14 THE DISTRIBUTION OF HEPATIC IN SCOTLAND 
ATLANTIC SPECIES 
THE Atlantic species of hepatics are those which are 
confined, or almost so, to the west coast of Europe, includ- 
ing a short distance inland and the Atlantic islands, a few 
extending along the Mediterranean, and still fewer being 
also found in subtropical and tropical America, the West 
Indies, and other parts of the world. These species are 
more plentiful in the British Isles than in other parts of 
Europe, some being only known from our island. 
The first fact to be noted is that the prevalence of the 
Atlantic species in Scotland is, in general, proportionate to 
their proximity to the west coast; the further one goes 
eastward, the rarer they become. The actual proximity of 
the sea on the east coast does not favour their occurrence 
except in a very few cases to be afterwards mentioned. 
The distribution of Hepaticw is mainly dependent on 
climate, the chief requisite being moisture. In the case of 
nearly all Atlantic species an absence of a low extreme of 
temperature is also necessary. This combination does not 
extend far from the west coast, and the distance to which 
it extends marks the point to which these species are 
prevalent. Next to moisture in the atmosphere the most 
important requisite is the physical condition of the soil. 
Where the nature of the rocks is such that their disintegra- 
tion does not form a moist and retentive soil, it will be 
found that even under the otherwise most favourable 
conditions on the west coast Atlantic species are scarce or 
absent. This is very noticeable in ravines running through 
sandstone and some volcanic rocks. Nearly all species of 
hepatics are scarcer in such ravines, but the Atlantic species 
being the most delicate, are affected in a more marked 
manner. 
The next point in treating of the distribution of these 
species is that too much importance must not be given to 
the watershed dividing Scotland west and east. Water- 
sheds in themselves have no relation to the distribution 
of Heputicw, whatever they may have in the case of 
phanerogams. ‘The north and east sides of the watershed, 
with their constantly moist ground, have hepatics in plenty, 
