1909- 10.] Flora of Scottish Lakes. 165 
substance. At other places upon this side of the loch the shore is gravelly 
or sandy, and hears more plants than the opposite side does. The chief 
affluent enters the loch at the west end, previous to which it has a very 
sinuous course for about a mile through an alluvial flat consisting of pasture 
or arable land, doubtless at one time covered by the water of the loch. 
Near the loch this flat merges gradually into a bog several acres in extent 
(fig. 104). At the east end, whence flows the effluent, and where also another 
burn enters the loch, there is a similar but much less extensive bog (fig. 105). 
The loch is shallow throughout its area, a depth of 10 feet being seldom 
exceeded. The deepest water occurs opposite the mine on the south shore, 
where a depth of 17 feet may be sounded ; this depth is probably due to 
the bottom sinking on account of the mining operations below. The photic 
zone extends to a depth of 12 feet, beyond which black mud occurs and no 
living vegetation. The stones about the shores are nearly everywhere 
thickly covered with Cladophorae, which bear an extraordinary quantity of 
Diatomacese, chiefly of the genera Diatoma, Gomphonema, and Cocconeis. 
A remarkable feature is the vast amount of Potamogeton pectinatus growing 
in water from 6 to 12 feet deep, the slender stems carrying the flowers to 
the surface even from the greatest depth. Here and there at the marshes 
are pure groups of Iris Pseud-acorus, with leaves 4 or 5 feet high, standing 
out of the water as little islands. A considerable portion of the bottom is 
covered with Chara fragilis and its vars. fulcrata and delicatula, C. aspera 
and its vars. subinermis and capillata, and C. contraria, as well as with a 
number of other plants. Litorella lacustris and Heleocharis acicularis are 
scarce. Callitriche autumnalis is very abundant ; besides the type there is 
a form differing slightly in the leaves and fruit. About the marshes 
aquatic and terrestrial forms of C. stagnalis abound. Potamogeton 
rufescens, the type as well as a very leafy, barren form, is abundant. 
P. pusillus, the type as well as a narrower-leaved form, P. filiformis, the 
type and a much longer-leaved form, and P. pectinatus are all very 
plentiful; indeed, the three last-mentioned species are so abundant that 
their fruits, which in the autumn are washed upon the shore, formed in 
a few places a stratum over the sand an inch deep. Potamogeton 
perfoliatus, P. Zizii, and P. obtusifolius are all very abundant, while P. 
preelongus, P. natans, and P. polygonifolius are all scarce. Myriophyllum 
spicatum is very plentiful, but M. alterniflorum is scarce. Anacharis 
Alsinastrum occurs sparingly, and the plants are weak. The following 
also occur, but none of them is abundant : — Nitella opaca, Juncus fluitans, 
Ranuncubis peltatus, Nymphsea lutea, Polygonum amphibium, Sparganium 
simplex, var. longissimum, the last near the affluent at the west end, and 
