114 Proceedings of the Royal Society of Edinburgh. [Sess. 
the water, but because in deeper and often in shallower water too, the 
bottom is very rocky. I have noticed in many lochs that a rocky bottom 
is nearly always destitute of the higher plants, that is, when the bottom 
could be seen or felt with a pole having teeth at the end, or with a weight 
attached to a line. By bumping such instruments over the bottom of a 
loch the vibrations carried to one’s hand up the wood or cord give an 
indication of the constitution of the bottom — mud, sand, gravel, rock, etc. 
Dredging over a rocky bottom is, of course, impossible, leaving out of the 
question the certainty of losing the apparatus. The reasons for a rocky 
bottom within the photic zone being either devoid of plants or supporting 
very few are probably — (1) want of a suitable substratum in which the 
plants may root ; (2) because of the scarcity of plants, the refuse-eating 
organisms at the bottom are able to deal with all the organic remains that 
reach them, so that nothing is left but the excrement of such creatures ; 
this, in turn, is attacked by bacteria, and by these means the rocky bottom 
is kept clean instead of being covered with mud. A general view of this 
loch is given in fig. 16. 
Loch Fleet is a somewhat oval sheet of water situated about a mile 
east of Loch Grennoch, and surrounded by treeless hills, excepting on the 
south-east. It is about 4 mile long by J mile wide, 56 feet deep, and 1113 
feet above sea level. The margin is rocky, and there is very little shore 
suitable for the development of littoral Phanerogams. The water is clear 
and but slightly peaty. The scanty flora is restricted to the common types 
found at Loch Grennoch. 
Loch Skerrow is situated amongst wild, rocky, moorland scenery, 
4 miles east of Loch Grennoch at an elevation of 414 feet above sea 
level. It is a shallow, somewhat triangular loch f mile long with a very 
rocky shore (fig. 18), and clear, slightly peaty water. Its maximum depth 
is 33 feet, and the bottom is mostly covered with rocks which frequently 
rise above the surface of the water. The larger of these island-rocks are 
capped with vegetation of the moorland type, such as Calluna vulgaris, 
Vaccinium Myrtillus, etc. (fig. 17). More numerous are the rocks which 
rise to just below the surface of the water. These necessitate caution in 
navigating a boat, and obviously such a rocky bed greatly hinders 
dredging operations. Sandy portions of the bottom to a depth of 12 feet 
bore an abundant vegetation, but of a limited variety ; otherwise there was 
little to be noted, excepting at the margins and in shallow, sheltered bays. 
The submersed plants were — Littorella lacustris, Lobelia Dortmanna, 
Isoetes lacustris, Subularia aquatica, Juncus fluitans, Myriophyllum 
alterniflorum, Nitella opaca, Chara fragilis, var. delicatula, Fontinalis 
