Illl-: r.lM'llSll AND SWl.sS ALIMNK FLoKAS. 
51 
mountain groups. In Lho central Alps of the Bernese Oberlaiid the 
downward limit of the alpine and sub-alpine zones is considerably lower 
than in the southern alps of the Yallais. 
Let us now consider whether it is possible to distinguish an alpine and 
sub-alpine flora in the mountain regions of Britain. 
IhiiTisH Alpink and Suh-Ali'1ne Zones. 
From a comparison of the British and Swiss floras as a whole, we 
have seen that a very close relationship exists between them. The 
Swiss flora is not relatively greater in number of species than we should 
be led to expect when we take into account its more southern situation. 
For, as is well known, vegetation generally tends to increase as we leave 
the Poles and approach the Equator. 
The latitude of a central point in the Swiss Alps, such as the Jungfrau, 
is about 46^° N., while that of Ben Nevis is roughly 56^° N., a difference 
of ten degrees. Taking into account this difference in latitude, we should 
naturally expect to find an alpine flora in Britain at a considerably 
lower elevation than in the Alps. The height of Ben Nevis, our highest 
mountain, is about 4,400 feet, while the average height of our loftier hills 
is between 2,000 and 3,000 feet. Other things being equal, a difference 
of ten degrees in latitude wwld probably bring the summits of many of 
our British mountains well within the alpine zone, although they w^ould 
be entirely sub-alpine if in the latitudes of the Alps. It must, however, 
be remembered that latitude is not the only factor which must be taken 
into account. The climate of Britain is in many respects anomalous ; 
for, owing to our insular situation and the proximity of the Gulf Stream, 
our mean average temperature is considerably above that of many places 
in the same latitude but less favourably situated. While, therefore, we 
may conclude that the British alpine zone will be found to extend to 
considerably lower elevations than in the Alps, the effect of climate is 
too complicated to allow of any exact approximation as to the limits of 
that zone from a comparison with that of Switzerland. For this we 
must rely chiefly on observations as to the distribution of our mountain 
plants in such a region as the Scotch Highlands. 
If we examine the phanerogamic flora of our highest mountains, we 
at once arrive at the conclusion that an alpine flora undoubtedly exists 
in Britain. It is true that the flora is small, and often extremely local 
in its distribution. The fact remains, however, that in Britain we find a 
considerable number of species which are for the most part confined to 
high elevations in our mountain groups. We have therefore the begin- 
nings of an alpine flora in Britain, which, if our mountains had only 
been a little higher and more compact, would possibly have rivalled that 
w'hich is to-day one of the chief glories of the Alps. The close consan- 
guinity which exists between the British and Swiss floras as aw^hole, and 
which, as we shall shortly see, extends to their alpine sections, renders 
this almost certain. 
A detailed examination of the flora of our mountains shows that w^e 
can divide it into four classes : — 
1. Plants which are only found at high elevations, and do not descend 
below 2,400 to 2,500 feet. 
E 2 
