1909-10.] Flora of Scottish Lakes. 101 



At a feAv 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 

 Sphaerophoron coralloides. The first mentioned is so plentiful, and so com- 

 pletely does it overgrow the rocks, tliat 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. QQ) 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 

 Ericaceae', would be that of less peat- extract getting into the water. Such, 

 however, is scarcely the case, because the moors liave 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 tlie dead leaves of the grass-like plants covering 

 the moors, chiefly Molinia cserulea, which grows very luxuriantly here, but 

 also Nardus stricta, Scirpus caespitosus, 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. 



