49 ° Harper «, — Cell-Division in Sporangia and AscL 
matter. The nuclei are certainly the centres about which the 
cleavage planes ultimately orient themselves, and it seems 
necessary to assume that some influence has passed outward 
from them and directed the whole process of the cleavage. 
Strasburger 1 , in connexion with Noll’s 2 doctrine that the 
protoplasmic membrane is the direct controlling organ in 
the growth of the coenocytic Algae, has pointed out that the 
nuclei may be the real controlling centres working through 
the protoplasmic membrane, even in resting cells, by means of 
impulses transmitted through the kinoplasm. My own observa- 
tions on spore-formation in the ascus point to the assumption 
that the plasma-membrane is itself kinoplasmic in its origin. 
If in Synchitrium the nuclei are centres for the formation of 
kinoplasm, and it proceeds outward from them by diffusion 
in all directions till it reaches the plasma-membrane, this will 
be correspondingly increased in thickness, and if the mass be 
decreasing in volume by loss of water and tending to split up 
like a mass of drying starch, the membrane might perhaps 
press into the furrows thus formed, so as to become the surface 
layer of the forming segments. The first furrows will show 
no specific orientation with reference to the nuclei, but as the 
process continues the nuclei forming the centres for building 
up and distributing this membrane-material will by reason of 
this very fact tend to occupy the centres of cleavage-segments, 
until ultimately each nucleus will have furnished sufficient 
material for enclosing itself in an independent membrane. 
The evidence in favour of the explanation of cleavage just 
suggested is by no means adequate ; still it will perhaps 
serve to bring out more sharply the elements of the problem 
to be solved. 
PlLOBOLUS. 
The method of spore-formation in the Zygomycetes is 
of especial interest, since we have here one of the most 
1 Uber die Wirkungssphare der Kerne und die Zellgrosse. Hist. Beitr. v, p. 981, 
1893. 
3 Die Wirkungsweise von Schwerkraft u. Licht auf die Gestaltung der Pflanze. 
Nat, Rundschau, Bd. iii, 1888. 
