280 The Upper Elf Loch, Braids. [Sess. 



Thus near the north-west end there is a somewhat luxuriant 

 growth of the common rush and the pretty bog-bean, with such 

 less conspicuous plants as the vernal starwort, the Canadian 

 poncl-weed or Anacharis, the water-crowfoot, and the duck- 

 weed or Lemna — this last -mentioned plant covering large 

 spaces with its minute leaves. At the south-east end the 

 surface of the loch is covered with the yellow water-lily and 

 the common pondweed or Potamogeton. The loch itself, 

 though situated in a natural hollow, is free to the sky, not 

 surrounded by trees, well covered with vegetation, and in a 

 quiet, retired spot, not liable to be much disturbed. At night 

 it is much frequented by wildfowl, and Mr Speedy informs 

 us that he has often shot wild-duck here by moonlight, from 

 the covert of the whin-bushes overlooking the loch. From 

 the first survey of it, as already said, it was believed that it 

 would yield good results for microscopists, and that these 

 expectations have not been disappointed we shall now proceed 

 to show. 



Beginning with the motile alga? (Volvocinese), there are 

 present such forms as Chlamydococcus, Gonium, Stephano- 

 sphaera, Pandorina, and Volvox. These are most interesting 

 plants, and very beautiful under the microscope. But perhaps 

 the last named, Volvox globator, or the "Polling sphere," 

 is the most familiar form, and a few remarks regarding it 

 may be given, as we have here the full differentiation of 

 sex. The life-history of this interesting plant, through its 

 various stages, was followed throughout the year. In the 

 asexual or vegetative form of reproduction — the usual method 

 of multiplication in Volvox — the mature plant simply breaks 

 up and sets free the component " zoosporanges," and this 

 may — and, indeed, generally does — go on throughout the 

 year. But in the sexual generation, which begins in autumn, 

 certain cells become changed into sperm-cells and others into 

 germ-cells, both remaining for a time within the Volvox 

 sphere, which is thus monoecious. From these two kinds of 

 cells oospores are formed, and when these reach maturity the 

 parent cell breaks up and the oospores fall to the bottom, 

 where they remain all winter. In spring, with the advent of 

 mild weather, the Volvoces " swarm," as it is termed, swimming 

 actively about on the surface ; but as the summer proceeds 



