ee Ee Pe ee ee ee ee ee ee ees mats Se -. ee eee Op eee ee ee See a ee ee. are 
- ve 
176 MISSOURI BOTANICAL GARDEN, 
reaching its climax in December. How much these depend 
upon gas content and how much on temperature and nitro- 
genous content is not fully established. Temperature is 
known to be an important factor. 
Horation Parker (’11) found that Synwra appeared in 
Lake Chochituate with a temperature of 48° to 50° F. and 
disappeared when the temperature fell below this. But he 
says: “Temperature is not the only factor that fostered 
the organisms at this place (the thermocline), for at higher 
levels (above the thermocline) there would have been less 
free carbonic oxide, and at lower ones less oxygen and less 
sunlight.” 
Marsh (’08) found Synedra in Green Lake, Wis., in 
nearly every month in the year, but in one winter especially 
it was flourishing from January to May. This fact, while 
difficult to reconcile with a part of Parker’s theory, confirms 
his statement in another that the temperature is not the 
important factor. Fritsch (’07) also believes that the 
scarcity of diatoms in tropical waters is due to the small 
amount of dissolved gases in the water, rather than to an 
unfavorable temperature, though, in general, they prefer 
colder water. 
Studies made by Whipple and Parker (’02) in previous 
years and also by Baldwin and Whipple (’06) furnish, in 
a degree, the lacking proofs and serve to confirm the con- 
clusions of Parker as to the relative importance of these 
dissolved gases for phytoplankton in general. The studies 
of Marsh (’03) serve, also, in a way, to confirm this idea; 
for while Whipple and Parker (’02) found diatoms, such 
as Synedra, Melosira and Cyclotella, reaching their maxi- 
mum in spring and summer, as Marsh did in Lake Winne- 
bago, yet he finds it to occur in Green Lake in the depth 
of winter, for three successive winters. He quotes Voigt, 
also, as reporting the maximum for Asterionella as occurring 
in winter in Traumer-See and Edeberg-See. This would 
indicate that temperature is not the deciding factor. 
Whipple and Parker (’02), in the studies above cited, 
describe a large growth of diatoms just below the thermo- 
