The Origin of our British Flora 
Caucasus. In Eastern North America, Greenland and 
Europe, the trees were also closely allied to one another. 
The Alps possessed already such modern flowers as 
Campanulas, Saxifrages, Primulas, Veronicas, Androsace, 
and Rhododendrons, and though, as is the case to-day, 
each mountain group had a flora of its own, yet certain 
species wandered from mountain to mountain keeping 
to the higher summits.? 
Even to-day in Japan and East Asia one may discover 
in the high alpine regions a few Scotch mountain plants 
such as Phleum alpinum, Oxyria, Sibbaldia, and the 
common butterwort? 
There are instances which show how after the great 
ice invasion the same species has been separated and 
confined in two distinct and distant mountain systems. 
Thus Erigeron frigidus grows in the Sierra Nevada of 
Spain and also in South-west Persia ; Scutellaria orientalis 
is found only in Spain and in Asia Minor ; Saponaria 
glutinosa in Spain and in the Caucasus. This shows the 
ruthless division of kindred by the projecting fingers of 
the northern ice.* 
But just as interesting are those cases in which a 
number of little special forms of one genus belong to 
the various mountain ranges. 
Cardamine shows this very beautifully, for there are 
forms from the Pyrenees (1 sp.), Alps (4 sp.), Apennines 
(3 sp.), Caucasus (6 sp.), Himalayas (7 sp.), and North 
America. Besides these our own cuckoo-flower ranges 
all round the North Pole and through the Arctic regions, 
whilst C. impatiens may be found anywhere from Scot- 
land to the Pyrenees, and all the way to Japan. 
Many of these northern alpine and subalpine species 
have even invaded the highest summits of tropical 
Africa, such as Ruwenzori, and even Kenia and Kiliman- 
jaro, whilst others have outliers which occur in the 
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