457 
of shoaler waters, from 50 to 20 em. Flag Lake also, in the shoal 
waters of the autumn of 1895, yielded a large production; and 
Thompson's Lake, in the low water of the autumn of 1897, gave 
the largest production on record for that season of the year in 
that body of water. The vernal pulses, noted for their large 
production, usually fall at the time of the run-off of large areas 
of slightly submerged bottom-lands. Shoalness, then, does not 
prevent large production. Indeed, there are some important 
reasons why shoal waters should, other things being equal, 
produce more plankton. Light pervades the water more com- 
pletely, aeration by wind and waves preserves the gaseous equi- 
librium more perfectly than in deeper waters, and upon sedi- 
mentation the suspended organic matters in the water are not 
removed from the immediate proximinity of the growing phy- 
toplankton. Their decay and solution renders them imme- 
diately available, while in deep waters only the slow process of 
diffusion, in the absence of vertical currents dependent upon 
temperature or hydrographic changes, brings them within the 
field of surface-dwelling plankton. 
It is well established that the plankton is relatively more 
abundant in the surface than in the deeper waters of the ocean. 
The researches of Reighard (94), Birge (95), and Ward (795) 
show conclusively that the surface waters of our larger lakes 
contain the greater part of the plankton. Thus, Reighard (’94) 
finds in Lake St. Clair from 1.2 to 37.2 times as much plankton 
in the surface stratum of 1.5 meters in depth as in the remain- 
ing bottom layer in depths of 2.2 to 8.4 meters. Birge (795) 
finds 50 per cent., or more, of the Crustacea of the plankton in 
the upper 8 to 4 meters, and over 90 per cent. in the upper 9 
meters in depths of 18 meters, and Ward (’95) reports 64 per 
cent. of the plankton in the upper 2 meters. 
Of our total 640 collections, 389 were made in water over 2 
meters in depth. In the Illinois there were 208 such out of 235; in 
Spoon River, 34 out of 35; in Quiver Lake, 60 out of 115; in Dog- 
fish Lake, 27 out of 48; in Flag Lake, 8 out of 44; in Thompson’s 
Lake, 48 out of 96; and in Phelps Lake, only 4 out of 67. Thus 
