CELL-DIVISION. 41 
nent part taken by the vacuoles in the former. Although the mem- 
branes of these vacuoles may not, at first, be exactly similar to plasma 
membranes, they are undoubtedly converted into them. Since we 
assume that the plasma membrane is largely of a kinoplasmic nature, 
and attribute to it something of a morphological rank in the cell, it 
may not be wholly fanciful to suggest that the limiting membrane of 
a vacuole may be developed into a real plasma membrane, and that 
this actually takes place in the plants in question. 
CELL-DIVISION IN DICTYOTA AND STYPOCAULON. 
There is yet another method of cell-formation which has been 
observed in certain of the brown alge that differs materially from the 
process of cleavage already described. There are no kinoplasmic 
connecting fibers by which a plasma membrane may be formed, nor 
is it a cleavage such as has been described for certain fungi. 
The plasma membrane, or cell-plate, seems to be formed directly 
out of the apparently undifferentiated framework of the cytoplasm. 
This type of cell-formation has been observed in such Pheophycee 
as Stypocaulon (Swingle, ’97), Mucus (Strasburger, ’97), and Dzc- 
tyota (Mottier, 1900). 
Swingle has followed the development of the cell-plate in great 
detail in the apical cell of Stypocaulon. Here each division of the 
nucleus is followed by a cell-division. The bulk of the cytoplasm 
presents a very beautiful and typical alveolar structure, and the first 
indication of a cell-plate is seen in certain alveole, which show a 
tendency to arrange themselves across the cell in a transverse plane 
(Fig. 16, B). As soon as this orientation of the alveolea becomes more 
marked, the transverse alveolar lamellz form a more continuous plane 
which, in section, appears as a very fine line. During these changes 
neither an increase in the number of connecting fibers between the 
nuclei nor any perceptible change whatever in the arrangement of the 
kinoplasm was to be seen. Only a few fibers or lines of force, indi- 
cated by the arrangement of the alveole of the frothy plasma, extend 
from the nucleus of the apical cell to the seat of cell-plate formation, 
and fewer still from the lower nucleus to the same place. It is certain 
that if there be real fibers, they must be extremely delicate and not 
numerous enough to lead one to suppose that the cell-plate is laid down 
by any such process as in the higher plants. 
The author has found that the development of the plasma membrane 
in the tetraspore mother-cell of Dictyota (Mottier, 1900) is similar to 
that of Stypocaulon. Here there is absolutely no visible trace of 
