498 H ar per .-Cell- Division in Sporangia and Asci. 
thickness and finally extends up the base of the columella. 
It is thickest at the angle which the columella makes with the 
sporangial wall and thins out toward the edges in both direc- 
tions. The substance of which it is composed is the same in 
appearance and staining reactions with the intersporal sub- 
stance (Fig. 24) which appears later, and which Brefeld has 
attempted to homologize with the epiplasm of an ascus. It 
is plainly to be seen here that this collar-substance is not 
protoplasmic, and is an excretion deposited outside the 
plasma-membrane bounding the spore-plasma. It is an 
excreted material, and designed for a special function in 
distributing the sporangia as Brefeld has pointed out ; but its 
perfectly homogeneous structure and its position outside the 
plasma-membrane of the spore-plasma prior to spore-forma- 
tion show that it is in no way comparable to the protoplasm 
left behind in the ascus in the process of free cell-formation as 
it takes place there. 
It is to be noted that the columella-wall has the same dome- 
shaped outline when it is first formed as it has later, when the. 
spores are ripe. It is not at first a flat transverse septum 
which is later pushed up into a dome as the spores ripen. 
Cleavage of the spore-plasma begins very shortly after the 
columella is complete. The protoplasm becomes somewhat 
vacuolar, and the nuclei are rather evenly distributed through 
its mass. Cleavage-furrows then appear around the base of 
the sporangium, cutting the surface of the protoplasm into 
irregular polygonal areas (Fig. 14). At the same time in the 
interior of the protoplasm, where hitherto only rounded or 
spherical vacuoles have been found, angular vacuoles, fre- 
quently three cornered in optical section, appear, and their 
edges cut outward through the protoplasm to meet similar 
cleavage-furrows from adjacent vacuoles (Fig. 14). The 
surface-furrows have also been growing deeper, and meet and 
become continuous with the edges of the vacuoles. The sur- 
faces of the vacuoles from being convex outwardly have become 
concave from the pressure of the adjacent plasma-masses, and 
the latter appear as intercellular spaces between the proto- 
