Cll PROCEEDINGS—PERTHSHIRE SOCIETY OF NATURAL SCIENCE. 
any inability to resist the greater heat of the valleys, for experiment 
will show that in many cases, at least, that is not detrimental to them, 
but because in the valleys they are choked by the greater vigour of 
the lowland plants. That the commoner constituents of our mountain 
flora overran at one time the whole country is shown by their 
present distribution and occurrence in localities separated from each 
other by lowland areas. But although we have thus tolerably con¬ 
clusive proof that the alpine flora, as a whole, was at first a lowland 
flora, which was in course of time to be driven up the hills, when we 
come to consider the present distribution of some of the component 
species, we are met by problems which are not easy of solution. 
Putting aside the species which are now, at least, if they were not 
always, local or rare in this country, there are some common species 
whose distribution is difficult to explain. Why, for example, should 
several very common alpines (e.g., Alchemilla alpina and Saxifraga 
aizoides) occur in north England, in a great part of Scotland, and in 
Ireland, and yet be absent from the Welsh mountains? On the 
other hand, why should another common alpine, Epilobium anagallidi- 
folium , be found in north England and Scotland, and not in Wales nor 
Ireland; or E . alsinefolium in Wales, north of England, and Scotland, 
and not in Ireland ? Possibly the explanation is that those which 
are absent from Wales, but are present in Ireland, reached the present 
British coast north-east of the latitude of Wales, and found a road 
open for them northwards but not southwards, and got to Ireland by 
way of Scotland. The origin and distribution of the western and 
south-western plants afford other problems. Mr. Barclay has cited 
various theories regarding the species of heath which are confined 
(in these islands) to Ireland and the extreme south-west of England. 
As, however, there was direct land communication with the north of 
Spain, the origin of these do not present such difficulties as there 
are, for example, in the case of Eriocaulon septangulare. 
Before proceeding to the proper subject of this address, there is 
one other matter which may be briefly noticed. From the many 
constituents which our alpine flora has in common with the Nor¬ 
wegian one,—there being very few instances of a Scottish alpine plant 
not being also Scandinavian,—it is not uncommonly supposed that 
our mountain plants immigrated from the north. In a sense, no 
doubt, this is correct, but not if a direct immigration is meant. All 
the northern plants were driven south by the increasing ice sheet, 
and hence the flora of the plains of the southern part of Mid Europe 
was, at the period of the climax of the ice age, a mingled northern 
and alpine one. When these plants began to follow the retreating 
ice, some of the alpine species reached Britain, but did not get north 
to Scandinavia; and some of the northern plants came to Britain, 
but did not go to the alpine regions of Mid and South Europe. In 
this way we have in Britain alpine plants which are not arctic, and 
arctic plants which are not alpine; but all our hill plants, whether 
their original habitats were in the north or in the x\lps, came, like the 
lowland flora, from the plains of Mid and South-Mid Europe. 
The species, both lowland and alpine, which came into Britain at 
this period of land extension constitute the bulk of what may be 
