CLEAVAGE IN DIDYMIUM MELANOSPERMUM (PERS.) MACBR. I35 
place along the surface of the capillitial threads as well as upon the 
external surface of the protoplasmic mass as a whole. These sap 
cavities on the capillitial threads become very abundant, extending 
throughout the whole peripheral region of the spore-plasm. They next 
become connected along the threads and we have thus as it were 
canals running radially in the peripheral region of the cytoplasm and 
filled with a watery extruded liquid. Figure 5 shows the apparent 
vacuoles somewhat ellipsoidal in form as they run together. This 
change in their form and their resulting confluence are no doubt due 
to the continued extrusion of water from the protoplasm in preparation 
for spore formation. These watery sheaths open to the exterior at 
the ends of the threads, forming, as noted, tubular canals about the 
capillitial threads leading down into the protoplasmic mass. The 
extruded cell sap now apparently flows out quite freely, leaving the 
spore-plasm once more quite dense, but it does not again come into 
close connection with the surfaces of the capillitial threads (figs. 6 
and 8). Such radial sections at this stage show thus what appear to 
be clefts running through the spore-plasm. That they are not furrows 
but are merely tubular depressions enclosing the capillitial threads is 
clearly shown in tangential sections of this same stage (fig. 10). 
The contraction of the protoplasm and extrusion of liquid occurs 
also in the region next the columella so that we have the same appear- 
ance of clefts here (figs. 6, 8), and as the contraction continues it 
is possible to trace these tubular openings about the capillitial threads 
from the periphery to the center as continuous openings through the 
protoplasm (fig. 9). The appearance of these radial clefts sharply 
differentiates this stage from the earlier conditions shown in figure 2. 
As noted, a tangential section at this stage (fig. 10) shows the proto- 
plasm pierced by rounded or angular openings in each of which the 
cross section of a capillitial thread is found. The angular openings 
represent the later stage and are formed from the rounded openings 
by the formation of cleavage furrows from their surface. These 
furrows cut into the spore-plasm and tend to divide it up into radially 
placed prisms or cylinders. Sometimes more than one capillitial 
thread will be found in a single opening. Very soon the furrows from 
adjacent openings come together making irregular branching series 
of clefts. More or less horizontal radial sections at the stage when 
the furrows first begin to form about the capillitial cavities are shown 
in figures 9 and 1 1 . We see in such sections that the end of each prism 
