186 
ON THE PILOBOLIDJE. 
never seen it stated that the same regularity extends, in an 
appreciable degree, to sporangia containing, like those of 
Pilobolus, many hundreds of spores ; my observations have 
shown me that it is often so. 
/.—The Columella. 
While these changes are taking place in the sporange the 
perfectly plane septum which arose at first at the top of the 
stem, and the upper portion of the stem itself, have been 
undergoing transformations in form no less important. The 
upward tendency of the protoplasm, which must apparently 
be looked upon as a vital movement admitting of no further 
analysis, steadily continues and exerts a pressure upon the 
septum, which causes it to grow upwards in a bluntly conical 
form within the sporange (Fig. 10), and thus produce the 
columella so characteristic of the Mucorini. The columella, 
rising as it does among the spores, and displacing some of 
them, must cause a considerable pressure upon the wall of 
the sporangium, but, as the upper portion of this is already 
more or less cuticularised and capable of withstanding the 
strain, it follows that the whole effect must fall upon that 
infra-equatorial zone, before mentioned as exempt from 
the cuticularisation, which certainly is found to be, in the 
mature sporange, much thinner and more fragile than it was 
at first. 
It is curious to observe the difference between the 
behaviour of this septum, and of the one at the base of 
the stem. The lower one is pervious to the protoplasm, 
and remains always plane ; the upper one is impervious, and 
is consequently forced up as just described. 
< j . —The Swelling. 
The upper portion of the stem also yields to the pressure 
from within, and is swollen out into a more or less globular or 
ovoid form, characteristic of each species, which I shall call 
the swelling. At the base this swelling passes into the stem 
with more or less abruptness, and below this the stem 
remains, except in P. cedipns (Fig. 14), perfectly cylindrical 
down to the basal reservoir. The whole of the yellow 
granular substance is not absorbed in the formation of the 
sporange ; a small portion remains in the stem. The supply 
from the mycelium still continues, and the basal reservoir 
is often nearly full. That part which remains in the stem 
is distributed in a peculiar manner. When the swelling is 
already nearly completed, but the columella not yet elevated 
