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OY SER OC ree ee 
188 MISSOURI BOTANICAL GARDEN. 
from 3.3 cc. per liter, June 23, to the saturation point of 7.80 
on July 20, when the “water-bloom,” consisting mostly of © 
blue-greens, chiefly Anabaena circinalis, Clathrocystis aeru- 
ginosa and Coelosphaerium Kuetzigianum, appeared. At 
the same time the water had changed from neutral through 
slightly alkaline to 5 cc. alkalinity during the same time, and 
on up to 7 ce. alkalinity a month later, indicating the com- 
plete absence of free COz. This condition remained for over 
a month, or until September 12, when the rains and cloudy 
days restored neutrality and reduced the amount of oxygen 
in solution, partly by the presence of decaying organic matter. 
From this time on to middle or late December the amount 
of oxygen decreased and the CO: increased, the alkalinity dis- 
appearing and the water showing a large amount of free car- 
bon-dioxide. This does not mean that these are mutual 
opposites acting like a mechanical couple. The increase in 
one is not always proportional to the decrease in the other, 
and vice versa, though in general that is true. There may be 
either an increase or a decrease in the amount of oxygen 
without any change in the alkalinity or amount of COs, and 
vice versa; but in general, the conditions which favor the 
increase of one cause a decrease in the other; in other words, 
it seems evident that the water is rendered neutral and later 
alkaline by the withdrawal first of free COz and then of the , 
half-bound COz from the bicarbonates by the rapid growth 
and active photosynthesis of plankton alg and shore aquatics 
which excrete an excess of oxygen. If the water is not 
disturbed by wind this may go on to supersaturation, which 
was really the case July 20 to 30, August 21 and Sep- 
tember 12. Saturation for that temperature, 27° C., accord- 
ing to the saturation tables of Roscoe and Lunt, is only 5.6 ec. 
per liter, while my figures for these dates show 7 cc., or 180%, 
of saturation. Thus while we should expect a decrease in 
both oxygen and carbon-dioxide with rise of temperature we 
find, instead, an increase of oxygen, due evidently to plant 
growth and activity, which diminishes the carbon-dioxide far 
below the saturation capacity or absorption coefficient. 
It will be further noticed that these fluctuations correlate 
