358 
Mottier . — The Effect of 
down through the instrumentality of the connecting fibres. 
The peculiar cellulose-ring formed preparatory to cell-division 
in Oedogonium may be brought into the same category with 
Spirogyra and Cladophora , bearing perhaps a closer resem- 
blance to the type of the former. 
It is not easy to understand why in Cladophora the mem- 
brane once begun as a cellulose-ring is never brought to com- 
pletion after a displacement of the cell-contents, without 
assuming that some very close relation exists between the 
nuclei and the origin of the transverse membrane, and that 
this relation having been once disturbed is never re-established. 
Since centrifugation never plasmolyzed the cells in question, 
the ectoplasm or hautschicht remained always in contact 
with the cellulose-ring, so that no mechanical injury could 
arise from that source. There are therefore strong grounds 
for the conclusion that in the Cladophora and Spirogyra types 
of cell-division a close relation exists between the nucleus 
or nuclei and the forming transverse membrane, and that, 
when such relation is once disturbed through a displacement 
of the nuclei in the cell by centrifugal force, it is never fully 
restored and the protoplast is incapable of completing the 
membrane. 
It might be of interest in this connexion to know whether 
spiral or other secondary thickenings would develop further, 
if, at the beginning of the process, the contents of those cells 
were displaced in a similar manner. 
Again, such cases as that illustrated in Fig. 3 present 
phenomena for which the writer is, as yet, unable to find 
a satisfactory explanation. It would seem at first that the 
size of the resulting cells might be proportional to the 
quantity of cytoplasm, and that that factor is the determining 
principle. Cell a , Fig. 3, contains more chlorophyll and 
probably a greater number of nuclei than cell h, but whether 
the quantity of living substance apart from nuclei and 
chloroplasts is proportional to the sizes of the respective 
cells I am unable to say. It is more probable that the 
position of the division-wall is determined here also by 
