FLORA OF SCOTTISH LAKES 
213 
In contradistinction to the lakes of the Ness Area, the water of 
the Lismore lakes is pellucid. It is so clear that one may look over 
the side of a boat and see the bottom through 25 feet of water. 
In consequence of their clearness, the photic zone for the more 
highly organised plants is less restricted than in the Ness Area. The 
shores also present quite a different aspect from those of the peaty 
lochs. Here the rocks and stones are covered with an incrustation of 
lime, which gives them a peculiar sponge-like appearance. The 
rounded, water- worn, and polished stones found on the shores of Loch 
Ness are not to be seen at Lismore. As the lakes are sheltered from 
the wind by low hills, their shores are not subjected to frequent and 
powerful erosion by the waves ; they are consequently more or less 
surrounded with a littoral vegetation. Many of the plants in these 
lochs are heavily coated with an incrustation of carbonate of lime, a 
phenomenon unknown in the Ness Area. Myriophyllum spicatum, 
for example, is so burdened in this way that the plants are mostly 
unable to rise to the surface for the purpose of pollination ; as the 
plants remain submerged, fertile specimens of this species are con- 
sequently not common in these lochs. Calcium carbonate (CaC03) is 
but slightly soluble in pure water ; the presence of carbonic acid, 
however, enables the water to take up considerable quantities in the 
form of bicarbonate [Ca(HC03).,], and hard water results from its 
occurrence in this soluble state. As the result of assimilation by 
plants inhabiting hard water, the carbonic acid is absorbed and the 
insoluble calcium carbonate precipitated. It is this precipitate that 
forms the incrustation on the plants. The lime incrustation on the 
stones of the shore is formed by minute lithophilous Algae, in the 
process of their metabolism, in a similar manner to that by which the 
same substance is deposited on the stems of aquatic phanerogams. I 
have only seen similar lime-incrusted stones at one other place in 
Scotland, namely, Rescobie I^och in Forfarshire, but the phenomenon 
probably occurs wherever lime is abundant. 
The lime-incrusted Characeae are extremely abundant in the 
lochs of Lismore, and carpet the bottom with dense masses of their 
brittle shoots, from the margin down to 40 feet deep. When a boat 
is brought near the shore, one can hear the Chara grating upon her 
bottom with a rasping noise. Besides the showers of lime flakes 
that are continually falling from living aquatic vegetation, after the 
death of the plants any remaining lime incrustation will be broken 
up and it, too, deposited upon the bottom of the loch. In this way 
a lacustrine deposit of lime is being laid down at the bottom of these 
lakes, mixed with diatoms and other organic remains. The analysis 
of the water proves it to be rich in plant food-salts, and this is borne 
out by the exuberance of the vegetation. 
