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influenced and defined to a considerable degree by the capillitial 
threads, just as in Physarella. 
As is well known, the sporangial wall in Stemonitis is very fragile 
and eventually disappears. In younger stages it may be noted as a 
thin bounding membrane; while from older or mature sporangia it is 
usually missing. In figure 21, from a preparation similar to the one 
from which figure 20 was drawn, this outer wall is shown, broken and 
removed from contact with the protoplasm. A very delicate, con- 
necting capillitial thread is to be seen in figure 21, its attachment to 
the sporangial wall qujte comparable to that already examined in 
Physarella. 
Figure 22 is a high power drawing of a mesh of the inner portion 
of the mature dried capillitium. As is indicated by the dotted line, a 
portion is clearly hollow; while other parts, due to their dark color and 
narrow diameter, did not present an appearance that could render 
possible a statement that they were hollow. Of course an appearance 
simulating hollowness can easily be obtained if a thread is slightly out 
of focus. There is, however, no doubt but that, though the lumen 
may be at times extremely capillary, the most of these threads are 
really hollow; a focus on a bent "knee" of an anastomosing thread, 
for example, often clearly demonstrates this point. 
General Discussion 
The term "vacuoles," as applying to the openings in which the 
capillitial threads are to develop, would seem to be misleading in the 
case of the two species under discussion, since these openings in ques- 
tion appear to be quite commonly, if not indeed invariably, invagina- 
tions from the sporangial surface, or from the plasma membrane 
bounding the columella. It is of course quite likely that these more 
or less tubular openings in the protoplasm are due to some tensions 
arising in the viscid mass; the fundamental causes resulting in this 
and related phenomena are, however, obscure. Much easier to under- 
stand, it seems to the writer, is the process of deposition of the fine, 
smooth capillitial threads. 
Taking first the case of Physarella mirabilis, tubular capillary 
spaces appear in early stages of sporangial development. These 
spaces are no doubt filled at their beginning with watery sap and 
aqueous waste, connected as they are with lime-knot spaces and 
opening upon the developing outer membrane. From the plasma 
