THE FRESHWATER .PLANKTON OF THE SCOTTISH LOCHS. 55) 
slight. This absence of any marked variation in character is to be attributed to the 
relatively slight changes in the temperature of the surface waters at different seasons. 
2. The greater part of the phytoplankton consists of Chlorophycece, and the major 
. portion of these belong to the Conjugate. Most of the filamentous Alge of the 
plankton are Conjugates. 
3. The plankton contains a rich Desmid-flora. 
4. This Desmid-flora owes its existence to the Older Palzozoic and Precambrian 
formations of the areas in which the lakes are situated. This rich Desmuid-flora rs not 
an isolated phenomenon peculiar to the plankton of the Scottish lochs, but it is also 
found in the plankton of those lakes of the Englsh Lake District, N. Wales, and 
W. Ireland which are similarly situated on the Older Palxozoic formations. The 
abundance of Desmids is due to the absence of lime and the presence of humic acid in 
the water, these conditions being rendered possible by the geological nature of the 
areas in question, which are suitable for the formation of peat-bogs and peaty pools. 
The diversity of the Desnud-flora and the presence of some of the handsomest species 
of the family appear to be directly connected with the antiquty of the geological 
formations. 
5. The Desmid-flora differs essentially from that of the small peaty pools and bogs 
of the same area, especially in the relative abundance of the species common to both 
the bogs and the plankton. 
6. The Desmids were doubtless originally derived from the pools and bogs of the 
mountains, and only those species have flourished which found the conditions most 
suitable for their existence as pelagic organisms, some of them having in course of 
time produced distinct and characteristic plankton-varteties. 
7. There is no very obvious maximum development of Diatoms, and some of the 
larger species of the Naviculoider and Surirelloidex have firmly established 
themselves. 
8. The proportion of Myxophycex is relatively small, and species of Oscillatoria, 
Lyngbya, and other genera are somewhat scarce. 
