254 BOTANICAL GAZETTE [APRIL 
case, at any rate, the importance of the plasma-membrane as a factor 
in such a cell-division should be emphasized. The process in Empu- 
sa, in fact, would seem to furnish an argument in favor of NOLL’s (:03) 
view that in Bryopsis the controlling factor of embryonic growth is 
located in the Hauischicht. Apparently in Empusa a definite region 
of the plasma-membrane is stimulated to action, a ring-formed infold- 
ing of the membrane occurs, and at once in the cleft thus produced, the 
new wall begins to be deposited. A darker accumulation, presum- 
ably of kinoplasm, may now be seen at the inner margin of the cleft 
(jigs. 18, 20), where the activities leading to the cleavage of the in- 
pushing plasma-membrane and to the ingrowth of the partition-wall 
‘are evidently greatest. But the plasma-membrane does not alone 
seem to be the active agent for these phenomena, for fig. 18 shows a 
darker portion, having appreciable thickness, which apparently marks 
a more or less broad region of concentration of kinoplasm. This fact, 
therefore, may be regarded as an argument against the plasma-mem- 
brane itself being the sole controlling factor in this case. Further, 
MortieR’s (’99) experiments on Spirogyra and Cladophora, in 
which, by reason of the disturbance due to centrifugal force, the cel- 
lulose-ring, when once begun, was never brought to completion, not- 
withstanding the fact that the plasma-membrane was still intact, fur- 
nishes very convincing evidence against the acceptance of the theory 
that the Hautschicht alone is the controlling factor of wall-formation 
in these instances. 
The fact that the cleft and ring-formed wall are finally carried 
across a wide vacuolar space (figs. 17-21), will not permit of the 
application to this case of SWINGLE’s (:03) explanation for the mechan- 
ism of the cleavage in Rhizopus, Phycomyces, and other forms. For it 
seems impossible to conceive how local contractions of the cytoplasm 
could cause the constriction of the cell in the case of Empusa. We 
could perhaps think of such a contraction as initiating the process, 
but that these forces could obtain after the narrow diaphragm of cyto- 
plasm had begun to be pushed across the central vacuole, seems to 
me inconceivable. 
In certain instances in Empusa, as, for example, when a germ- 
tube is formed (jigs. 8, g), the end cell of a filament keeps cutting 
itself off from behind, thus enabling the body of the protoplasm to 
