496 
of vegetation on the distribution of the plankton. Only the quan- 
titative data are at present available, and the results are con- 
flicting. In some cases the plankton is greater in the vegeta- 
tion than in the adjacent open water; in others the reverse is 
true. These examinations were made at times of unstable 
river levels, and the movements of water consequent thereupon 
make any satisfactory analysis difficult. The general conclu- 
sion that lakes full of vegetation (Quiver) are everywhere 
poor in plankton, while those relatively free from it (Thomp- 
son’s and Matanzas) support generally a more abundant plank- 
ton is in all cases upheld by these examinations. 
This poverty of the plankton in vegetation-rich lakes was 
. one of the surprises of our investigations, and, so far as I have 
been able to ascertain, it contradicts the general expectation 
among observers of aquatic life. It has its parallel in the pau- 
city of life in tropical forests and among the pines and red- 
woods of the Sierras. It is fundamentally a problem of nutri- 
tion, and inheres in the utilization of the available food supply 
by a single type, or a few types, of plants which do not them- 
selves in turn afford support for an abundant or varied animal 
life. 
Wherever the depth of the water, the currents, the winds, 
or other factors, prevent the development of a submerged 
aquatic flora, the nutrient materials for plant growth—the oxy- 
gen, the carbon dioxid, the nitrates, phosphates, sulphates, and ~ 
carbonates dissolved in the water—are utilized by the phyto- 
plankton, which, in turn, supports the zodplankton. The en- 
tire production of such a lake takes the form of plankton and, 
in turn, of those larger species, insect larvee, mollusks, and fish, 
which are directly or indirectly supported by it. When, on the 
other hand, the conditions are such that a submerged non- 
rooted aquatic flora obtains possession of a lake,—as, for exam- 
ple, Ceratophyllum and Klodea in Quiver Lake,—these : nutrient 
- materials are appropriated by it to the great reduction, even 
practical exclusion, of the phytoplankton. In the struggle 
which must ensue between the phytoplankton and the sub- 
