412 BOTANICAL GAZETTE [JUNE 
seem to divide just as the entire cell divides in animals like the 
amoeba, but the constriction in these animals, it must be noted, 
is a constriction of the plasma membrane. In the present case 
it may be due to the constriction of a membrane forming the outer 
layer of the chromatophore, which may perhaps be regarded as 
similar to a thin tonoplast bounding a vacuole. Progressive cleav- 
age such as HARPER (21) has found in the sporangia of the fungi 
and slime molds, in which the mass of protoplasm is cut up by 
irregular cleavage furrows from the surface and from the interior, 
of course corresponds to the cell division and not to the division 
of the chromatophore in Closterium. The furrows in the sporangia 
are scattered throughout the cleaving mass, being perhaps due to an 
extrusion of water from its surface and interior, while in Closterium 
there is only one furrow, and this is localized in a definite zone at 
the middle of the cell. No nuclear changes are visible at this 
time, and any theories that connect nuclear division directly with 
cytoplasmic division, such as those of HemmENHAIN and KostTa- 
NECKI, would seem to break down in the present case. 
The nucleus, in the meantime, has apparently undergone no 
change that is visible externally (figs. 1, 9), the granular mass at 
the center being still present. The nucleus is in the process of 
spireme and chromosome formation during the time the chroma- 
tophore is dividing, although this process is not visible externally. 
Soon, however, some individuals (fig. 2) show the chromosomes in 
the equatorial plate stage on a cylindrical spindle whose ends are 
hidden by the projecting chromatophores. The nucleus now 
apparently disappears (fig. 3); the chromosomes, being drawn 
back to the ends of the spindle, are under the ends of the chroma- 
tophore and cannot be seen. Across the middle of the cell there 
is now (fig. 3) a very conspicuous broad band of granular matter, 
in the middle of which the new wall is put across. The two nuclei, 
having been reconstructed, can then be seen moving out to the 
surface of the chromatophore and making their way back (fig. 4), 
immediately under the plasma membrane, to the new position 
they are to occupy permanently in the new cell at the middle of 
each chromatophore. FiscHEer (14) states that these migrations 
