DR. G. S. WEST ON THE ALGÆ OF 
18 
DoMINANT FORMS AND THEIR PERIODICITY. 
Flagellata.—T wo species and two varieties of the genus Dinobryon formed 
They attained their maximum very 
a characteristic part of the plankton. 
March, with a water-temperature of 18°-20° C. All the forms disappeared 
rapidly, occurring in abundance from February (or even December) to 
with equal rapidity, and were entirely absent from May to October. The 
occurrence of Dinobryon only in the warmer part of the year 13 а fact which 
In the British lakes this genus reaches its 
calls for special mention. 
Fig. 3. 
3 | ЕВ. | МАҢ. APR.| MAY | JUNE JULY | AUG. SEPT. | OCT. | NOV. | DEC.| JAN. РЕВ. y 
3 1905. 1906. i 
| 17.8° | 183° | 17-8" 18-9° | 12-2°| 10-0 |10-0* | 10-0" | 1227 | 15-0° 20:0 25'3° 24-4") À 
ссе T TU kee 
E Ba 
LL] H ae = 
\ Wal ffe 
\ ^, 
ве \ / N ec 
\ 
\ А \ 
\| 4 m 
1 р \ 
c Y і | е 
yi I 
—— H — 
tu | 
А 
r IW r 
M 
— fh — 
H | \ 
t \ 
тт i H rr 
i d 
I——34 / M || 
r \ 
N || X 
4 MN 
rrr| — F —7 NL rer 
| 
DESMIDS MELOSIRA GRANULATA --------- 
DINOBRYON — — — — CRUSTACEA `  ———————- 
Chart showing the periodicity of the dominant constituents of the Yan Yean plankton. 
The relative frequency is indicated by the same lettering as in the Table of Phytoplankton. 
maximum in spring, generally in May, at a time when the temperature of 
the surface-water is little more than half the average summer temperature. 
This;is in agreement with the observations of Tanner-Fullemann on the 
oceurrenee of Dinobryon in certain of the Swiss alpine lakes *, and Ostenfeld 
* M. Tanner-Fullemann, in {Bull. de Нет. Boissier, 2те sér., vii. (1907) р. 226 
[ Мах, development in May with a water-temperature of 11° C.] 
