Flora of Scottish Lakes. 
101 
1909-10.] 
At a few feet above the normal water level quantities of lichens clothe 
the rocks and give the littoral a distinctive character. The most abundant 
of these lichens are Lecidea geographica, Parmelia omphalodes, and 
Sphserophoron coralloides. The first mentioned is so plentiful, and so com- 
pletely does it overgrow the rocks, that many parts of the shore are for 
considerable distances coloured bright yellow, and the zone to which its 
abundance is restricted presents a remarkable appearance. This rocky 
zone is in reality at the ancient water level of the loch previous to a reduc- 
tion of its level by about 7 feet some 150 years ago. This lowering of 
the level was brought about by the construction of a tunnel for the effluent 
instead of the natural outflow, for the double purpose of reclaiming land at 
the margin and admitting salmon to the loch. Why the Lecidea should be 
so abundant at the old water level I am unable to explain. 
I dredged this loch in a great many places from end to end, but beyond 
an average depth of about 7 feet no living plants could be obtained from 
the bottom. Yet in suitable places the bottom from 2 to 7 feet deep 
often bears an abundant vegetation, which occasionally may be continued 
into the shallower water : Littorella lacustris, for example, is plentiful in a 
few sheltered sandy creeks. The extinction of the submersed Phanerogams 
at so shallow a depth as 7 feet is distinctly remarkable because it is 
not brought about, as in some cases (ante, p. 1015), by the discoloration of 
the water. Here the bottom can be seen at a depth of 7 feet when 
looking over the side of a boat, without the use of any apparatus beyond 
shading the eyes with one’s hat in order to shut out the light reflected from 
the surface of the water. Reasoning, therefore, from similar cases of 
translucency, some vegetation should extend to a depth of 28 feet or more.* 
It has already been indicated (p. 66) that the grass-like associations of 
plants which cover the moors and mountains have an influence upon the 
flora of the lochs in this Area. At the first consideration one would 
imagine that the influence exercised upon the bottom flora of a loch by the 
substitution of grass-like plants over the moors, instead of associations of 
Ericacese, would be that of less peat- extract getting into the water. Such, 
however, is scarcely the case, because the moors have an abundance of 
ancient peat below the grass, formed there previous to the development of 
the sheep-rearing industry. The influence is caused in a way one would 
little expect. In winter the dead leaves of the grass-like plants covering 
the moors, chiefly Molinia cserulea, which grows very luxuriantly here, but 
also Nardus stricta, Scirpus csespitosus, etc., are blown or washed into the 
burns and drains, and are thence carried into the lochs. There, owing to 
* The Geographical Journal , January 1908, p. 68. 
