1000 Proceedings of Royal Society of Edinburgh. [sess. 
indispensable to most plants are poison to others. In the area of 
Lochs Ness and Oich there is but a small amount of soil rich in 
food-salts available for drainage, compared with the soil poor in 
food-salts and rich in acid humus. Consequently the effect of 
drainage from a small, rich food area is almost extinguished by 
the humic acids, and in such lowland lochs we find vegetation 
identical with that of the highest mountain lakes. Again, in 
Lochs Oich and Ness (and of course others) we have practically 
no reedy margin, neither have we in many mountain lakes. The 
reason for this is the nature of the shore, combined with the 
erosive power of the waves, leaving altogether out of the 
question food supply. On the other hand, in mountain lakes with 
a sheltered peaty or muddy shore, as in lowland lochs of like 
nature, we find a reedy or sedgy margin. The most luxuriant 
sedge association (Carex rostrata) that I have seen was at an 
elevation of 2300 feet ; but the factors are there suitable. Phrag- 
mites communis and Scirpus lacustris I have seen abundant at 
800-1000 feet elevation. Highland lochs are usually in situations 
fully exposed to the fierce winds, their shores rocky or stony, 
consequently they have few plants about their margins. Their 
water, being poor in food-salts and rich in humic acids, has a 
restricted aquatic flora; but the same conditions may obtain in 
the lowlands, when the flora of the lakes will be similar. On 
the other hand, a highland loch having a supply of food-salts, with 
a suitable shore, and sheltered from prevailing winds, may quite 
well have the character of a lowland loch regarding its flora. 
Lochan Coire Glas, in Glen Garry Forest, is an extremely wild 
little lake about 1600 feet above sea level. Mountains rise 
precipitously from its margin to over 3000 feet, closing it in on 
three sides like an amphitheatre (fig. 43). Gusts of wind 
descending the mountains strike the loch with terrific force, not- 
withstanding its apparently sheltered position. This loch is 
gradually being silted up with detritus washed in by the burns, 
or rather waterfalls, that descend the mountains. A sand-bank 
in the middle of the loch is covered with Heleocharis palustris. 
The following plants also occur here : — Callitriche hamulata, Juncus 
lluitans, Myriophyllum alterniflorum, Isoetes lacustris, Littorella 
lacustris, Potamogeton natans, P. var. app. polygonifolius, 
