538 
THE DICTIONARY OF GARDENING, 
Ovule—continued. : 
that remains straight from its earliest appearance till 
its full maturity, such as is found in the Docks and 
the Buckwheat. The Ovule first appears like a small, 
2 
Fic. 801. THREE STAGES IN GROWTH OF ORTHOTROPOUS OVULE. 
. A, Nucellus alone; B, Inner Coat; C, Both Coats growing 
up to cover Nucellus. 
rounded or egg-shaped swelling (see A, Fig. 801), on the 
placenta, made up of cells alike in form and contents. 
This body is usually termed the “nucleus of the Ovule ; 
but the term “nucellus,” now coming into use, is prefer- 
able, since “ nucleus” should be oe - the ere 
the protoplasm of living cells generally known under 
a, nea, Round the oe ot the nucellus a cellular 
ring (see B, Fig. 801), soon begins to appear, and con- 
tinues to grow up to form a thin covering around that 
body. But, while this has been growing, another cover- 
ing (see C, Fig. 801), forms over it also from below 
upwards, and the two grow till they leave only a 
minute opening through them at the upper end (i.e., 
farthest from the placenta), called the “micropyle,” 
which allows the entrance of a slender tube from the 
pollen grain. The two coverings are named the inner 
and the outer coats. At the end next the placenta (see 
FId. 802. ORTHOTROPOUS OVULE IN SECTION, showing Two Coats. 
Fig. 802), there is, generally, a narrower neck, or there 
may be a well-formed stalk, or funiculus ; though some- 
times there is no visible stalk, the Ovule being sessile, 
or fixed by a broad base. From the woody, or fibro- 
vascular, bundle in the placenta, a branch runs into the 
stalk of the Ovule. The part of the Ovule where the 
coats are grown to the nucellus is the chalaza. At this 
part, separation takes place when the seed is ripe, and 
falls from the stalk; and a scar is left, known as the 
hilum. In the nucellus, a change goes on which results 
in the formation of a cell—the embryo-sac—very much 
larger than the others. It lies near the micropyle, from 
which, in most Ovules, it is separated by one or two 
layers of cells of the nucellus. It may be almost as long 
aa the nucellus, and may, in course of growth, crush the 
latter, until all its tissue disappears. 
This cell is full of protoplasm; and in the latter may 
be seen several bodies, as follows (see Fig. 803): At the 
end next the micropyle are three cells, viz., two rather 
long ones, known as helper cells; and, at their lower end, 
a round cell—the embryonal vesicle—from which the 
embryo is afterwards developed. At the opposite end 
of the embryo-sac lie three small bodies—the antipodal 
cells—the use of which is unknown. They are believed 
to represent a structure that plays an important part 
in the development of Ferns and their allies, but that 
Ovule—continued. 
has become superseded in the higher plants. In the 
protoplasm between them lie one or two nuclei, which 
have to assist in the formation of the endosperm while 
Fig. 803, EMBRYO SAC OF ANGIOSPERM BEFORE FERTILISATION, 
IN THREE STAGES, showing (h) Helper Cells, (e. v.) Embryonal 
Vesicle, (a) Antipodal Cells, and (n, n) Nuclei. In A, the 
Helper and Anti Cells, and the Embryonal Vesicle, are 
5 angular, and the two Nuclei are wide apart; in B, the 
Embryonal Vesicle is rounded, and the Nuclei lie close to- 
gether; in C, the Embryonal Vesicle is ready to be fertilised ; 
e two Nuclei are united to form one, and the Antipodal, as 
well as the Helper Cells, are rounded off. 
the embryo, or young plant, is being formed. A brief 
account of the development of the Ovule into the seed 
will help to make these various structures more in- 
telligible. 85 
When the stigma is ready to receive the pollen grains, 
and one of these is placed upon it, the grain very soon, 
in most plants, pushes a slender pollen tube between 
the cells of the stigma, down the loose “ conducting 
tissue” of the style, and into the cavity of the ovary, 
where it finds its way to the micropyle of an Ovule. 
Passing down this, it pushes the thin coat of the embryo- 
sac before it, presses between the helper cells, and reaches 
the embryonal vesicle. It is believed that a part of 
the protoplasm passes from the tube into one of the 
helper cells, which then acts in turn upon the vesicle. 
The helper cells, and, probably, the antipodal cells, dis- 
appear; and the embryonal vesicle begins to grow, and 
to be divided by cell-walls, so that a rounded mass of 
tissue is formed, attached above to a row of cells, or 
to a mass in some plants, called the suspensor. The 
lower rounded mass is the embryo, which increases in 
size, and shows beginnings of the axis and leaves, or 
cotyledons. These parts can easily be made out in most 
plants. In the meanwhile, after fertilisation has been 
effected, the nuclei in the protoplasm begin to divide, 
and to form new nuclei, around which cells form, and 
the embryo-sac becomes filled, more or less completely, 
with cellular endosperm. This may disappear in the 
ripening of the seed (e.g., in Beans); or it may remain, 
and may form a large part of the seed (e.g., in Wheat), 
5 case it is often called the albumen of the 
DEVIATIONS FROM THE ABOVE TYPE OF STRUCTURE 
AND DEVELOPMENT. 
Structure. In many plants (e.g., Actea, Composite, 
&c.) there is only one coat on the Ovule (see Fig. 804); 
in a few (e.g., Mistletoe) there is no coat, the nucellus 
being exposed in the cavity of the ovary. The funiculus 
