317. =Ovule= (from the Latin, meaning a little egg) is the technical
name of that which in the flower answers to and becomes the seed.
[Illustration: Fig. 340. A cluster of ovules, pendulous on their
funicles.]
318. Ovules are _naked_ in gymnospermous plants (as just described), in
all others they are enclosed in the ovary. They may be produced along
the whole length of the cell or cells of the ovary, and then they are
apt to be numerous, or only from some part of it, generally the top or
the bottom. In this case they are usually few or single (_solitary_, as
in Fig. 341-343). They may be _sessile_, i. e. without stalk, or they
may be attached by a distinct stalk, the FUNICLE or FUNICULUS (Fig.
340).
[Illustration: Fig. 341. Section of the ovary of a Buttercup,
lengthwise, showing its ascending ovule.]
[Illustration: Fig. 342. Section of the ovary of Buckwheat, showing the
erect ovule.]
[Illustration: Fig. 343. Section of the ovary of Anemone, showing its
suspended ovule.]
319. Considered as to then position and direction in the ovary, they are
_Horizontal_, when they are neither turned upward nor downward, as in
Podophyllum (Fig. 326),
_Ascending_, when rising obliquely upwards, usually from the side of the
cell, not from its very base, as in the Buttercup (Fig. 341), and the
Purslane (Fig. 272),
_Erect_, when rising upright from the very base of the cell, as in the
Buckwheat (Fig. 342),
_Pendulous_, when hanging from the side or from near the top, as in the
Flax (Fig. 270), and
_Suspended_, when hanging perpendicularly from the very summit of the
cell, as in the Anemone (Fig. 343). All these terms equally apply to
seeds.
320. In structure an ovule is a pulpy mass of tissue, usually with one
or two coats or coverings. The following parts are to be noted, viz.--
KERNEL or NUCLEUS, the body of the ovule. In the Mistletoe and some
related plants, there is only this nucleus, the coats being wanting.
TEGUMENTS, or coats, sometimes only one, more commonly two. When two,
one has been called PRIMINE, the other SECUNDINE. It will serve all
purposes to call them simply outer and inner ovule coats.
ORIFICE, or FORAMEN, an opening through the coats at the organic apex of
the ovule. In the seed it is _Micropyle_.
CHALAZA, the place where the coats and the kernel of the ovule blend.
HILUM, the place of junction of the funiculus with the body of the
ovule.
[Illustration: Fig. 344. Orthotropous ovule of Buckwheat: _c_, hilum
and chalaza; _f_, orifice.]
[Illustration: Fig. 345. Campylotropous ovule of a Chickweed: _c_, hilum
and chalaza; _f_, orifice.]
[Illustration: Fig. 346. Amphitropous ovule of Mallow: _f_, orifice;
_h_, hilum; _r_, rhaphe; _c_, chalaza.]
[Illustration: Fig. 347. Anatropous ovule of a Violet, the parts
lettered as in the last.]
321. =The Kinds of Ovules.= The ovules in their growth develop in three
or four different ways and thereby are distinguished into
_Orthotropous_ or _Straight_, those which develop without curving or
turning, as in Fig. 344. The chalaza is at the insertion or base, the
foramen or orifice is at the apex. This is the simplest, but the least
common kind of ovule.
_Campylotropous_ or _Incurved_, in which, by the greater growth of one
side, the ovule curves into a kidney-shaped outline, so bringing the
orifice down close to the base or chalaza; as in Fig. 345.
_Amphitropous_ or _Half Inverted_, Fig. 346. Here the forming ovule,
instead of curving perceptibly, keeps its axis nearly straight, and, as
it grows, turns round upon its base so far as to become transverse to
its funiculus, and adnate to its upper part for some distance. Therefore
in this case the attachment of the funiculus or stalk is about the
middle, the chalaza is at one end, the orifice at the other.
[Illustration: Fig. 348-350. Three early stages in the growth of ovule
of a Magnolia, showing the forming outer and inner coats which even in
the later figure have not yet completely enclosed the nucleus; 351,
further advanced, and 352, completely anatropous ovule.]
[Illustration: Fig. 353. Longitudinal section, and 354, transverse
section of 352.]
[Illustration: Fig. 355. Same as 353, enlarged showing the parts in
section: _a_, outer coat; _b_, inner coat; _c_, nucleus; _d_, rhaphe.]
_Anatropous_ or _Inverted_, as in Fig. 347, the commonest kind, so
called because in its growth it has as it were turned over upon its
stalk, to which it has continued adnate. The organic base, or chalaza,
thus becomes the apparent summit, and the orifice is at the base, by
the side of the hilum or place of attachment. The adnate portion of the
funiculus, which appears as a ridge or cord extending from the hilum to
the chalaza, and which distinguishes this kind of ovule, is called the
RHAPHE. The amphitropous ovule (Fig. 346) has a short or incomplete
rhaphe.
322. Fig. 348-352 show the stages through which an ovule becomes
anatropous in the course of its growth. The annexed two figures are
sections of such an ovule at maturity; and Fig. 355 is Fig. 353
enlarged, with the parts lettered.