Harper .-Cell- Division in Sporangia and Asci. 497 
by flattening and lateral fusion of originally ellipsoidal or 
spherical vacuoles, that is, the cleavage is not entirely by 
a furrow from the plasma-membrane at the mouth of the 
sporangiophore, but is at least in part a process of separation 
by excretion of liquid into vacuoles and their fusion side by 
side in situ. These vacuoles are not situated on the extreme 
boundary of the protoplasm adjacent to the large central 
vacuole, but are placed where the dense spore-plasma first 
becomes characteristically spongy. At the base of the 
sporangium indeed they cut through plasma as dense as the 
densest spore-plasma of the sporangium. Why the cell-wall 
of the columella could not be deposited on the surface of the 
central vacuole as well as on the surface of the small vacuoles, 
and thus enclose all the protoplasm in the sporangium, is an 
interesting question. The necessity is evident that the 
cleavage should proceed through a tolerably dense plasma, 
and this is perhaps due to the need of two protoplasmic sur- 
faces in contact, in order to form a cell-wall. It would seem 
otherwise quite natural that the spore-plasma should simply 
bound itself off by a wall against the central vacuole of the 
columella, in which case only the plasma at the mouth of 
the sporangiophore would need to be cut through, and the 
cleavage process would be apparently simplified. 
The cleft separating the spore-plasma from that of the colu- 
mella is quite wide and irregular at first. Later, the turgor 
of the two separated plasmic masses causes them to be firmly 
pressed together. This whole process of the delimitation of 
the spore-plasma is accomplished without the formation of 
a cell-wall, and consists simply in the establishment of new 
protoplasmic membranes. The cell-wall is deposited later, in 
the cleft between the two membranes. 
With the cutting off of the columella, the so-called collar 
begins to form on the basal wall of the sporangium, just out- 
side the mouth of the sporangiophore. It appears first as 
a thin layer of homogeneous material which, with Flemming’s 
triple stain, becomes faintly blue in colour (Figs. 14 and 15). 
After the columella-wall is laid down it increases rapidly in 
