of an ovule. The nucleus of the tube-cell has meanwhile passed into
the tube, as does also the generative nucleus which divides to
form two male- or sperm-cells. The male-cells are carried to their
destination in the tip of the pollen-tube.

[v.02 p.0011]


_Pistil and embryo-sac._

The ovary contains one or more ovules borne on a placenta, which is
generally some part of the ovary-wall. The development of the ovule,
which represents the macrosporangium, is very similar to the
process in Gymnosperms; when mature it consists of one or two coats
surrounding the central nucellus, except at the apex where an opening,
the micropyle, is left. The nucellus is a cellular tissue enveloping
one large cell, the embryo-sac or macrospore. The germination of the
macrospore consists in the repeated division of its nucleus to form
two groups of four, one group at each end of the embryo-sac. One
nucleus from each group, the polar nucleus, passes to the centre of
the sac, where the two fuse to form the so-called definitive nucleus.
Of the three cells at the micropylar end of the sac, all naked cells
(the so-called egg-apparatus), one is the egg-cell or oosphere, the
other two, which may be regarded as representing abortive egg-cells
(in rare cases capable of fertilization), are known as synergidae.
The three cells at the opposite end are known as antipodal cells
and become invested with a cell-wall. The gametophyte or prothallial
generation is thus extremely reduced, consisting of but little more
than the male and female sexual cells--the two sperm-cells in the
pollen-tube and the egg-cell (with the synergidae) in the embryo-sac.