PERIODICITY OF THE PHYTOPLANKTON OF SOME BRITISH LAKES, 415 
Dec. 15th, 1908. Temp. of water 45° Е. (= 72° €.). Staurastra still 
numerous, Very little Calospheriun, but a great increase in amount of 
organic detritus. Sterile Gtdogonium still common, Khizosolenia morsa 
fairly frequent, and other Diatoms becoming evident. First appearance of 
the coiled Lyngbya contorta. 
Jan. 18th, 1909. Temp. of water 43° F. (=6°1° C.). Staurastrum para- 
dogum still fairly common, Corlospherium distinctly rare and colonies in 
very poor condition. Much fine detritus and few Diatoms. Lyngbya contorta 
not uncommon. Entomostraca and Nauplii very rare. 
Feb. 16th, 1909. ‘Temp. of water 40° Е. (—44? C.). Very similar to the 
January plankton, but with a larger quantity of Lyngbya contorta. 
March 16th, 1909. Temp. of water 39° К. (—3:9? C.). Staurastra becoming 
more numerous, and also considerable increase in Cosmarium abbreviatum var. 
planetonicum. All the Desmids showing active vegetative division. Diatoms 
uncommon. Much detritus; few Rotifers ; and no Entomostraca. 
April 18th, 1909. Temp. of water 46° F. (2 71? C.). Desmids numerous, 
especially Staurastrum. Corlospherium decidedly increased, and Diatoms 
not uncommon. Rotifers rare ; few Nauplii. 
May 18th, 1909. Temp. of water 46° F. (— 771? €C.). Desmids numerous, 
especially the typical form of Staurastrum paradowum, No increase in 
quantity of  Celospherium. Diatoms moderately abundant. Lyngbya 
contorta entirely disappeared. Rotifers few ; Nauplii very numerous, 
June 17th, 1909. Temp. of water 54° F. (—12:2? €C.). Great increase in 
number of Desmids, so that the plankton has now become a Desmid- 
plankton, largely composed of a few species of the genus Staurastrum. The 
Chlorophycee have reached their maximum, and the Diatoms, although 
numerous, are not conspicuous. PRhizosolenia morsa іх again common, and 
the frustules are considerably wider than in the preceding November and 
December. Few Rotifers ; Nauplii and Crustacea practically absent. 
July 16th, 1909. Temp. of water 60° F. (=15:5° C.). Plankton rather 
similar to that of preceding month. Still а Desmid-plankton, but various 
Chlorophycee aud Peridinium Willei much more numerous, so that the 
Desmids do not dominate to the extent that they did т June. Phizosolenia 
morsa abundant, and also a considerable increase in the quantity of Celo- 
sphorium Kiitzingianum. Few Rotifers. Bosmina longirostris not uncommon. 
Loch Katrine has a mixed plankton of Chlorophycee, Diatoms, and 
Мухорһусее. The total number of species observed from August 1908 to 
July 1909 was 63, of which 35 (or 55°5 per cent.) were СШогорһусеге, 16 
(ог 25°6 per cent.) Bacillariew, 1 (or 1:5 per cent.) Phæophyceæ, 8 (or 1278 
per cent.) Myxophyce, 1 (or L5 per cent.) Flagellata, and 2 (or 3-1 per 
per cent.) Peridinice. 
