SKETCH OF THE FLORA OF THE PROVINCES 4] 
the more maritime climate. This last factor is greatly 
neutralised by the absence of shelter. The contrast 
between the flora of the Outer Hebrides and most of the 
islands in the Inner group, due to their different geological 
formation, and to the configuration of the land, does not 
apply to Hepatic, although readily observed in the case 
of phanerogams. The larger amount of sheltered ground 
in the Inner islands, the presence in some of them of lime- 
stone, the extreme barrenness of all the higher hills which 
have been examined, account for what difference there has 
been observed between the two groups. The stony summits 
of the Paps of Jura and Ben More in Mull are only equalled 
by the bare rocks of the Gabbro of the Cuchullin Hills in 
Skye, and doubtless also those of Rum. 
The absence of shelter in the Hebrides has the usual 
result in scarcity of trees. Woods and copses are very 
local in the Inner group and almost absent in the Outer 
islands. Most of the species which occur in such situations 
on the west coast mainland have been found in the Inner 
Hebrides, but, as is to be expected, much more locally. 
Such species are also frequently found in sheltered ground 
among sea-cliffs, and in this way are also found to occur in 
the Outer islands. Atlantic species which require shelter, 
such as the small Lejewnew, are local; but where deep 
ravines or greatly sheltered rocks are present, as in parts 
of Mull, they are found plentifully. The more maritime 
climate of the islands portrays itself by the abundance of 
the few Atlantic species which do not require much shelter 
when on the west coast, such as Saccogyna viticulosa and 
Frullania germana. All the larger islands contain peat- 
mosses in more or less abundance, but in some of the 
smaller islands, as Tiree, what peat there was at one time 
has practically all been used as fuel, and in this way Tiree 
differs greatly from such an island as the neighbouring 
one of Coll. 
NortH HIGHLANDS 
As this district comprises the whole of the northern part 
of the mainland, we have both an eastern and western 
flora. The province has not been so widely examined as 
the others have, and this especially applies to the upper 
