removed from
the slide and upper surface of the cover glass. It is generally best
to gently wipe the edge of the cover glass with a small brush
moistened with alcohol before applying the cement.

[Illustration: FIG. 127.--_A_, pollen mother cell of the wild onion.
_n_, nucleus. _B-F_, early stages in the division of the nucleus.
_par._ nucleolus; acetic acid, gentian violet, x 350.]

If the spore mother cells are still quite young, we shall find the
nucleus (Fig. 127, _A_, _n_) comparatively small, and presenting a
granular appearance when strongly magnified. These granules, which
appear isolated, are really parts of filaments or segments, which
are closely twisted together, but scarcely visible in the resting
nucleus. On one side of the nucleus may usually be seen a large
nucleolus (called here, from its lateral position, paranucleus), and
the whole nucleus is sharply separated from the surrounding
protoplasm by a thin but evident membrane.

The first indication of the approaching division of the nucleus is
an evident increase in size (_B_), and at the same time the colored
granules become larger, and show more clearly that they are in lines
indicating the form of the segments. These granules next become more
or less confluent, and the segments become very evident, appearing
as deeply stained, much-twisted threads filling the nuclear cavity
(Fig. 127, _C_), and about this time the nucleolus disappears.

The next step is the disappearance of the nuclear membrane so that
the segments lie apparently free in the protoplasm of the cell. They
arrange themselves in a flat plate in the middle of the cell, this
plate appearing, when seen from the side, as a band running across
the middle of the cell. (Fig. 127, _D_, shows this plate as seen
from the side, _E_ seen from above.)

About the time the nuclear plate is complete, delicate lines may be
detected in the protoplasm converging at two points on opposite
sides of the cell, and forming a spindle-shaped figure with the
nuclear plate occupying its equator. This stage (_D_), is known as
the "nuclear spindle." The segments of the nuclear plate next divide
lengthwise into two similar daughter segments (_F_), and these then
separate, one going to each of the new nuclei. This stage is not
always to be met with, as it seems to be rapidly passed over, but
patient search will generally reveal some nuclei in this