506 
in the river than in Phelps Lake. A further inspection of the 
table indicates that Phelps and Thompson’s lakes and Spoon 
River exhibit the most stable relations in productive rank. 
It is in these bodies of water that we have found environment- 
al conditions most uniform. In Flag, Quiver, and Dogfish 
lakes the divergences in rank are much greater, and it is in 
these localities that conditions of high and low water and of 
vegetation afford sharpest contrasts. In the [linois River 
itself, where hydrographic fluctuations are most immediately 
effective, we find apparently the widest divergences in produc- 
tive rank. Even in these instances of greatest divergence the 
tendency towards a certain rank in production in each locality 
is sufficiently evident to warrant the statement that in the 
main the relative rank in production in the several localities 
examined by us is well established and generally maintained. 
Still more pertinent to the question of the existence of a 
normal regimen in production is the question of sequence in 
the course of production in successive years and in different 
localities in the same year. Do the planktographs form curves 
which may be superposed in successive years in the same lo- 
cality or in different localities in the same year? A single 
glance at the plates which accompany this paper will suffice 
to reveal the chaotic complex of lines which such a superposi- 
tion would produce. There is no such unity or similarity if 
we base the comparisons on the actual volumetric production. 
If, on the other hand, we disregard coincidence in amplitude of 
the curve and consider mainly the direction of the changes, sim- 
ilarity becomes increasingly apparent. It rarely approaches 
to the condition of complete parallelism, however, owing to 
the great variety in the amplitude of production in various 
years and localities. 
If the data in the table following page 342 be analyzed with 
reference simply to the upward or downward movement in 
mean production from month to month and year to year in the 
various localities, we find certain tendencies appearing which 
may afford a basis for predicting the probable course of pro- 
