52 
JOURNAL OF THE ROYAL HORTICrLTURAL SOCIETY. 
2. Plants which flourish most kixuriautly above 2,400 feet, but which 
occasionally descend to low elevations, or sometimes even to the sea- 
level. 
8. Plants which are rare or absent in the lowlands, and which are 
not known to ascend above 2, TOO to 2,500 feet. 
4. Plants which are typically lowland, and as a rule widely distributed 
over the plains of Britain, but which ascend to considerable elevations in 
the mountains. 
The plants included in Class 1 and Class 2 we may term alpines, and 
we may roughly estimate the lower limit of the alpine zone at about 
2,400 to 2,500 ft. in the typical area of the Scotch Highlands. In the 
Lake District and in the Welsh mountains the limit is probably some- 
what higher. The species in Class 2 are in the main restricted to 
elevations above 2,500 ft. 
A knowledge of the elevation at which a species occurs elsewhere, 
especially in the Swiss Highlands, is often useful in determining whether 
a plant found at a slight elevation in Britain is alpine or sub-alpine. 
It must, however, be remembered that this rule is not always to be relied 
upon, since many species which are restricted to the alpine or sub- alpine 
zones in Switzerland are commonly met with as typical lowland plants 
in Britain and Northern Em-ope generally. 
The range in altitude in Britain is very limited, even hi our highest 
mountain groups, as compared with the elevations to which plants ascend 
in the Alps. Even in Switzerland we have seen that the lowland, 
sub-alpine, and alpine zones pass imperceptibly from one to the other. 
This is still more marked in Britain, the range of elevation being so 
short. On this account we can hardly distinguish a sub-alpine zone at 
all in Britain. We may, however, designate those species which have 
the distribution indicated in Class 3 as sub-alpine, but it is not possible 
to fix even rough limits for this zone. Our mountain flora is also too 
limited for the occurrence of characteristic alpine and sub-alpine species — 
which we saw to be so useful in the Alps to distinguish between the 
various zones — to be of any service in Ih'itain. 
The British Alpine Flora. 
The British alpine flora is, as has been already stated, comparatively 
small, and often extremely restricted and local. Thus certain species, 
such as Erigeron alpinum, L., Gentiaiia nivalis, L., and some others are 
conflned to the l>readalbane and Clova ^Mountains in Scotland. Arahis 
alpina is conflned to the Island of Skye. Others, again, are still more 
local, Saxifraga cernua, L., is only found on the summit of l>en Lawers, 
B.nd Llojjdia serotina, Reich., on the Snowdon range. Several species have 
become extinct in recent times. On the other hand, such species as 
ThalictriLin alpinum, L., Silene acaulis, 'L.,Dryas octapatala, Ij., Cerastium 
alpiimm, L., are comparatively common on many of the mountains of 
Scotland, England, and North Wales. Several alpines are known in 
certain places to descend to the sea level, among others TJuiIictrum 
alpbmm^ L., Draha incava, L., Saxifraga oppositifolia, L. 
