RA RN gg gy ce, 
1901] SPORANGIA AND GAMETOPHYTES OF SELAGINELLA 127 
Infrequently two mother cells occur, and these may go through 
all the later stages of development, thus forming eight spores in 
a megasporangium. Normally the membrane of the single 
mother cell becomes distended by the imbibition of fluid that 
has been poured into the sporangial cavity from the tapetum. 
Two successive divisions follow each other with great rapidity. 
The spindle of the first division I have seen but a few times; 
the two that follow, I saw more frequently (figs. 76, 177). 
These are extremely small and delicate, occupy the middle of 
the cell, and are soon much obscured by fibers which arise in 
the surrounding protoplasm. These fibers at first radiate in all 
directions from no definite center, but later assume the form of 
a sextuple spindle with the four daughter nuclei at the poles. 
No cytological work was attempted, beyond determining the 
method by which the spores originate, but it is evident even 
from a cursory examination that there is some connection 
between the enveloping spindle fibers and the two lumps lying 
against the nucleus which are represented in figs. rz, 13,75. In 
the meantime there has appeared a new membrane just within 
the mother cell wall (jig. 15). It is very delicate, but of 
unequal thickness, and can be detected only in particularly for- 
tunate sections. Whether this membrane arises by cleavage 
from the mother cell wall, or de novo from the protoplasm of the 
cell, is necessarily a matter of speculation in an object so small. 
Nuclear plates form across the spindles, and the mother cell 
divides into four spores tetrahedrally arranged. At the moment 
of their separation the nuclei lie near the bases of the spores, 
which correspond in position to the poles of the sextuple spindle, 
but soon move toward the apices ( figs. 16-18, 22). As the spores 
increase in volume, by their pressure outward, and by a folding 
inward on the part of the irregularly thickened special mother 
cell membrane above described, the tetrad presents the appear- 
ance of a four-lobed body surrounded by a single envelope whose 
continuity is not broken, floating in the fluid that fills the dis- 
tended spore mother cell membrane (figs. 17-19). Either the 
special mother cell membrane itself thickens, or a new Coat is 
