6 BULLETIN 960, U. S. DEPARTMENT OF AGRICULTURE. 
In this connection the source from which the water is drawn or the 
character of the soil in the reservoir is important. The water of a 
lake with a muck bottom and swampy margin has generally a lower 
oxygen content than one with a sand or gravel bottom. The studies 
of Birge and Juday (2) show that this applies to Wisconsin lakes and 
the studies of one of the writers (Bergman) have shown that the 
oxygen content of water from cedar-swamp reservoirs in Massachu- 
setts was only 10 to 40 per cent of that in clear pond water at the same 
time. For the same reason, the water of reservoirs constructed on 
marshes is usually low in oxygen content. 
The influence of light intensity on the oxygen content of flooding 
water and its relation to the water injury of submerged cranberry 
plants has been considered in another paper (1). Briefly, it may be 
stated that whereas the process of respiration, in which oxygen 
is taken up from the water by the submerged plant, goes on both in 
light and in darkness, the process of photosynthesis, in which oxygen 
is given off to the water by the plant, can take place only in the 
light. On a clear day the oxygen content of the water on a flooded 
cranberry marsh in growing condition increases. On the other 
hand, at night or in.cloudy weather the oxygen content of the water 
is reduced, and if the cloudiness persists for two or three days the 
oxygen content may become very low and injury may result. 
OXYGEN CONTENT OF WATERS USED IN FLOODING CRANBERRY 
MARSHES IN WISCONSIN. 
During September of the years 1918 and i919 determinations of 
the oxygen content of more than 130 samples of water from various 
marshes in Wisconsin were made. Winkler’s titrimetric method for 
determining the oxygen content of water (10, p. 2843) was used in 
all cases. 
From these analyses, of which Table If gives a few typical examples, — 
it is evident that’ the oxygen content of the flooding water of Wis- 
consin cranberry marshes is generally below saturation. In some 
cases the deficiency is very marked. This is due to the fact that in 
practically all cases the water is held in reservoirs constructed on 
marshes. 
These analyses show that the oxygen content of water in reservoirs 
and on the flooding sections of marshes increases during the day and 
that the increase is greater on clear days than on cloudy ones. This 
is illustrated by the analyses of reservoir water at Black River Falls. 
on September 10 and 11, 1919. On September 10, a cloudy day, the 
oxygen content of the water at the north end of the reservoir increased 
from 3.22 ¢. c. per liter at 11.30 a. m. to 3.74 ¢. c. per liter at 
4.45 p.m. On September 11, a clear day, the oxygen content of the 
