490 THE AMERICAN NATURALIST. (VoL. XXXIII. 
brown water, with a depth of about twenty-five feet. From 
May 7 to June 7 the surface samples contained a few Mallo- 
monas. On June 14 there were 110 per cc., after which there 
were less than 11 per cc., until August 23 they suddenly rose 
to 2186 per cc. This suggested that there had been a growth 
at the top of the stagnation layer as in Lake Cochituate, and 
that a high wind had stirred the water and brought the organ- 
isms to the surface. This seemed the more probable, because 
the color of the surface water, which had been 0.57, rose to 
0.66. On August 27, four days later, samples were taken every 
five feet from surface to bottom. The following results were 
obtained. 
NuMBER OF 
DEPTH. MALLOMONAS PER CC. CoLor. 
1 ft. 20 0.54 
$ tt. 880 0.54 
10 ft.” 1936 0.57 
15 ft. 84 0.64 
20 ft. 40 1.06 
These observations seemed to show that there had been a 
large growth below the thermocline, that the organisms had 
been scattered through the water, and that they were now sink- 
ing back toward their original position. The color readings 
showed that the pond had been stirred to a depth of only about 
fifteen feet. 
On September 14 the vertical distribution was as follows. 
DEPTH. NUMBER OF MALLOMONAS PER CC. 
1 ft. o 
5 ft. ° 
15 ft. 10 
20 ft. 432 
25 ft. 472 
In November, during the period of autumnal circulation, 
Mallomonas again appeared at the surface, the number per cc. 
reaching forty. 
This tendency of Mallomonas to concentrate just below the 
thermocline was observed in Ridgewood Reservoir, Brooklyn, 
N. Y. In July, 1898, on the 6th inst., the water at the surface 
contained 60 per cc., while at the bottom (twenty feet) there 
