24 
William J. Hodgetts 
4 
Table showing the Occurrence of Three Flagellates in Hawkesley 
Hall Pond during 1918-1921. 
d 
cj 
i—> 
•s 
Ph 
Mar. 
Apr. 
May 
June 
j>» 
"3 
1 —> 
Aug. 
Sept. 
0 
O 
> 
0 
6 
V 
Q 
1 
f 1918 
vr 
vr 
vr 
r 
rr 
rr 
rr 
rc 
rr 
rr 
r 
r 
Cryptomonas j 
1 1919 
vr 
vr 
vr 
r 
vr 
vr 
rr 
rr 
rr 
r 
rr 
rr 
ovata j 
1 1920 
vr 
vr 
vr 
r 
r 
r 
r 
rc 
rr 
vr 
vr 
vr 
[1921 
vr 
vr 
vr 
r 
r 
r 
| 
(1918 
vr 
vr 
r 
r 
rc 
rc 
r 
r 
r 
r 
r 
vr 
Trachelomonas J 
| 1919 
vr 
vr 
r 
rr 
rr 
r 
vr 
rr 
vr 
vr 
vr 
vr 
volvocina j 
1 1920 
vr 
vr 
r 
rr 
rr 
rc 
rr 
rc 
rr 
r 
vr 
vr 
1 
U921 
vr 
vr 
vr 
vr 
r 
r 
(1918 
_ 
_ 
vr 
vr 
r 
rr 
vr 
Trachelomonas J 
) 1919 
— 
— 
— 
r 
rc 
r 
vr 
vr 
— 
— 
— 
vr 
hispida 
| 1920 
vr 
vr 
vr 
rr 
r 
r 
vr 
rr 
rr 
vr 
— 
— 
U921 
— 
— 
— 
vr 
vr 
r 
“rather rare” without showing much relation to temperature (cf. 
its slight development November—December 1919). The species was 
always poorly represented during the winter and early spring. High 
or rather high concentrations of the water are decidedly favourable, 
rapid growth always coinciding with a concentration between 17 and 
21 degrees, and still higher concentrations (August and November 
1919—cf. Fig. 3) are far less unfavourable than lower ones, in fact 
low concentrations, especially when combined with low temperatures, 
are obviously verjr antagonistic towards the growth of this species. 
No relation to bright sunshine is apparent. 
Trachelomonas volvocina (cf. table above) exhibits a rather 
puzzling periodicity, which is not closely related to temperature- 
conditions, although the lower temperatures of winter are clearly 
unfavourable. Growth commences earlier in the year than with 
Cryptomonas, and the maximum is also reached earlier (often in 
spring), and sometimes there is a secondary maximum in August 
(1919, 1920), while the species is generally rare during the autumn 1 . 
Its occurrence in the pond appears to be best explained by reference 
to bright sunshine (Fig. 2) and the concentration-data (Fig. 3). Of 
the five maxima observed, three (May—June 1918, August 1919, 
June 1920) occurred in very sunny months, and also when the 
1 Kofoid (22) found that T. volvocina was best developed in the plankton 
during the warmer summer months. On the other hand Fritsch and Rich (18) 
found that this species had its maxima frequently at the end of winter or 
during early spring, although at other times the maximum of T. volvocina and 
T. hispida coincided with the warmer months of the year. 
