145 
evidence on this point; but to come to conclusions it is only necessary 
to assume that chlorophyl-bearing organisms presently arrive in the river 
whenever conditions appear favorable to their maintenance and multipli- 
cation, an assumption warranted by all our studies, and those of others, 
upon the river and elsewhere and at other times. Such conditions 
occurred in their earlier phases between Lockport and Morris before 1900 
at low water; but in 1911 not until somewhere between Marseilles and 
Spring Valley; while optimum conditions for green plankton apparently 
occurred at or above LaSalle before 1900, but in 1911 not much if any 
above Chillicothe, and in 1918 not much above Peoria. 
More recent evidence of a still continued gradual creeping down- 
stream of pollutional conditions is found by comparison of collections 
made in 1911 with those obtained in August, 1918. In the former year 
a foul-water fungus (Sphaerotilus natans) disappeared from both channel 
and shore at or near Starved Rock, while August 28 to 30, 1918, it was 
found in the river at Henry, 35 miles below Starved Rock, and also at 
Lacon, 6 miles still farther down. At Henry, it was quite healthy, with 
normal cell-division in progress. 
Other evident indications are given by collections of two Lake 
Michigan diatoms (Tabellaria flocculosa and T. fenestrata), which come 
into the river through the sanitary canal. In 1910 these clean-water plants 
managed to survive in small numbers, as they passed down-stream, but 
were always of a pallid, sickly color until they reached Chillicothe, and 
here the water was clean enough to permit their return to normal condi- 
tion and to a rapid rate of multiplication; while in August, 1918, their 
numbers declined steadily down-stream, until at Pekin they disappeared 
almost completely. ; 
Another Lake Michigan diatom (Melosira granulata var. spinosa) 
which lived through the worst pollution of 1910 and began to multiply at 
Spring Valley, does not now do so until it passes Chillicothe, 36 miles 
farther down. 
13. Consistenly with the foregoing statements, the ratios of total 
nitrogen, whether expressed by parts per million or as kilograms per 
second, now escaping into the Mississippi River are larger than they 
were in 1899. The nitrogen ratio at Grafton in 1899 was to that of 1914 
as 1 to 1.60 in the spring months (April to June), and as 1 to 1.26 in the 
summer months (July and August) ; and in kilograms per second these 
ratios in 1899 were to those of 1914 as 1 to 3.46 in spring and as 1 to 
4.83 in summer: In other words, between 1899 and 1914 the total nitrogen 
im a given quantity of the river water was increased by about one-fourth 
in spring and by six-tenths in summer, while the total for the entire flow 
of the stream in a given time was, in spring, 3% times as great in 1914 as 
in 1899, and in summer about 4.8 times as great. The nitrates, on the 
other hand, at the mouth of the river were, in parts per million, as 1 in 
1899 to 1.48 in 1914. It would seem from this that the nitrogen-consuming 
organisms have not increased in quantity since 1899 as fast as their food 
supplies. 
