ene age apres tk ol a 
RELATION OF ALGAE TO DISSOLVED GASES. 183 
sponding regions in Scotland. As regards the organisms 
themselves, the Cyanophycee play a very much less im- 
portant part in Scotland than in Denmark, while conversely, 
the desmids are remarkably well represented in the plankton 
of the Scottish lakes and but feebly so in the Danish lakes, 
in common with nearly all central European lakes. 
West (04) notes that “Desmids thrive best in soft water, 
and they are most numerous in peaty water which has a trace 
of acid. With few exceptions they do not flourish in water 
containing carbonates of lime in solution, and no good col- 
lection of desmids can be made in a purely limestone district 
in which the water is hard.” 
Fritsch (’07) thinks that the scarcity of diatoms in trop- 
ical waters, noted especially at Ceylon, is due to the small 
amount of dissolved gases in the waters, and not to the high 
temperature, per se, except in so far as it influences the 
amount of dissolved gases. He found them only in aérated 
waters, i. ¢., running streams. He did not have data as to 
the amount of dissolved gases, but assumes a prior that a 
high temperature, 25° C., must of necessity indicate a low gas 
content, as indicated by figures from Forel’s tables. The 
lowest temperature attained by the lowland waters of Ceylon 
was 25° C., which in the table corresponds to 5 ce. of oxygen 
per liter. 
Temperature Oxygen CO, 
Per liter of water,as 
Forel Aas A i aa ae o- found in the waters 
: : of Lake Geneva. 
ea 5° C. 8.68 Standard. 
ae 20: 6.28 Saturation. 
In the fish-pond, mentioned as an example of temperate 
zone fresh water, near Bristol, England, Fritsch (’09) finds 
that diatoms play an important part. The free forms pre- 
dominate during the winter months, but are rare during the 
summer months and occasionally absent. The water in this 
locality and latitude does not become very strongly heated, 
