1022 The American Naturalist. [December, 
thus appears that the heavy growths of the Diatomacex are 
somewhat more likely to be found in the deep than in the 
shallow ponds. The same may be said of the Chlorophycee, 
though the difference is not so marked. 31 per cent of the 
deep ponds and 27 percent of the shallow ponds at times 
have growths as high as 1000 per c.c. The Cyanophyce and 
Infusoria, on the other hand, incline towards shallower water. 
In the case of the former, 18 per cent of the deep ponds and 
34 per cent of the shallow ponds at times have growths of 1000 
per c.c., while in the case of the latter the figures are 12 per 
cent and 32 per cent respectively. 
In this connection it would be of interest to show statistically 
the relation that undoubtedly exists between the growths of 
organisms and the character of the material forming the bot- 
toms of the ponds, but unfortunately the necessary data is 
lacking in too many cases. So far as observations have been 
made, however, it appears that muddy bottoms are very largely 
responsible for "p excessive growth of microscopical organ- 
isms. 
An important question, and one which is of particular in- 
terest to water analysts, is the relation between the growths of 
organisms and the chemical analysis of the water in which the 
organisms are found. Unquestionably there is such a relation, 
and we should very much like to be able to take up a chemi- 
cal analy sis and say “ this water contains such and such sub- 
stances in solution, and, therefore, such and such organisms 
may be expected to ihirivë well in it.” In other words, we. 
desire to know better the nature of the necessary food oe 
of the microscopical organisms. 
The following tables are designed to show in a very oneta 
way the relation between the organisms in our 57 selected 
ponds and some of the important elements of the chemical 
analysis. These bring out several important facts. 
First, it is seen, that the color of a water has an important, 
influence upon the number of organisms that. will be. found. 
therein. Of the 24 cases where the Diatomaceæ are commonly 
found higher than 1000 per c. c., 12 (or. 50 per cent) occur, in, 
light colored waters, i, è. Water having a color lower than 0, 30 
