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 Avith mud. A general view of this 

 loch is given in fio^. 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 ^ mile long by I 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 slightl}^ peat3\ 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 | 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 Mja^tillus, 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 



