FLO*RA OF SCOTTISH LAKES 
161 
geography to be discovered, on the basis of physiological anatomy 
and plant-psychology. By such methods a most interesting inquiry 
would be — What is the equilibrium that has been attained between 
the forces of resistance and traction that has caused certain species to 
arrive at, and remain in, restricted areas ? 
The two great factors that contribute towards the distribution 
of the plant-covering over the surface of the earth, and through its 
waters, are food and climate. Notwithstanding the conditions for 
plant life being so often remote from the ideal, yet the plastic power 
that plants possess of adapting themselves to the various combina- 
tions of edaphic and climatic conditions is so great that there are 
comparatively few spots in which some plant or other is not able to 
thrive and carry on its metabolic activities. With aquatic plants the 
influence of the substances, food or otherwise, held in solution in the 
water, is vastly greater than that of climate. 
The edaphic conditions dominating the flora in the majority of 
highland peaty lochs are indirectly influences of climate. Indeed, the 
rock-basins that contain the lakes are themselves chiefly the result of 
climatic effects, because they were scooped out during a former period 
of glaciation. This is also to a great extent true of the lowland 
lochs, such, for example, as those of Fife. The study of the lake 
flora leads, therefore, to the consideration of the cause of a glacial 
epoch, and is thus the usher to a most abstruse problem. 
The yellow-brown colour of the waters of the Highland districts 
is a matter of common observation, and is due to the water-supply 
from the mountains percolating through enormous quantities of peat 
before reaching the lakes. This, then, would appear to be an edaphic 
influence, and so it is, but the existing conditions — the presence of 
peat on the mountains — have been brought about by direct climatic 
influence. The climatic conditions that obtain in the exposed 
portions of the Highlands are more favourable to the natural produc- 
tions of moorland than of either forest or grass-land. These three 
formations of dominant types of vegetation — moor, forest, and grass 
— are antagonistic to one another, the tendency being for the moor- 
land vegetation to extend from the higher situations over the natural 
forest and grass-land of the lower altitudes, to their extinction. The 
principal natural causes for the victory of moor over forest and grass 
are: — (I) wind, which is much less antagonistic to moor plants 
than to trees, because the former are much nearer the earth, and 
therefore feel the destructive desiccating action of wind very much 
less than trees do ; besides which the dominant moor plants have 
protective adaptations against wind which trees seldom possess ; (2) 
the peculiar acid humus that is formed so abundantly, in the form of 
peat, from the remains of certain dominant moor plants, and which 
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