PERIODICITY OF THE PHYTOPLANKTON OF SOME BRITISH LAKES. 403 
Windermere this organism attained its maximum in August, but persisted т 
very small numbers from September to December. 
Ceratium Hirundinella had two maxima—a small one from June to July, 
and а more pronounced one from September to October. 
2. WasTWATER, CUMBERLAND. 
This is the deepest of the English lakes, having an average depth of 
135 feet and a maximum depth of 258 feet. It is about three miles in 
length by about half а mile in breadth, and is 204 feet above sea-level. Тһе 
drainage is received from the western side of Scafell (3162 feet) and Scafell 
Pike (3210 feet), and from the southern slopes of the Steeple, the Pillar, and 
Kirk Fell. The lake contains a large volume of water, and is practically 
free from all contamination. The collections were made at approximately 
monthly intervals from August 1908 to July 1209. 
Ана. Ath, 1908. Temp. of water 68° Е. (—17T2* C). The dominant 
constituent of the phytoplankton was Staurastrum jaculiferum, A few other 
Desmids were present, but on the whole the amount of phytoplankton was 
ather small. Peridinium ИШе was common. Rotifers were numerous 
and Copepods abundant. 
Sept. Sth, 1908. Temp. of water 51° К. (=10°5° C.). Plankton not 
unlike that of previous month, with Staurastrum jaculiferum dominant. 
Rhizosolenia morsa and Spherocystis Schroeteri both common. Rotifers 
numerous. Copepods abundant. 
Oct. 5th, 1908. Temp. of water 60° Е. (= 15:5? €.). Phytoplankton not 
unlike that of September, with some abundance of Staurastrum jaculiferum, 
One of the most noteworthy Desmids was Genicularia elegans. Sphærocystis 
Schroeteri and Rhizosolenia morsa were both exceedingly abundant. Rotifers 
very abundant. Copepods few. 
Nov. 4th, 1908. Temp. of water 54° F. (—12:2? С). Phytoplankton 
very similar to that of October, with the same dominant species. Genicularia 
elegans also occurred again. Rotifers very abundant. 
Dee. 3rd, 1908. Temp. of water 48° F. (= С). Great reduction in 
quantity of Splurrocystis Schroeteri and slight diminution in Staurastrum jacu- 
liferum, but considerable increase in Zihizosolenia morsa, which attains its 
maximum abundance in this month. Rotifers abundant. Few Entomostraea. 
Jan. 4th, 1909. Temp. of water 46? Е. (= 8^ C.). The numbers of 
Staurastrum jaculiferum further reduced, and also a considerable falling off 
in Rhizosolenia morsa. Peridinium Willei had become frequent. Large 
Copepods were the dominant feature of the plankton. 
Feb. Sth, 1909. Temp. of water 49° Е. (5:5° C). Staurastrum Jaculi- 
ferum still further reduced in numbers. Diatoms more numerous, especially 
