CONDITIONS AFFECTING DISTRIBUTION. 61 
number of these groups; but in certain places they present 
themselves in a number of species and of individual plants 
giving to the vegetation of the place its particular 
character. 
‘When on a map there are marked the districts in 
which the different groups of plants principally predo- 
Minate we discover that with the one exception of the 
most common species the development of groups is not 
continuous. The Arctic flora only shows itself it its 
characteristic form, here and there, in scattered colonies, 
separated by extensive species in which the Sub-Arctic 
predominates. The boreal flora also presents itself 
scattered over the low-lying districts of the eastern portion 
of the country around the Christiania fiord, and the Miosen 
lake, then at a distance to the west, beyond the Lang- 
fjelde, near the inland branches of the fiords of the 
western littoral, and lastly on the low lying lands on the 
north of the country. On the intermediate low lying coasts 
the Atlantic flora reigns. This is equally with the others 
isolated by the greater part of the Atlantic species find- 
ing themselves in the south-west portion of Sweden, but 
not around the Christiania Fiord. Some which have only 
been fuund on the west coast of Norway, find theinselves 
again only on the west and the south coast of the German 
Ocean.’ 
Dr Broch goes on to say:—‘The present flora of 
Norway cannot have always existed there. At a 
geological period, which is not very distant, the pen- 
insula, up to the most remote plateaux of the land, was 
covered with a bed of ice and snow, overlooked only by 
the bare summits of some few of the most elevated moun- 
tains. At this time the trees, shrubs, and plants, which 
now beautify the valleys could not have lived. They 
existed, however, anterior to the so-called glacial period 
on other parts of the terrestrial globe. They have been 
found in a fossil state in beds of coal deposited prior to 
this period. It is an immigration from other countries 
