Igrt] LUTMAN—CLOSTERIUM AI5 
The nucleus in these two species seems to arrive regularly at 
the center of the new organism before the chromatophore has 
finished its division (figs. 5,6, 8,11). This confirms F1scHER’s (14) 
observation that the nucleus in C. moniliferum usually arrives at 
the constriction in the chromatophore before it is complete, and 
that the separation of the last strands is apparently finished under 
its direction. 
The resting nucleus 
_ As commonly figured in textbooks on the algae, such as OLT- 
MANN’S, the nucleus of Closterium is a lens-shaped or cylindrical 
body lying between the two halves of the chromatophore at the 
middle of the plant and containing a granular mass at its center. 
C. moniliferum is the species most frequently figured, and in it 
the drawings frequently show the two halves of the chromatophore 
Pulled back from each other, with the nucleus lying as a cylindrical 
structure, somewhat contracted at the middle, connecting them. 
I have already given a partial account (27) of the interesting 
and Suggestive structure of the resting nucleus, but in connection 
with the present work I have of course carefully examined again 
sreat numbers of nuclei, both in whole mounts and in sections. 
€ nucleus is very large for an alga, and presents almost as 
favorable an object for study as does that body in the majority 
of the flowering plants. There is quite a little difference in its 
Structure in the two species studied, although in a general way 
they are very similar, and are both essentially like that of Spirogyra. 
€ nucleus of C. Ehrenbergii is in the form of a biconvex lens 
figs. 14, 15), and I have never found it losing this shape as a result 
of the two halves of the chromatophore pulling away from each 
Other. In end view it is circular in outline, as shown in fig. 16. 
The mass of the nucleus is made up of a very fine reticulum 
Which stains very faintly both in the triple stain and in the iron- 
hematoxylin, and shows a few such chromatin granules as occur 
on the linin threads of many of the higher plants. If such granules 
“re present, they must be very minute or do not retain the stain. 
are darker staining places in the reticulum, but I should 
Mclined to regard these as net-knots rather than as definite 
*S. At the center of this fine reticulum is a mass of substarice 
