SURVIVALS. 
103 
Similarly are there plenty of survivals amongst plants. The 
ferns of the epoch when coal was a flourishing vegetation, are 
wonderfully like the ferns of to-day. The horsetails of the 
genus Equisetum have no modern allies, but constitute a family 
as well as a single genus. We know, however, that many mem- 
bers of the Equisetacese abounded in the coal period. The 
screwpine of tropical swamps stands alone now, but we find 
plenty of remains in the London clay at Sheppey. So, too, the 
Casuarina or Beefwood of Australia and the Nutmeg represent 
other nronotypic families, and are survivals. 
To come down again to the Pleistocene or the Great Ice Age. 
There is an existing so-called Arctic flora, because it is scattered 
over the Arctic regions, the members of which are wanting in 
the temperate plains of England and the Continent, but several 
of them reappear on the mountains of Scotland, Wales, 
Pyrenees and Alps. How did they get there ? 
It is the belief of geologists that after England had been sub- 
merged, with the exception of the mountain tops, which fur- 
nished glaciers and icebergs, the island rose out of the sea, 
perhaps 1,000 feet or more higher than at present, thereby con- 
verting the German Ocean into a plain, across which the Arctic 
flora spread, as the climate of these areas was at that time 
arctic in character. Thus we find, for example, remains of two 
species of creeping willows, Salix lierbacea and Salix polaris,* truly 
Arctic species of willow, at Bovey Tracey, in Devonshire. But 
as the climate became more and more temperate, other plants 
adapted to this new condition invaded the lowlands, and so 
those of the Arctic flora which could survive the somewhat less 
Arctic features of our European mountains had to content them- 
selves with the higher altitudes of the mountain regions, and 
there they remain to this day. Others, like Salix polaris, died 
out, as it is now only found in Arctic regions. 
If, therefore, it be true that the environment is the moving 
cause of change, as long as that is such as the plant is adapted 
to there is no a priori reason why it should change at all, but 
exactly the reverse. Indeed, Salix polaris and its congener S. 
lierbacea are rather instructive plants. For while the former is 
now confined to high latitudes — specimens in the Kew Her- 
barium were received from Iceland, Greenland, Spitzbergen, 
Nova Zembla, Behring’s Straits, Siberia and Lapland — and as 
far as they show there is little or no variation of importance ; 
* With regard to S. polaris , it is doubtful if it has ever been cultivated ; for 
though it is said to have been grown in the willow garden at Woburn Abbey, 
and the late Mr. Borrer gave me a specimen from his own garden at Henfield in 
Sussex ; neither were true S. polaris. This latter appears to be the same as the 
former, and perhaps was derived from the specimen at Woburn, which is figured 
on pi. 63 in the “ Salicetum Woburnense.” This, however, certainly does not 
represent S. polaris ; but in the opinion of Dr. F. Buchanan White, our greatest 
living authority, is probably a hybrid between S. lierbacea and S. arbuscula , 
which he calls S. simnlatrix. 
