seen in the order Euphorbiaceae, where there are usually three such
carpels, and the fruit is termed tricoccus. In many of them, as
Hura crepitans, the cocci separate with great force and elasticity.
In many leguminous plants, such as Ornithopus, Hedysarum (fig. 17),
Entada, Coronilla and the gum-arabic plant (Acacia arabica), the
fruit becomes a schizocarp by the formation of transverse partitions
from the folding in of the sides of the pericarp, and distinct separations
taking place at these partitions.
Fruits are formed by one flower, or are the product of several flowers combined. In the former case they are either apocarpous, of one mature carpel or of several separate free carpels; or syncarpous, of several carpels, more or less completely united. When the fruit is composed of the ovaries of several flowers united, it is usual to find the bracts and floral envelopes also joined with them, so as to form one mass; hence such fruits are known as multiple, confluent or anthocarpous. The term simple is applied to fruits which are formed by the ovary of a single flower, whether they are composed of one or several carpels, and whether these carpels are separate or combined.
 Fig. 19. |
Fig. 21. From Vines’ Students’ Text-Book of Botany, by permission of Swan Sonnenschein & Co. |
 Fig. 20. | |
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Fig. 19.—Dry one-seeded fruit of dock (Rumex) cut vertically. ov, Pericarp formed from ovary wall; s, seed; e, endosperm; pl, embryo with radicle pointing upwards and cotyledons downwards—enlarged. | |
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Fig. 20.—Achene of Ranunculus arvensis in longitudinal section; e, endosperm; pl, embryo. (After Baillon, enlarged.) From Strasburger’s Lehrbuch der Botanik, by permission of Gustav Fischer. | |
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Fig. 21.—Fruit of Common Sycamore (Acer Pseudoplatanus), dividing into two mericarps m; s, pedicel; fl, wings (nat. size). | |
The object of the fruit in the economy of the plant is the protection
and nursing of the developing seed and the dispersion of the ripe
seeds. Hence, generally, one-seeded fruits are indehiscent,
while fruits containing more than one seed open to allow
of the dispersal of the seeds over as wide an area as
Dispersal
of fruit or seed.
possible. The form, colour, structure and method of
dehiscence of fruits and the form of the contained seeds are intimately
associated with the means of dispersal, which fall into several
categories. (1) By a mechanism residing in the fruit. Thus many
fruits open suddenly when they are dry, and the seeds are ejected
by the twisting or curving of the valves, or in some other way;
e.g. in gorse, by the spiral curving of the valves; in Impatiens, by
the twisting of the cocci; in squirting cucumber, by the pressure
exerted on the pulpy contents by the walls of the pericarp. (2)
By aid of various external agencies such as water. Fruits or seeds
are sometimes sufficiently buoyant to float for a long time on sea- or
fresh-water; e.g. coco-nut, by means of its thick, fibrous coat
(mesocarp), is carried hundreds of miles in the sea, the tough,
leathery outer coat (epicarp) preventing it from becoming water-soaked.
