376 Relation of the Plant Population to the Glacial Period. 
possible to believe that the plants of the south of England, 
many of which can barely hold their own during a severe 
winter nowadays, could have survived these arctic conditions ? 
If the southern plants were completely swept away by the 
cold, the question arises: How did they come back again, 
especially to islands like Ireland and the Isles of Scilly, and 
how did they obtain their very singular present geographical 
distribution ? We are told that the matter is simple enough, 
for Britain has often been connected with the Continent, and 
the plants spread slowly overland. However, before we adopt 
the view that for animals and plants to spread to islands it is 
needful to have land-connection, you should remember Kraka- 
toa, and the rapidity with which the exterminated flora has 
come back. Also I must point out that there are peculiarities 
in the distribution of the different elements that go to make 
up the existing British flora that no land-connection will explain. 
Look at the recent distribution. One of the most striking 
peculiarities is the Pyrenean element in our flora. It is practi- 
cally confined to two areas, the one in Cornwall and the other 
in the West of Ireland. Geologists nowadays will not agree 
to the reconstruction of a lost Atlantis to account for this 
peculiar distribution. 
Undoubtedly since the Glacial period our islands have seen 
several oscillations of level. There has also been widening 
and narrowing of straits and channels. England has been 
connected with France near Dover, and also across the North 
Sea with Holland and Denmark. But 20 or 25 metres seems 
to have been the approximate extent of the rise in the south 
of England. I have searched in vain for evidence of a greater 
movement. A shallowing of the sea by 25 metres is not 
nearly sufficient to connect Ireland with England or Scotland, 
or the Isles of Scilly with England. Still less would it suffice 
to connect the West of Ireland or Cornwall with the Pyrenees, 
where the peculiar plants find their home. A rise of land to 
this amount would not even bring Scilly and the Land’s End 
appreciably nearer together. 
This limitation of the extent to which we can bridge over 
the gaps between our islands is, however, a point on which 
there is much difference of opinion, and I will not insist on the 
conclusiveness of the evidence as to the extent of the oscilla- 
tions. 
. From the botanist’s point of view there are, however, other 
archipelagos besides those surrounded by water. No doubt 
if we can postulate sufficient orographic changes plants would 
spread slowly from land to land during the few thousand 
years that have elapsed since the cold died away. But—and 
this ‘ but ’ is all-important—they would only do so if the soils 
were suitable. An isolated tract of limestone surrounded by 
Naturalist, 
