have been carried there by the retreating ice, and that the European 
alpine flora probably gave rise to the present Arctic flora, and not vice 
versa. Ball found that nearly half of the plants stated by Hooker to 
extend beyond the Arctic Circle are ubiquitous, owing to their power of 
adaptability, and that there was no reason to suppose that they originated 
in those regions, especially as they flourish to-day most abundantly in 
the temperate zone. 
The foundation of Hooker's theory must, therefore, be regarded as 
open to severe criticism. It is, however, the best explanation of the 
origin of the alpine flora which has, so far, been put forward, and it has 
been adopted by many botanists. It is also of special importance in 
laying stress on the fact that any explanation of the origin of the Alpine 
flora must also account for the origin of the Arctic flora. 
To return to the consideration of the Swiss alpine flora as it exists 
to-day. The distribution of alpine species in Switzerland is, as has 
already been mentioned, very uneven. The Swiss Alps may be divided 
into three very natural districts : the Central Alps or Bernese Oberland^ 
the Southern Alps of the Vallais, and the Eastern Alps of the Grisons. 
Of these the Central Alps are much the poorest in number of alpine 
species, and those of the Vallais much the richest. Many attempts have 
been made to account for this inequality of distribution, notably that of 
de Candolle aiready mentioned. The question is one which is, no doubt^ 
bound up with that of the origin of the alpine flora in general, and until this 
greater problem has been solved we can hardly hope for a satisfactory 
explanation of these inequalities in distribution. 
In considering the distribution of species over any area it is necessary 
to take into consideration another factor which we have not, so far, 
touched upon — namely, the character of the soil. The influence of the 
soil on vegetation, especially in regard to the distribution of alpine 
species, is rather puzzling. In Switzerland the rocks are mainly lime- 
stones and crystalline igneous rocks such as granites, gneisses, and schists. 
Certain species of alpines are apparently confined to one or other of these 
formations, while others seem to be indifferent as to the nature of the 
soil on which tbey grow. The two species of Rhododendron, which we 
have seen to be especially characteristic of the alpine zone, are cases in 
point. B.ferrugineuin, L,, is indifferent as to soil, while B. hirsiitum, L., 
is confined to limestone regions, and does not occur where igneous rocks 
predominate. Another instance is that of Anemone alpina, L., and its 
variety sulphurea, L., the latter only occurring on granite soil. If, how- 
ever, we trace the distribution of alpine species over a much larger area 
* Ball, J., Royal Gcogra2)hical Society's Proceedings, 1879, vol. i. p. 564, 
