30 
William J. Hodgetts 
(a monthly mean between 4 0 and n° C.), higher summer-tem¬ 
peratures being very unfavourable. Low or moderately low con¬ 
centrations of the water (10 to 17 degrees) must obtain for growth 
to take place; and its development is conditioned by the presence 
of a suitable quantity of the "host” (the wide sterile species of 
CEdogonium). 
Nitella flexilis (Section XV) apparently develops most rapidly 
when the temperature is moderately high (a monthly mean between 
9 0 and 14 0 C.); and abundant bright sunshine, although not essential 
for purely vegetative growth, is very necessary for oospore-produc¬ 
tion. No relation to the concentration of the water is shown. The 
growth of the endophytic Coleochcete Nitellarum was always limited 
by the somewhat local growth of its "host,” but abundant sunshine 
is essential for the production of the sexual organs of this endophyte. 
The various species of the Protococcales (Section XVI) which 
have been at all abundant in the pond form a sort of series as regards 
the temperature most favourable for their development. On the one 
hand Ankistrodesmus falcatus requires a monthly mean temperature 
between n° and 14 0 C., while the higher summer-temperatures 
appear to be unfavourable, and on the other hand Pediastrum 
Boryanum and P. tetras are adapted to the highest summer-tem¬ 
peratures, while Scenedesmus denticidatus var. linearis and Dictyo- 
sphcerium are intermediate as regards their behaviour towards 
temperature. All (except Pediastrum) seem to develop best with 
moderately high concentrations between 16 and 20 degrees. Pedias¬ 
trum shows no relation to the concentration of the water. 
Chlamydomonas Reinhardi (Section XVII) tends to develop best 
in the pond during late summer and early autumn (September), 
when the temperature is falling (monthly mean temperature between 
16-5° and I3°C.). A high or rather high concentration (18 to 27 
degrees) favours growth, and the species is probably mixotrophic in 
its nutrition in nature. Chi. Debaryana and Chi. monadina are also 
apparently favoured by the presence of organic compounds in the 
water, but are adapted to lower temperatures than Chi. Reinhardi. 
Pandorina and Eudorina (Section XVII) both tend to have their 
periods of growth during the summer-months (May—August) 
although Eudorina generally persisted in some quantity well into the 
autumn, and was generally rather more hardy than Pandorina. The 
behaviour of both species during the summer-months was very 
variable and was probably the result of mutual competition, and 
perhaps also competition with other algae. 
