494 Harper .-Cell- Division in Sporangia and Asci. 
reaching a height of one to several millimetres the tip becomes 
rounded and swells rapidly to form the young sporangium 
(Fig. 9). No especial aggregation of the nuclei at the apex 
is to be noted at any time during this growth. They are 
rather evenly distributed throughout the sporangiophore-tube, 
and are present also in the hyaline plasma at the very tip. 
The growth is largely apical, rather than by stretching and 
deposition of new layers of cellulose on the inner surface of 
the stalk already formed. Well-fixed specimens show the 
paths of the streaming protoplasm in the sporangiophore 
very distinctly ; each streaming thread is seen to have marked 
a path for itself through the protoplasmic structure. It is 
bounded by continuous delicate films, quite distinct from the 
spongy structure of the adjacent plasma. Whether these 
streams flow upward only cannot be determined from fixed 
material. That these delicate threads are really the paths 
of streaming plasma-currents is evident from the further fact 
that after the sporangium is full grown and the columella 
has been formed, all trace of the threads disappears from the 
protoplasm of the sporangiophore. The paths of the proto- 
plasmic streams in the young sporangium are very well 
shown in sections such as are given in Figs. 10, 11. 
As the currents passing up in the stalk reach the enlarge- 
ment of the sporangium the streams seem to widen and 
thicken, indicating a checked velocity in the suddenly 
enlarged channel. This gives us the thickened ridge about 
the upper edge of the stalk shown in Fig. 2. From the upper 
edge of this ridge the currents spread into what in section 
is seen to be a fan-shaped series, distributing themselves to 
the surface of the sporangium from its apex through about 90°, 
thus building up the thickened layer which is to constitute 
the spore-plasma. In the lower half of the sporangium there 
is indicated a slight backward flow toward the mouth of the 
sporangiophore, thus filling the space gradually around the 
ridge which is built up around the mouth of the sporangio- 
phore. The whole process of the growth of the sporangio- 
phore and the inflow of protoplasm into the young sporangium 
