102 Proceedings of the Royal Society of Edinburgh. [Sess. 



the antiseptic action of the peaty water, these remains do not readily deca}', 

 but accumulate from year to year and become spread out over the loch- 

 bottom in enormous quantity, and, of course, this stratum of dead grass, 

 wherever it lies, prevents the growth of a bottom flora. The depth to 

 which its influence extends varies somewhat in difterent lochs, and even in 

 any one particular loch. In Loch Doon, at the south end, where the loch 

 receives its principal supply of this grass from the rivers Gala Lane and 

 Carrick Lane, it spreads over the bottom to within 5 feet of the surface 

 of the water, and at other parts of the loch to about 7 feet below the 

 surface. From these deptlis it is spread over the whole loch-bottom more 

 or less. Even at a depth of 50 feet the dredge came up choked with this 

 deposit, which in such deep water is almost black, but not of a particularly 

 evil odour. The deposit of this substance in the loch must be the result of 

 the accumulation of many years, through the process of decomposition being 

 so slow in the peaty water. At Loch Stroan (p. 115) a large amount of 

 such dead grass is washed upon the east shore by the winter floods (tig 24). 

 Loch Stroan is a small, shallow loch, and in flood-time there is a very con- 

 siderable current passing through it from the River Dee, so that a portion 

 of the grass must be carried down the river into Loch Ken besides that 

 which is deposited high upon its own shore. Yet, notwithstanding these 

 losses, Loch Stroan has an abundant supply of this material on its bottom. 

 In the neighbourhood of Loch Trool there is much less grass available, and 

 the bottom flora of that loch extends to a depth of 16 feet (p. 112). 



The submersed aquatics that flourish in the available zone about tlie 

 margins of Loch Doon are as follows: — Subularia aquatica, Littorella lacustris, 

 Isoetes lacustris, Heleocharis acicularis, Nitella opaca, Fontinalis antipyretica, 

 vScirpus fluitans, Juncus fluitans. All the foregoing species are abundant 

 with the exception of the last mentioned, which, although plentiful in the 

 Gala Lane, is somewhat scarce in Loch Doon. Peplis Portula, a curious sub- 

 mersed form growing to a depth of 3 feet (p. 75), and Eurhynchium 

 rusciforme, at a depth of 3 to 5 feet (p. 93), were both very abundant 

 at the south end of the loch. The following were much less abundant : — 

 Lobelia Dortmanna, Myriophyllum alterniflorum, Sparganium natans, Chara 

 fragilis, var. delicatula, Batvachospermum moniliforme, and B. vagum. 

 Bryophyta and Algse other than those mentioned were extremely scanty, 

 and the paucity of plants in the marginal zone has already been referred to. 

 Figs. 1 to 3, with their respective descriptions, will aflbrd additional informa- 

 tion regarding the general features of this loch. The historic remains on 

 the island in tig. 2 will perhaps not be without interest to some readers. 

 The builders of this castle havino- constructed it centuries before the artificial 



