336 
Mottier . — The Effect of 
direct connexion with nuclear division, while in Spirogyra 
and Mesocarpus both processes take place at the same time, 
although the transverse walls seem to be laid down in the 
same way in each plant ; that is, the membrane begins at the 
hautschicht and is developed inwards. The more intimate 
relation existing between the nuclei and these types of cell- 
wall formation, which may be designated as the Cladophora 
and Spirogyra types respectively, is virtually unknown not- 
withstanding the fact that both plants have become classical 
as objects of investigation. 
Gerasimoff (’9 7) has shown that, when dividing cells of 
Spirogyra and Zygnema are exposed to a temperature below 
o° C., the process of division is inhibited, and one of the 
daughter-nuclei may pass over into the other cell, thereby 
giving rise to an enucleated cell-chamber and one with two 
nuclei. He found also that similar results could be brought 
about by means of certain anaesthetics. 
A similar behaviour was observed in the course of my own 
studies upon Spirogyra. As previously stated, the plants 
were kept on ice over night, but the temperature never fell 
below o° C. As a rule, the temperature of the water contain- 
ing the plants when the vessels were removed from the 
refrigerator on the following morning was 3 0 or 5 0 C. 
In several cases observed, one of the nuclei moved back 
into the enucleated cell in four or five days after the experi- 
ment, but the ring-shaped transverse wall never developed 
further. Plasmic cords extended through the opening in the 
wall from one cell to the other. Other cases were noticed 
where both nuclei remained in the same cell-cavity, when one 
of them, and apparently that which had left its cell, became 
partly cut off from the rest of the cell by an irregularly- 
shaped membrane. For lack of time, a further study of this 
phase of the subject was impossible. 
As regards the type of cell-wall formation displayed in the 
vegetative division of cells of Cladophora , Spirogyra , Zygnema 
and Mesocarpus , it may be safely stated that, when the relation 
existing between a cell-wall in process of formation and the 
