FLORA OF SCOTTISH LAKES 
165 
example, on the other hand, that plants can develop, and luxuriantly 
too, on a rocky shore subjected to powerful erosion ; but the case is 
here entirely different. The seeds of phanerogams, excepting the 
tropical Podostemaceas, have no power to firmly attach themselves to 
rocks and stones, as have the spores of seaweeds. Still we do find, 
even in exposed parts of the lakes, fixed rocks often covered with 
mosses, hepatics. Algae, etc. Wind is also an important factor in 
dwarfing the semi-aquatic vegetation about the littoral region of the 
lakes ; especially is this the case with those that are situated in the 
more elevated and exposed positions. 
The sudden rise or fall of water to any great or prolonged extent 
is inimical to the well-being of plants in the lochs, particularly so if 
the water is extremely peaty. This is very pronounced at Loch Mhor, 
where an ever-changing level — due to the rainfall on the one hand, 
and the water used by the British Aluminium Company at Foyers on 
the other hand — does not allow a flora to grow at all. 
The great variation between the summer and winter temperatures 
of the water of the higher mountain lochs doubtless affects the flora 
to a greater extent than in those of lower altitude. These hill lochs 
are often shallow, and the comparatively small body of water may 
become heated to 70° Fahr. in summer, and may frequently be covered 
with ice in winter and spring, the ice often remaining upon such 
lochs until April. Before its final disappearance, large shoals of 
broken ice grind upon the shores with surprising power and noise, 
and would destroy any littoral vegetation within its influence. Con- 
sidering that such floating ice shifts about the loch with every change 
of wind, it is scant wonder these hill lochs are so often found devoid of 
marginal vegetation. In the great body of water of the large and 
deep lochs of lower altitude, the temperature is more equable, winter 
and summer records not varying more than 10" to 20° Fahr., and 
such lochs seldom freeze. 
In the peaty lochs the aquatic plants are usually remarkably free 
of epiphytic organisms and also of mud. Humic acids, and perhaps 
carbonic acid too, in the waters almost extinguish molluscan life. 
Consequently, one does not find the aquatic vegetation destroyed by 
these creatures as is commonly the case where certain of them, especially 
Limnaese, abound. There being little or no calcium bicarbonate in 
peaty waters, there is consequently no incrustation of calcium carbonate 
upon the aquatic plants. A necessary corollary to such antecedents is 
that no lime deposit resulting from the metabolism of plants is being 
laid down in these peaty lochs, as is the case where the water is charged 
with calcium bicarbonate. In the lochs at Lismore, for instance, the 
mud at the bottom is gray in colour, and feels gritty to the touch, 
which is due to the lime from the plants. 