Fruits and seeds of West Indian plants are thrown up on
the coasts of north-west Europe, having been carried by the Gulf
Stream, and will often germinate; many are rendered buoyant by
air-containing cavities, and the embryo is protected from the sea-water
by the tough coat of fruit or seed. Water-lily seeds are
surrounded with a spongy tissue when set free from the fruit, and
float for some distance before dropping to the bottom. (3) The
most general agent in the dispersal of seeds is the wind or currents
of air—the fruit or seed being rendered buoyant by wing-developments
as in fruits of ash (fig. 1) or maple (fig. 21), seeds of pines
and firs, or many members of the order Bignoniaceae; or hair-developments
as in fruits of clematis, where the style forms a feathery
appendage, fruits of many Compositae (dandelion, thistle, &c.),
which are crowned by a plumose pappus, or seeds of willow and
poplar, or Asclepias (fig. 36), which bear tufts of silky hairs; to
this category belong bladder-like fruits, such as bladder-senna,
which are easily rolled by the wind, or cases like the so-called rose
of Jericho, a small cruciferous plant (Anastatica hierocuntica), where
the plant dries up after developing its fruits and becomes detached
from the ground; the branches curl inwards, and the whole plant is
rolled over the dry ground by the wind. The wind also aids the
dispersal of the seeds in the case of fruits which open by small teeth
(many Caryophyllaceae [fig. 6]) or pores (poppy [fig. 7], Campanula,
&c.); the seeds are in these cases small and numerous, and are jerked
through the pores when the capsules, which are generally borne on
long, dry stems or stalks, are shaken by the wind. (4) In other cases
members of the animal world aid in seed-dispersal. Fruits often
bear stiff hairs or small hooks, which cling to the coat of an animal
or the feathers of a bird; such are fruits of cleavers (Galium Aparine),
a common hedge-row plant, Ranunculus arvensis (fig. 20), carrot,
Geum, &c.; or the fruit or seed has an often bright-coloured, fleshy
covering, which is sought by birds as food, as in stone-fruits such as
plum, cherry (fig. 5), &c., where the seed is protected from injury
in the mouth or stomach of the animal by the hard endocarp; or
the hips of the rose (fig. 3), where the succulent scarlet “fruit”
(the swollen receptacle) envelops a number of small dry true fruits
(achenes), which cling by means of stiff hairs to the beak of the bird.
 Fig. 22. |
 Fig. 23. |
 Fig. 25. |
 Fig. 24. | ||
|
Fig. 22.—Vertical section of a grain of wheat, showing embryo below at the base of the endosperm e; s, scutellum separating embryo from endosperm; f.l, foliage leaf; p.s, sheath of plumule; p.r, primary root; s.p.r, sheath of primary root. | ||
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Fig. 23.—Fruit of Comfrey (Symphytum) surrounded by persistent calyx, c. The style s appears to arise from the base of the carpels, enlarged. | ||
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Fig. 24.—Ovary of Foeniculum officinale with pendulous ovules, in longitudinal section. (After Berg and Schmidt, magnified.) From Strasburger’s Lehrbuch der Botanik, by permission of Gustav Fischer. | ||
|
Fig. 25.—Fruit of Carum Carui. A, Ovary of the flower; B, ripe fruit. The two carpels have separated so as to form two mericarps (m). Part of the septum constitutes the carpophore (a). p, Top of flower-stalk; d, disk on top of ovary; n, stigma. From Vines’ Students’ Text-Book of Botany, by permission of Swan Sonnenschein & Co. | ||
Simple fruits have either a dry or succulent pericarp. The achene is a dry, one-seeded, indehiscent fruit, the pericarp of which is closely applied to the seed, but separable from it. It is solitary, forming a single fruit, as in the dock (fig. 19) and in the cashew, where it is supported on a fleshy peduncle; or Forms of fruit. aggregate, as in Ranunculus (fig. 20), where several achenes are placed on a common elevated receptacle. In the strawberry the achenes (fig. 2) are aggregated on a convex succulent receptacle. In the rose they are supported on a concave receptacle (fig. 3), and in the fig the succulent receptacle completely encloses the achenes (fig. 4). In Dorstenia the achenes are situated on a flat or slightly concave receptacle. Hence what in common language are called the seeds of the strawberry, rose and fig, are in reality ripe carpels. The styles occasionally remain attached to the achenes in the form of feathery appendages, as in Clematis. In Compositae, the fruit is an inferior achene (cypsela), to which the pappus (modified calyx) remains adherent. Such is also the nature of the fruit in Dipsacaceae (e.g. scabious). When the pericarp is thin, and appears like a bladder surrounding the seed, the achene is termed a utricle, as in Amarantaceae. When the pericarp is extended in the form of a winged appendage, a samara or samaroid achene is produced, as in the ash (fig. 1) and common sycamore (fig. 21). In these cases there are usually two achenes united, one of which, however, as in Fraxinus (fig. 1), may be abortive. The wing surrounds the fruit longitudinally in the elm. When the pericarp becomes so incorporated with the seed as to be inseparable from it, as in grains of wheat (fig. 22), maize, oats and other grasses, then the name caryopsis is given. The one-seeded portions (mericarps) of schizocarps often take the form of achenes, e.g. the mericarps of the
