The Elements of Botany Part 16

[Ill.u.s.tration: Fig. 342. Section of the ovary of Buckwheat, showing the erect ovule.]

[Ill.u.s.tration: 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 b.u.t.tercup (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 ma.s.s 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.

[Ill.u.s.tration: Fig. 344. Orthotropous ovule of Buckwheat: _c_, hilum and chalaza; _f_, orifice.]

[Ill.u.s.tration: Fig. 345. Campylotropous ovule of a Chickweed: _c_, hilum and chalaza; _f_, orifice.]

[Ill.u.s.tration: Fig. 346. Amphitropous ovule of Mallow: _f_, orifice; _h_, hilum; _r_, rhaphe; _c_, chalaza.]

[Ill.u.s.tration: 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.

[Ill.u.s.tration: 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.]

[Ill.u.s.tration: Fig. 353. Longitudinal section, and 354, transverse section of 352.]

[Ill.u.s.tration: 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.

Section XII. MODIFICATIONS OF THE RECEPTACLE.

[Ill.u.s.tration: Fig. 356. Longitudinal section of flower of Silene Pennsylvanica, showing stipe between calyx and corolla.]

[Ill.u.s.tration: Fig. 357. Flower of a Cleome of the section Gynandropsis, showing broadened receptacle to bear petals, lengthened stipe below the stamens, and another between these and pistil.]

[Ill.u.s.tration: Fig. 358. Pistil of Geranium or Cranesbill.]

[Ill.u.s.tration: Fig. 359. The same, ripe, with the five carpels splitting away from the long beak (carpoph.o.r.e), and hanging from its top by their recurving styles.]

323. =The Torus= or Receptacle of the flower (237, Fig. 223) is the portion which belongs to the stem or axis. In all preceding ill.u.s.trations it is small and short. But it sometimes lengthens, sometimes thickens or variously enlarges, and takes on various forms.

Some of these have received special names, very few of which are in common use. A lengthened portion of the receptacle is called

A STIPE. This name, which means simply a trunk or stalk, is used in botany for various stalks, even for the leaf-stalk in Ferns. It is also applied to the stalk or petiole of a carpel, in the rare cases when there is any, as in Goldthread. Then it is technically distinguished as a THECAPh.o.r.e. When there is a stalk, or lengthened internode of receptacle, directly under a compound pistil, as in Stanleya and some other Cruciferae, it is called a GYNOPh.o.r.e. When the stalk is developed below the stamens, as in most species of Silene (Fig. 356), it has been called an ANTHOPh.o.r.e or GONOPh.o.r.e. In Fig. 357 the torus is dilated above the calyx where it bears the petals, then there is a long internode (gonoph.o.r.e) between it and the stamens; then a shorter one (gynoph.o.r.e) between these and the pistil.

324. =A Carpoph.o.r.e= is a prolongation of receptacle or axis between the carpels and bearing them. Umbelliferous plants and Geranium (Fig. 358, 359) afford characteristic examples.

[Ill.u.s.tration: Fig. 360. Longitudinal section of a young strawberry, enlarged.]

[Ill.u.s.tration: Fig. 361. Similar section of a young Rose-hip.]

[Ill.u.s.tration: Fig. 362. Enlarged and top-shaped receptacle of Nelumbium, at maturity.]

325. Flowers with very numerous simple pistils generally have the receptacle enlarged so as to give them room; sometimes becoming broad and flat, as in the Flowering Raspberry, sometimes elongated, as in the Blackberry, the Magnolia, etc. It is the receptacle in the Strawberry (Fig. 360), much enlarged and pulpy when ripe, which forms the eatable part of the fruit, and bears the small seed-like pistils on its surface.

In the Rose (Fig. 361), instead of being convex or conical, the receptacle is deeply concave, or urn-shaped. Indeed, a Rose-hip may be likened to a strawberry turned inside out, like the finger of a glove reversed, and the whole covered by the adherent tube of the calyx. The calyx remains beneath in the strawberry.

326. In Nelumbium, of the Water-Lily family, the singular and greatly enlarged receptacle is shaped like a top, and bears the small pistils immersed in separate cavities of its flat upper surface (Fig. 362).

[Ill.u.s.tration: Fig. 363. Hypogynous disk in Orange.]

327. =A Disk= is an enlarged low receptacle or an outgrowth from it, _hypogynous_ when underneath the pistil, as in Rue and the Orange (Fig.

363), and _perigynous_ when adnate to calyx-tube (as in Buckthorn, Fig.

364, 365), and Cherry (Fig. 271), or to both calyx-tube and ovary, as in Hawthorn (Fig. 273). A flattened hypogynous disk, underlying the ovary or ovaries, and from which they fall away at maturity, is sometimes called a GYn.o.bASE, as in the Rue family. In some Borragineous flowers, such as Houndstongue, the gyn.o.base runs up in the centre between the carpels into a carpoph.o.r.e. The so-called _epigynous_ disk (or STYLOPODIUM) crowning the summit of the ovary in flowers of Umbelliferae, etc., cannot be said to belong to the receptacle.

[Ill.u.s.tration: Fig. 364. Flower of a Buckthorn showing a conspicuous perigynous disk.]

[Ill.u.s.tration: Fig. 365. Vertical section of same flower.]

Section XIII. FERTILIZATION.