FOUR-LOB ED SPORE MOTHER CELLS IN CATHARINEA 459 
between the different plastids shown in figure 2, B-D, are at least in 
part due to the fact that these somewhat flattened bodies are seen 
from different angles. 
The fibers that appear in figure 2, A, running from each plastid 
toward the nucleus, seem to be the beginnings of a spindle which in 
its origin is quadripolar. The mature spindle is bipolar (figure 2, B). 
Each blunt pole lies between two plastids; the upper pole of the 
spindle shown in figure 2, B, is not directed toward a plastid, as the 
figure might suggest, but lies at a higher focus and between this plastid 
and another one, not present in the section from which the figure was 
drawn. Both the first (heterotypic) and the second (homoeotypic) 
nuclear divisions are followed by the formation of cell plates and of 
partition walls. Figure 2, C, shows the wall that divides the spore 
mother cell after the first nuclear division, as well as the beginning 
of the formation of a cell plate on one of the second division spindles. 
As this figure also shows, the spindles of the second division are so 
oriented that each spindle pole is directed toward, and in contact with, 
one of the four plastids. Consequently, each of the daughter nuclei 
resulting from this division lies in contact with a plastid (figure 2, D). 
The formation of partition walls after the second mitosis completes 
the division of the spore mother cell into four spores, each of which 
contains a nucleus and a plastid and corresponds substantially (except 
for the nucleus) to one of the lobes of the mother cell. 
After cell division has been completed, the original wall of the 
mother cell and the partition walls separating the spores gradually 
soften. The spores round up somewhat, and each forms an indepen- 
dent wall, at first quite thin, about itself and inside the softening 
substance of the older walls (figure 2, D). Finally the dissolution of 
the old walls reaches the stage at which the spores become free. 
This is, I think, the first observed case of the occurrence of four- 
lobed spore mother cells in a bryophyte not a member of the Junger- 
manniales. It remains to be seen to what extent this character appears 
among the Bryales. Such studies of sporogenesis as have been made 
in members of the latter order seem to indicate that in general the 
mother cells are not lobed. The taking on of a lobed form is of 
interest because it anticipates the division of the cell at a time when 
there is no evidence either of a preparation for division on the part of 
the nucleus or of the development of the spindle mechanism. Another 
anticipatory step is seen in the early division of a single plastid into 
