172 Proceedings of the Eoyal Society of Edinburgh. [Sess. 



in the water of the loch. The water is fairly clear, and is 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, which is particularly the 

 case along the east side, it is usually carpeted with Chara aspera, or its 

 var. subinermis, and sometimes with C. vulgaris and C. fragilis, to a depth 

 of 14 or 15 feet. The growth of these plants, particularly the first men- 

 tioned, at depths 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 at 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, as, for 

 example, in some places at the west side of the loch and in the bay at the 

 east end of St Serf's Island, Anacharis Alsinastrum grows with such 

 extraordinary vigour that in the summer, when the 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 everywhere. This mud, which is usually 

 blackish, with a somewhat offensive odour, was in August crowded with 

 worm-like larvse 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 was extremely 

 abundant, and that it had been partially exterminated by the former plant. 

 Besides those already mentioned, the following plants occur at this loch : — 

 Littorella lacustris, Callitriche autumnalis, Heleocharis acicularis, Tolypella 

 glomerata, but very scarce; Myriophyllum spicatum, M. alterniflorum, 

 Potamogeton filiformis, P. pusillus, P. obtusifolius, P. heterophyllus, and in 

 pools on the shore the var. terrestris, Schlecht., P. prselongus, P. Zizii, P. lucens, 



* It is supposed that this plant was introduced into Loch Leven by an itinerant hawker 

 of gold-fish, who, changing the water in his tanks at the loch, threw out some of the plant. This 

 is quite possible, as Anacharis is commonly used for aerating the water in aquaria, and la 

 sold by dealers for that purjjose. In non-peaty water containing a supply of suitable plant 

 food-salts the smallest scrap of this plant bearing a whorl of leaves will grow and increase 

 very rapidly, whether floating or attached to the bottom. That the Anacharis has not 

 become general at other non-peaty lochs of this Area is probably because (1) it propagates 

 vegetatively, as only female plants occur, consequently no seed is produced for disijersal by 

 birds ; (2) the form of the plant is such that it is not likely to be carried inadvertently on 

 the legs or bodies of birds ; (3) the only effluent of Loch Leven flows directly into the sea 

 without entering any other loch. 



