Centrifugal Force tip on the Cell. 335 
of the chlorophyll-bands was brought about, which consisted 
in a mere bending away of the displaced parts from the cell- 
wall. Under such circumstances recovery took place in one 
night. A redistribution of transversely displaced contents is 
accomplished in a relatively short time, especially in slender 
cells with few chlorophyll-bands which have not suffered 
appreciable injury. 
As in Cladophora , the most interesting phase of the sub- 
ject presented itself in the behaviour of those cells undergoing 
division at the time of the experiment. Material exhibiting 
dividing cells was obtained by placing the vessels containing 
fresh growing specimens on ice over night, and removing 
them the following morning to the temperature of the room 
(about 20 0 C.j. During a larger part of the day dividing cells 
may be found without difficulty in material thus treated. 
In dividing cells, the contents of one were forced through 
the circular opening in the transverse wall in process of 
formation provided that this opening was not less than one 
third or two-fifths the diameter of the cell. An end of 
a chlorophyll-band not infrequently caught against the edge 
of the partly formed membrane, when that end or portion 
remained in the otherwise perfectly colourless daughter-cell. 
In any case the bands on redistributing themselves began to 
creep back through the opening into the colourless cell. In 
Spirogyra, however, the redistribution of the cell-contents 
was never effected so regularly when a partly formed cell- 
wall interposed, and it could not be determined definitely 
whether the displaced daughter-nucleus returned to its cell. 
In Mesocarpus , where distribution is easier on account of the 
single straight chlorophyll-band, it was seen that the nucleus 
passed back with the chlorophyll-band into the colourless 
cell. In all such cases, division had not progressed far 
enough to sever the chloroplast. As in Cladophora , neither 
in Spirogyra nor in Mesocarpus was the transverse wall ever 
completed after its original connexion with the nuclei had 
been disturbed. 
So far as known, cell-division in Cladophora stands in no 
