200 
BULLETIN OP THE BUKEAU OF FISHERIES 
these data on the basis of Table 8, is 21.3, which is to be compared with 19.6 per cent 
in Table 8, derived from other data, and with 21.9 per cent in Table 10, resulting 
from a computation that includes the fats. The differences are plainly very small. 
Table 10 shows the percentile composition of the organic matter in the more 
important items of Table 9. The figures for Lake Mendota may be compared with 
those for the plankton of that lake, as reported in the plankton report on page 196. 
There the average of 87 specimens gave protein, 44.5 per cent; fat, 7.5 per cent; 
carbohydrate, 48 per cent. These figures show clearly the relative decrease in the 
proteins and fats of the dissolved matter as compared with those of the plankton, 
and the corresponding relative increase of the carbohydrates. 
If the total organic matter is computed from the data in Table 9 on the basis 
employed in Table 8, the excess due to computing all nonnitrogenous matter as 
carbohydrate ranges from 0.19 milligram in the case of Green Lake to 0.55 milligram in 
the bottom water of Mendota on June 25, 1924. The per cent of excess ranges from 2.2 
to 3.9; the average excess in the 8 cases is 0.35 milligram per liter, and the average 
per cent is 3.0. This correction might be applied to the figures of Table 8, if desired, 
but the error due to method of computation doubtless is much smaller than those 
inherent in the variations due to sampling. 
Table 11 exhibits the general results for Lake Mendota. The data for the 
plankton are the mean of 87 analyses of plankton taken from April 1 , 1915, to June, 
1917; the data for dissolved matter are from 20 residues, taken from 1922 to 1924 
So far as the total amounts are concerned, the result would have been virtually the 
same if the figures from Table 8 had been used instead of those from Table 9. Further 
study certainly will make changes in the figures here reported but is not likely to 
alter the general situation shown by them. 
Table 11.— Lake Mendota. General result 
Plankton 
Dissolved 
Total 
Milli- 
Milli- 
Milli- 
grams 
Per cent 
grams 
Per cent 
grams 
Per cent 
per liter 
per liter 
per liter 
Crude protein 
0.88 
44.5 
2.76 
21.9 
3. 64 
25.0 
.15 
7.5 
.56 
4.4 
.71 
4.8 
Carbohydrate - 
.95 
48.0 
9.27 
73.7 
10.22 
70.2 
Total 
1.98 
100.0 
12.59 
100.0 
14.57 
100.0 
Thus, the water of Lake Mendota contains an average of nearly 15 milligrams of 
organic matter per liter; less than one-seventh of this is contained in the plankton 
that may be collected with the net or extracted with the centrifuge. The maximum 
amount of organic matter yielded by the plankton when it was a special study was 
3.33 milligrams per liter on April 15, 1916; this is less than 40 per cent of the minimum 
amount of dissolved matter reported in Table 8. The minimum amount of plankton 
was taken on March 9, 1917, and yielded 0.91 milligram per liter. This is larger 
than several of the plankton catches reported in Table 8, but these were taken at 
one level only while the plankton catches for the plankton report represent all depths 
of the lake taken meter by meter. The water from which the dry residues came also 
