6 
497 
merged aquatic flora for the possession of a body of water 
capable of supporting either, the greater duration and perma- 
nence of the larger plants which constitute the submerged 
flora must in the long run inure to the advantage of the latter, 
hence they predominate over the phytoplankton wherever 
other conditions favor their appearance. This coarse sub- 
merged vegetation cannot in its living condition be utilized by 
the minute organisms of the zoéplankton, and only such as 
feed upon it in decay can find sustenance in the vegetation-rich 
lake. The absence of an abundant phytoplankton and of the 
greater part of the zodplankton may thus be accounted for in 
waters rich in submerged and non-rooted vegetation. The 
total production of such a body of water consists mainly of a 
large amount of coarse aquatic vegetation, which but few ani- 
mals can utilize in its living condition as food, and a much re- 
duced plankton, largely of animal constituents, together with 
such larger and often attached species as find food in these 
elements. 
Some light on the relation of vegetation and plankton to 
certain of the chemical constituents of the food of the aquatic 
flora can be gained from a comparison of Plates XLV., XLIX., 
and L., and Tables X., XII., and XIII., which show the results 
of analyses in 1895. The appended table also gives the average 
AVERAGE OF ALL ANALYSES—PARTS PER MILLION, 
Station Free Ammonia Nitrates 
2 ; | : 
June 1 to Octo-| Remainder \June 1 to Octo-| Remainder 
ber 1, 1808 of year ber 1, 1898 of year 
Thompson's Lake...... 154 -457 244 .684 
Mover Lakes nce. omen | .024 199 222 -923 
Illinois River........... -566 786 297 1.036 
amounts of free ammonia and nitrates in Illinois River and in 
Quiver and Thompson’s lakes in the period from June 1 to Oc- 
tober 1 and in the remainder of the year—two periods which 
approximately represent the times of maximum and minimum 
of chlorophy]l-bearing organisms. 
