164 BOTANICAL GAZETTE | SEPTEMBER 
there is no change of a middle layer in the cell plate into a cel 
wall. This conclusion rests mainly upon the fact that the halves 
of the cell plate which appear after splitting are together equa 
in thickness to the original plate, 7. ¢., there has been no diminw- 
tion of the substance of the cell plate during the process of 
splitting. That the cell wall is not a differentiated portion of 
the cell plate seems to me to be further shown by those cases it 
which portions of the separate halves of the cell plate appeat 
with no cell wall between them (figs. 30, 37). | 
The splitting seems to be due primarily to a differentiation 
of the substance of the plate itself into two layers. Of whit 
this differentiation consists is by no means apparent. It is hard 
to conceive of a layer of protoplasm becoming differentiated 
into two separate layers similar in all apparent respects to each 
other. To be sure, the two layers form the boundaries of sia 
rate cells, a fact which may be taken to indicate a possi . 
chemical difference between them. This differentiation, iM itself 
moreover, would not account for the separation of the halves of 
the plate. A possible explanation for this latter phenometo® 
may be that there is secreted between the halves some non-stall® 
able substance, perhaps cell sap, which serves to separate thee 
The apparent disappearance of the carbohydrate material befor 
the cell plate halves appear separated may mean that there 
change in this substance, preparatory to its being deposited # 
wall, of such a character that it does not take the same ee 
before. It may be that it simply forms a less dense eee . 
and that in this form it is first deposited between the halves 
the cell plate. The appearance of a stained wall would take 
mean that the substance had again become dense enough eed | 
the stain. While the above explanations are purely hypothe! . 
I cannot see that they in any manner do violence to the 
facts. They are suggested only in order to help bring oe 
connection that the splitting of the cell plate is apparen” : 
quite analogous to the longitudinal splitting of tae is : 
thread, unless Strasburger’s view that the granules div! = : 
