235 
sewage or the products of animal metabolism, such as might 
occur with the abundant plankton of that autumn (PI. XII.). 
The analysis of 1898 was made toward the close of a con- 
siderable rise, and it shows the effects of dilution of sewage in 
the lessened sodium chloride. The analysis of 1900 was 
made in a high-water period, and exhibits even a greater dilu- 
tion of sewage, as shown in the chlorine and ammonia salts. 
These analyses indicate an abundance of all the salts upon 
which plant life depends for its growth, and complete the 
demonstration of a chemical basis for the development in 
abundant phytoplankton. 
COMPARISONS WITH OTHER STREAMS. 
So far as I am aware this is the only instance in which 
opportunity has been offered for a comparison of the chemical 
conditions in stream waters and the plankton fluctuations coin- 
cident with them. Steuer (’01), who worked upon the plank- 
ton of the Danube, near Vienna, in 1898-99, cites averages of 
chemical analyses made in 1878. These analyses indicate that 
the Danube at that time was barren in comparison with the 
Illinois River. The average organic matter in solution as 
shown by the oxygen consumed was only 5.6 parts per million 
in the Danube to 43.4 (in 1898) in the Illinois River, while the 
chlorine was but 2.4 to 12.40. The conditions of analysis differ, 
so that the nitrogen content of the two streams cannot be 
compared, though the indications are that the nitrogen com- 
pounds are low in the Danube as compared with the Illinois 
River. The silica and carbonates are also lower in the former 
than in the latter stream. The poverty of the plankton of the 
Danube which Steuer describes, seems thus to be correlated 
with a deficient food supply, and the rich plankton of the Illi- 
nois with a more abundant one. 
In general terms, a chemical analysis of stream and lake 
waters throws some light on the productive capacity of the 
water. This appears in a comparison of the chemical condi- 
tions and plankton production of Quiver and Thompson’s lakes. 
