PERIODICITY OF THE PHYTOPLANKTON OF SOME BRITISH LAKES, 
419 
The phases of the plankton of Loch Katrine, although distinct, are difficult 
to demarcate. 
follows :— 
I. December—Mareh (cold period, with continuous fall in temperatu 
re). 
Amount of phytoplankton small. Minimum of Chlorophyce: ^ ( 
rapid diminution of Celospherium up to the middle of March. 
It seems best to subdivide the year into three periods, as 
ind 
After February, Desmids and Peridinium Wille? begin to increase 
rapidly. 
to February, and then disappears. 
Rhizosolenia morsa has a first maximum from December 
Fia. 4. 
AUG.| SEP | OCT. | NOV. | DEC. | JAN. | РЕВ. | MAR. | APR. | MAY | JU JY. 
1908. 1909. 
È |15-5° | 13:5° | 12°79] 10° | 72? | 6:31? | 44° | 5-9°| 7.7° T7? | 12.2? |15-5°| | 
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STAURASTRUM JACULIFERUM forma PERIDINIUM WILLE! = 6-6-6 
TRIRADIATA CELOSPHALRIUM KÜTZINGIANUM 20000000000 
ST. PARADOXUM (type) —-—-—---—--- RHIZOSOLENIA MORSA +++ ++ ++ 4444 
Chart of the periodicity of five of the dominant constituents of the phytoplankton 
of Loch Katrine. The temperatures are in degrees Centigrade. 
П. April—July (continuous rise in temperature). 
Desmids and in Peridinium Wille. 
striking Desmid-plankton. 
Great increase in 
In June and July there is a 
Jühizosolenia morsa appears again 
abundantly in June, and attains а second maximum in July. 
Celospherium rapidly increasing in amount. 
