1904 - 5 .] Study of the Lakes of Scotland and Denmark. 423 
Danish lakes, while, on the other hand, many forms found in the 
Danish lakes have not hitherto been observed in the Scottish 
lakes. I may here give a short account of the commoner 
plankton-forms, based on the investigations above referred to. 
The Cyanophycea play an altogether inferior part in the com- 
position of the plankton in the larger Highland lakes, the only 
rather common forms being Anabcena flos aqua, and Coelosphcerium 
ncegelianum. With regard to Lyngbya and Oscillatoria further 
explorations may give information, but as Mr Murray often speaks 
of “ filamentous Algse in abundance ” they are probably common. 
Of the Diatoms, it may be pointed out that Melosira, as in 
many other mountain lakes, seems to be relatively rare, and 
never forms those huge masses of plankton found in the Danish 
and other lowland lakes. Stephano discus astrcca has not yet been 
observed as a plankton-organism ; and Cyclotella , which has often 
been considered as characteristic of alpine lakes, was not so common 
as might have been expected, yet I suppose that closer examina- 
tion at other seasons may prove that it is abundant ; Fragilaria 
crotonensis also seems to be rare in the Scottish lakes. The 
commonest forms are : — Asterionella gracillima, Tabellaria fenes- 
trata, var. asterionelloides , T. flocculosa (in chains), and a remark- 
ably large number of bottom and shore Diatoms (Naviculoidese and 
Surirelloideee). 
With regard to the Chlorophycea, Chodat has observed that 
nearly all the small forms belonging to the Euchlorophycea are 
warm-water plants, having their home in small ponds, the water 
of which is rich in disintegrated organic matter ; in the Pelagic 
region of the greater lakes they are nearly all rare, and must be 
considered as merely chance visitors, introduced by streams and 
rivers, soon finding their graves in the Pelagic region of the lakes : 
to this rule we find only a few, but very peculiar, exceptions. 
A study of the Chlorophycea in the Danish lakes has shown this 
view of Chodat’s to be quite correct : as all our lakes are shallow, 
and the water in summer very warm, they should, according to 
Chodat, be extremely rich in Chlorophycea, and this is exactly 
the case. With regard to the Scottish lakes, we find some very 
remarkable features. All the Euchlorophycea seem, from my own 
observations, to be rare, and Messrs West (1904, p. 554) have 
