54 
AMERICAN JOURNAL OF BOTANY 
[Vol. 
almost no injury was evident. In the set of tubs in Spectacle Pond the 
same thing occurred. The plants in the shaded tub were obviously seriously 
injured while the vines in the Unshaded tub escaped with little or no ap- 
parent injury. It will be observed on consulting the graphs that the oxygen 
content of the water in the shaded tubs both in Spectacle Pond and in the 
II 
I 
Si 
1 
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POA/D 
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N 
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1 
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Fig. I . Oxygen content of water from Spectacle Pond and the State Bog ditch, East 
Wareham, Massachusetts, 1919. 
ditch dropped very rapidly after the experiment was begun and remained 
at a very low and essentially constant level throughout the course of the 
experiment. That the oxygen content did not reach a point of absolute 
deficiency at any time is probably to be accounted for by the fact that oxygen 
is taken up slowly from the air. 
The oxygen content of the unshaded tubs, both in Spectacle Pond and 
in the ditch, showed considerable variation between the day and night 
periods (figs. 2 and 3). The variation between day and night was very 
uniform throughout the experiment, the oxygen content of water in the 
unshaded tub in Spectacle Pond running slightly higher than in the unshaded 
tub in the ditch. The oxygen content of the water in Spectacle Pond showed 
very little variation from day to day or between day and night (figs, i and 
2) at any time during the experiment. Only on two occasions was a con- 
siderable change in the oxygen content of the pond water observed. One 
of these was at five o'clock on the morning of June 30, the other at nine 
o'clock on July 2. The decrease in the oxygen content of the water at these 
times is due to the fact that the water samples were taken too close to the 
outlet ditch from the State Bog, so that the sample contained a considerable 
portion of bog water mixed with the pond water. As the bog water contains 
considerably less oxygen, the result of mixing it with the pond water is to 
reduce the oxygen content of the latter. 
The ditch water also showed a wide variation between day and night in 
