Sty ke 2 cog Pa 
Igto} CHAMBERLAIN—DIOON EDULE 421 
should divide at every simultaneous mitosis. A rough estimate, 
based upon fig. 6, shows that the evanescent walls, to be described 
later, are those resulting from the tenth mitosis; and fig. 7, in 
which permanent walls have been established, ‘ecu that in this 
proembryo the permanent walls appeared in connection with the 
tenth mitosis. We have not found any case which would indicate 
an eleventh mitosis, and only a few cases where permanent walls 
seem to have been formed at the ninth mitosis; while nearly all 
proembryos in approximately the stage shown in fig. 7 indicate 
that there have been ten mitoses with permanent walls beginning 
in connection with the tenth. 
During the period of free nuclear division, the figures are entirely 
intranuclear and are characterized by the abundance and per- 
sistence of the spindle fibers (figs. 2-4). The nuclear membrane 
is formed quite late (fig. 3), but when once formed it becomes 
unusually thick, and pieces of it may be seen until late prophase or 
early metaphase of the next mitosis (fig. 2, 2). 
DIOON; EVANESCENT SEGMENTATION 
“The most characteristic feature of the proembryo of Dioon edule 
is the complete but evanescent segmentation of the entire egg. In 
one case, as early as the 64-nucleate stage, faint walls were observed 
dividing the entire proembryo into uninucleate cells. Such walls 
break down completely before the next mitosis begins. At the 
seventh and eighth mitoses, giving rise to the 128 and 256-nucleate 
Stages, the appearance of walls is more frequent and they break 
down less rapidly; while at the ninth mitosis, giving rise to the 
512-nucleate stage, the walls are probably always formed; and 
at the tenth division the walls are formed; but while they dis- 
appear in the upper portion of the proembryo, leaving it in free 
nuclear condition, they persist at the base, constituting the first 
permanent walls. As soon as the proembryo becomes cellular, 
€ simultaneous mitoses are succeeded by the scattered mitoses 
Which one expects in a young cellular embryo. 
The evanescent walls consist of broad bands of spindle fibers, 
about two-fifths of the spindle nearest the daughter nuclei dis- 
appearing very early, while the middle fifth remains long enough to 
