The Origin of our British Flora 
and S. arbuscula), of the dwarf birch, Arctostaphylos, 
Empetrum, and the blaeberries (Vaccinium myrtillus 
and V. uliginosa),* and may have resembled the usual 
arctic tundra (see p. 92). But there are several sub- 
arctic plants which ought to be added to this list, but 
which would not occur in those peat bogs from which 
evidence on these questions is usually obtained. Thus 
scurvy grass, Armeria, and Plantago maritima are both 
arctic plants, seashore plants, and also occur as alpines 
or sub-alpines in Scotland. It has sometimes been found 
difficult to understand why they should grow both along 
the sea and on rocky ledges at over 2000 feet. But 
the occupation of the land began on the seashore and 
gradually extended to the hills, so that the mountain 
scurvy grasses probably flourished at some time or other 
in all the intervening regions where they have been now 
choked out by other species. 
Besides these, several estuarine and marsh plants, 
including some of the most important land-formers, can 
also endure an arctic climate. There are, ¢.g., Scirpus 
Tabernemontani and S. lacustris, Phragmites, the two 
Triglochins, Menyanthes, Litorella, and others which 
seem to range into the subarctic, if not always to the 
true arctic regions. 
So that even in the Dryas time there may have been 
quite a considerable occupation and ‘colonisation of the 
river valleys and estuarine mud, 
For the next or birch time, perhaps the North Cape 
of Norway or the Lofoden Islands might be the best 
example. It was still a very cold Britain with a July 
temperature of only 9° C., and in August 7° to 8° C. 
Along with the birch were alder, hazel, and probably 
dwarf juniper. On the Continent Populus tremulus, the 
aspen poplar, seems to have been characteristic. With 
* Lewis, 
222 
