188 BOTANICAL GAZETTE [FEBRUARY 
made in 1916 by HeEartH shows the total solids in the main lake 
to be 13,020, or about 1.3 per cent; in Minnewaukon Bay above 
the grade, 0.4464 per cent; Court Lake, 0.12 per cent; and Lake I, 
0.1328 per cent. The water in all of these lakes shows the same 
large amount of magnesium sulphate. 
These conditions of salinity are correlated with seen differ- 
ences in the diatoms. The portion of Minnewaukon Bay from 
which the sample was taken was formerly part of the main lake 
and its water had about the same degree of salinity. But within 
the past year a highway grade has been made, cutting it off, and it 
is now connected with the main lake only by a culvert. Through 
this culvert the main lake receives about 2,000,000 gallons of water 
daily. This leaves the water in the bay practically fresh. In a 
collection made in this bay 14 species of diatoms were found, all 
but one of which are also found in the main lake. This one species, 
Stephanodiscus niagrae, is a fresh-water species. In this case a 
change in the condition of the water of from 1.3 per cent to 0.4464 
per cent of solids has in one season made practically no change in 
the diatoms. 
Lake I contains 0.1328 per cent of solids, or about one-third 
as much as Minnewaukon Bay. Instead.of having been separated 
from the main lake only a few months, as in the case of Minne- 
waukon Bay, it has been separated for about 5 years. In this lake 
24 species were found, 6 of which are not found in the main lake. 
These 6 are all fresh-water species. 
Court Lake contains 0.12 per cent of solids, nearly the same as 
Lake I, but of the 22 species of diatoms found in it, 13 are not found 
in the main lake, and all of these 13 are fresh-water species; but 
Court Lake has been separated from the main lake for about 100 
years. Since the main lake became salt, Court Lake has not been 
connected with it. These 13 species not found in the main lake, 
therefore, may have been originally in it and have died out on 
account of the saltness of the water; or they may have been intro- 
duced into Court Lake after the separation; or, what is more likely, 
some may have been in the original lake and others have been 
introduced later. 
The fact that little change has been made in the diatoms by the 
change of water in the branch of Minnewaukon Bay would indi- 
