FLOKA OF SCOTTISH LAKES 
259 
as well as of Heleocharis palustris and Equisetum limosum, that enter 
the water here and there ; otherwise there are no plants of the semi- 
aquatic type in the water of the loch. The water is fairly clear, 
and not appreciably peaty. The bottom of the loch, from the shore 
to a depth of about 15 feet, consists largely of firm sand, which is, 
however, frequently dirty and mixed with mud. Where the bottom 
is of this nature it is usually carpeted with Chara aspera, or its var. 
subinermis, to a depth of 14 or 15 feet. The growth of these plants 
at a depth of from 4 to 8 feet is prodigious, but they thin out 
towards the shallower water on the one hand, and towards the deeper 
water on the other. Nitella opaca occupies considerable areas, also 
where the bottom is sandy, and at similar depths to the Chara, but it 
has a tendency to be most abundant in slightly deeper water than 
that in which the maximum growth of the Chara occurs. On the few 
areas where the bottom, from near the margin to a depth of 15 feet, 
is of mud — for example, at the west side of the loch and in the bay at 
the east end of St Serfs Island — Anacharis Alsinastrum grows with 
such extraordinary vigour that in the summer, when these plants are 
near the surface, it is very difficult to row a boat through them. At 
greater depths than about 16 feet no living vegetation of the higher 
type occurs, and mud covers the bottom nearly every w^here. This 
mud, which is usually blackish with a somewhat offensive odour, was 
in August crowded with worm-like larva? at many parts of the loch. 
Among a number of other plants which grow in the water the most 
abundant is probably Potamogeton perfoliatus. The boat- keeper at 
the loch informed me that, previous to the extensive development 
of the Anacharis, this Potamogeton w^as extremely abundant, and 
that it had been partially exterminated by the former plant. A 
considerable number of plants grow at this loch, amongst which the 
following are not of frequent occurrence in Area VII. : — Carex aquatilis, 
C. hirta, which grows on the sandy shores like C. arenaria on the sea- 
shore, Alisma ranunculoides, Lysimachia nummularia, and Ranunculus 
reptans. A few Bryophytes occur in marshy places, but are not 
abundant, excepting on parts of the south shore. 
The Isle of May is situated at the entrance to the Firth of Forth, 
and I was induced to visit this isolated spot in order to investigate a 
small loch which is there, thinkins; it mio;ht afford somethine^ of interest 
because of the numerous water-birds that visit the island during their 
migrations. The loch, which is quite small, is situated in a ravine 
that divides the island obliquely in the direction S.E. by E. and 
N.W. by W. From the rocky and precipitous nature of the ravine 
one might imagine the pool to be a little lochan high on the 
mountains. The extensive engine-house at the east end, and the 
cement dams at both the east and west ends, however, quickly dispel 
