154 
BULLETIN OF THE BUREAU OF FISHERIES 
the volume of plankton after August 18 remains higher than it was before July 25. 
In the discussion of the free C0 2 (p. 145) it has already been pointed out 
that the enormous increase in the volume of net plankton during the latter part of 
July and the early part of August was due to the production in large numbers of 
the flagellates — Pleodorina and Pandorina. It has also been mentioned (p. 145) 
that the rise in the phytoplankton is associated with a high phenolphthalein alka- 
linity; namely, 68.76 p. p. m. at 8 a. m. on July 30 and of 72.80 p. p. m. at 3 p. m. 
on August 9. In discussing the dissolved oxygen it has been mentioned that the 
maximum of 12.21 p. p. m. occurred on July 30; that is, during the period when 
the net plankton ran high. Plankton counts show that on July 29 a liter of water 
contained 960,000 colonies of Pleodorina and on July 30, 115,200 colonies of Pleodo- 
rina and 756,000 colonies of Pandorina. (Table 8.) (The figures for the net plankton 
in this pond along with those for the phenolphthalein alkalinity and the dissolved 
oxygen give some idea as to the magnitude of the changes that may take place when 
everything is favorable for photosynthesis.) The average amount of net plankton 
for 68 samples was 1.22 cubic centimeters per 10 liters of water. 
Table 6 shows that the behavior of the net plankton in C 2 was less striking 
than was the case in C 1 . As the tables show the variation here was from 0.10 to 1.0 
cubic centimeters per 10 liters of water, the total amount of net plankton produced in 
this pond is far less than that in C 1 . The average for 68 samples from C 2 was 0.43 
cubic centimeter; the average for an equal number of samples from C 1 was 1.22. 
This is a ratio of very nearly 1 : 2.3. This apparently contradicts the fact that the 
net loss on ignition in C 2 was slightly more than three times as large as that in C 1 . 
However, it serves to emphasize the fact, already referred to in the introduction, 
that the volume of net plankton is not always an absolute standard whereby the 
productivity can be measured. This is well illustrated by the fact that even in C 1 
the maximum for the net plankton does not correspond to the maximum for the 
loss on ignition. Again, on July 30, when the net plankton in C 1 and C 2 amounted 
to 3.5 and 0.48 cubic centimeters per 10 liters of water, respectively, the loss on 
ignition in C 1 was 3.69 milligrams per liter, and in C 2 it was 27.99 milligrams per 
liter of water. Plankton counts made on the centrifuge plankton of that date show 
that in C 1 each liter of water contained 115,200 colonies of Pleodorina and 756,600 
colonies of Pandorina and that each liter of water in C 2 contained 40,200,000 fila- 
ments of Aphanizomenon and 4S0,000 filaments of Anabaena. The reason why the 
loss on ignition and the volume of net plankton do not always agree is due to the 
fact that the centrifuge removes small organisms and fine detritus that would pass 
through the net. 
In pond C 3 the volume of net plankton varies from a minimum of 0.10 cubic 
centimeter per 10 liters of water to a maximum of 0.92 cubic centimeter per 10 liters 
of water. The average for 68 determinations was 0.36 cubic centimeter. The average 
amounts of net plankton for C 3 and C 2 do not differ very much. As Table 6 shows, 
there are brief intervals when the production in C 3 exceeds that in C 2, but on the 
average C 2 keeps somewhat ahead of C 3. 
In control pond C 4 the volume of net plankton from 10 liters of water ranged 
from a minimum of 0.03 cubic centimeter to a maximum of 0.40 cubic centimeter. 
The average for 68 determinations was 0.12 cubic centimeter. This is exactly a 
third of the average for C 3, a little better than one-fourth the average for C 2 and 
approximately a tenth of the average for C 1 . The same thing, therefore, that holds 
