SVS. 
THE RELATION OF THE PRESENT PLANT POPULA- 
TION OF THE BRITISH ISLES TO THE GLACIAL 
PERIOD.* 
CLEMENT REID, F.R5S., F.L-S., F.G.S. 
Tue distribution of our British plants has long been a puzzle 
to the botanist, and no explanation was forthcoming till the 
cause was searched for in bygone changes of climate, and 
changes in the distribution of land and sea. A century ago 
it was generally supposed that species had originated mainly 
in the districts in which they were then found. But even 
under this hypothesis the anomalies of discontinuous areas 
seemed to require explanation, for the same species was not 
likely to originate at several different points. 
With the growth of the idea of gradual evolution it was 
realised that faunas and floras had a past history, even if the 
included species had remained unchanged. Botanists recog- 
nised that there were many points that required explanation. 
For instance, it was noticed at an early date that each of our 
mountain-tops possessed a small outlying fragment of the arctic 
flora. How came it that the same species occupied so many 
different mountains? This seemed a perfectly fair subject 
of inquiry, even to naturalists who hated the very idea of 
evolution when applied to species and genera. 
More than sixty years ago a great impetus was given to 
this study by the discovery that Europe had passed through a 
most remarkable series of climat c changes, and that, too, 
during the lifetime of the existing species of animals and plants. 
There had not been a mere cooling of the climate; the tem- 
perature in these latitudes had sunk far below its present level, 
and then had again risen. 
Edward Forbes, in 1846, seized this clue, and explained 
through it, as relics of the Glacial Period, the arctic plants 
stranded on our mountain-tops ; they were plants left behind 
when the climate became too warm for them any longer to 
survive on the plains. The subsequent discovery of fossil 
remains of these plants scattered over the plains, and often 
associated with relics of arctic animals now extinct in Britain, 
seemed a brilliant proof of Forbes’ view, which has been 
generally adopted. 
In some curious way, however, botanists and zoologists 
both seem to have overlooked the difficulty that, granting 
Forbes’ hypothesis to be sufficient to account for our alpine 
flora, it rendered more difficult instead of easier the explanation 
* Read to open the discussion at a joint meeting of the Geological 
and Botanical Sections at the Portsmouth meeting of the British Asso- 
ciation. 
agit Nov. I. 
