tort] LUTMAN—CLOSTERIUM 409 
very peculiar structure of the nucleolus as I have previously 
described it (2'7). If the chromosomes fuse together in the telo- 
phase of the divisions of the Conjugatae to form a large central 
body or bodies, this ought to be a favorable place to find them, 
for this mass is certainly a composite one. 
This work was begun at the University of Wisconsin under the 
direction of Professor R. A. HARPER, but was completed after leav- 
ing his laboratory. I am since greatly indebted to him, however, 
for his critical reading of the manuscript of this paper and for his 
suggested changes. 
Methods 
I have already described in my previous paper (27) my method 
for fixing, imbedding, and sectioning Closterium, and will only refer 
briefly to it here. As had happened in the two preceding years, 
the lily tanks in the botanical greenhouse at the University of 
Wisconsin were rapidly becoming covered with Closterium on the 
bottom and sides in the early part of May 1909, the organisms 
occurring in such abundance that they could be obtained in quantity 
and under favorable conditions for the study of their asexual 
reproduction. They have regularly disappeared from the tanks 
during the winter, whether due to the water becoming cold or from 
their going into the resting condition could not be determined, 
but they have just as regularly begun to appear again in quantity 
about the middle of April. The first series of fixations was made 
the night of May 2, beginning at 11 p.m. and continuing hourly 
from that time until 5 A.M. Four other series were fixed during 
the month of May. It was found that the early stages of chromato- 
Phore and nuclear division occurred more frequently early in the 
evening, even as early as 9 P.M., so the major part of my work 
has been done on material obtained from that time until mid- 
night. The time of the maximum number of divisions is undoubt- 
edly dependent on the character of the preceding day, whether 
cloudy or bright, determining the amount of starch stored, and more 
especially on the temperature of the water, although no accurate 
observations were made on these factors. 
The physiological condition of the individual plants also deter- 
_ Mines their ability to divide, the particular condition required 
