CHAPTER XLIV.

THE FRUIT.

I. Parts of the Fruit.

=867. After the flower comes the fruit.=—With the perfection of the fruit the seed is usually formed. This is the end towards which the energies of the plant have been directed. While the seed consists only of the ripened ovule and the contained embryo, the fruit consists of the ripened ovary in addition, and in many cases with other accessory parts, as calyx, receptacle, etc., combined with it. The wall of the ripened ovary is called a _pericarp_, and the walls of the ovary form the walls of the fruit.

=868. Pericarp, endocarp, exocarp, etc.=—This is the part of the fruit which envelops the seed and may consist of the carpels alone, or of the carpels and the adherent part of the receptacle, or calyx. In many fruits the pericarp shows a differentiation into layers, or zones of tissue, as in the cherry, peach, plum, etc. The outer, which is here soft and fleshy, is _exocarp_, while the inner, which is hard, is the _endocarp_. An intermediate layer is sometimes recognized and is called _mesocarp_. In such cases the skin of the fruit is recognized as the _epicarp_. Epicarp and mesocarp are more often taken together as exocarp.

In general fruits are _dry_ or _fleshy_. Dry fruits may be grouped under two heads. Those which open at maturity and scatter the seed are _dehiscent_. Those which do not open are _indehiscent_.

II. Indehiscent Fruits.

=869. The akene.=—The thin dry wall of the ovary encloses the single seed. It usually does not open and free the seed within. Such a fruit is an _akene_. An _akene_ is a dry, _indehiscent_ fruit. All of the crowded but separate pistils in the buttercup flower when ripe make a head of akenes, which form the fruit of the buttercup. Other examples of akenes are found in other members of the buttercup family, also in the composites, etc. The sunflower seed is a good example of an akene.

=870. The samara.=—The winged fruits of the maple, elm, etc., are indehiscent fruits. They are sometimes called key fruits.

=871. The caryopsis= is a dry fruit in which the seed is consolidated with the wall of the ovary, as in the wheat, corn, and other grasses.

=872. The schizocarp= is a dry fruit consisting of several locules (from a _syncarpous gynœcium_). At maturity the carpels separate from each other, but do not themselves dehisce and free the seed, as in the carrot family, mallow family.

=873. The acorn.=—The acorn fruit consists of the acorn and the “cup” at the base in which the acorn sits. The cup is a curious structure, and is supposed to be composed of an involucre of numerous small leaves at the base of the pistillate flower, which become consolidated into a hard cup-shaped body. When the acorn is ripe it easily separates from the cup, but the hard pericarp forming the “shell” of the acorn remains closed. Frost may cause it to crack, but very often the pericarp is split open at the smaller end by wedge-like pressure exerted by the emerging radicle during germination.

=874. The hazelnut, chestnut, and beechnut.=—In these fruits a crown of leaves (involucre) at the base of the flower grows around the nut and completely envelops it, forming the husk or burr. When the fruit is ripe the nut is easily shelled out from the husk. In the beechnut and chestnut the burr dehisces as it dries and allows the nut to drop out. But the fruit is not dehiscent, since the pericarp is still intact and encloses the seed.

=875. The hickory-nut, walnut, and butternut.=—In these fruits the “shuck” of the hickory-nut and the “hull” of the walnut and butternut are different from the involucre of the acorn or hazelnut, etc. In the hickory-nut the “shuck” probably consists partly of calyx and partly of involucral bracts consolidated, probably the calyx part predominating. This part of the fruit splits open as it dries and frees the “nut,” the pericarp being very hard and indehiscent. In the walnut and butternut the “hull” is probably of like origin as the “shuck” of the hickory nut, but it does not split open as it ripens. It remains fleshy. The walnut and butternut are often called _drupes_ or _stone-fruits_, but the fleshy part of the fruit is not of the same origin as the fleshy part of the true drupes, like the cherry, peach, plum, etc.

III. Dehiscent Fruits.

=876. Of the dehiscent fruits= several prominent types are recognized, and in general they are sometimes called _pods_. There is a single carpel (simple pistil), and the pericarp is dry (gynœcium _apocarpous_); or where there are several carpels united the pistil is compound (gynœcium _syncarpous_).

=877. The capsule.=—When the capsule is _syncarpous_ it may dehisce in three different ways: 1st. When the carpels split along the line of their union with each other longitudinally (_septicidal dehiscence_), as in the azalea or rhododendron. 2d. When the carpels _split down the middle line_ (_loculicidal dehiscence_), as in the fruit of the iris, lily, etc. 3d. When the carpels open by pores (_poricidal dehiscence_), as in the poppy. Some syncarpous capsules have but one locule, the partitions between the different locules when young having disappeared. The “bouncing-bet” is an example, and the seeds are attached to a central column in four rows corresponding to the four locules present in the young stage.

=878. A follicle= is a capsule with a single carpel which splits open along the ventral or upper suture, as in the larkspur, peony.

=879. The legume, or true pod=, is a capsule with a single carpel which splits along both sutures, as the pea, bean, etc. As the pod ripens and dries, a strong twisting tension is often produced, which splits the pod suddenly, scattering the seeds.

=880. The silique.=—In the toothwort, shepherd’s-purse, and nearly all of the plants in the mustard family the fruit consists of two united carpels, which separate at maturity, leaving the partition wall persistent. Such a fruit is a _silique_; when short it is a _silicle_, or _pouch_.

=881. A pyxidium, or pyxis=, is a capsule which opens with a lid, as in the plantain.

IV. Fleshy and Juicy Fruits.

=882. The drupe, or stone-fruit.=—In the plum, cherry, peach, apricot, etc., the outer portion (exocarp) of the pericarp (ovary) becomes fleshy, while the inner portion (endocarp) becomes hard and stony, and encloses the seed, or “pit.” Such a fruit is known as a drupe, or as a stone-fruit. In the almond the fleshy part of the fruit is removed.

=883. The raspberry and blackberry.=—While these fruits are known popularly as “berries,” they are not berries in the technical sense. Each ovary, or pericarp, in the flower forms a single small fruit, the outer portion being fleshy and the inner stony, just as in the cherry or plum. It is a _drupelet_ (little drupe). All of the drupelets together make the “berry,” and as they ripen the separate drupelets cohere more or less. It is a collection, or aggregation, of fruits, and consequently they are sometimes called _collective fruits_, or _aggregate fruits_. In the raspberry the fruit separates from the receptacle, leaving the latter on the stem, while the drupelets of the blackberry and dewberry adhere to the receptacle and the latter separates from the stem.

=884. The berry.=—In the true berry both exocarp (including mesocarp) and endocarp are fleshy or juicy. Good examples are found in cranberries, huckleberries, gooseberries, currants, snowberries, tomatoes, etc. The calyx and wall of the pistil are adnate, and in fruit become fleshy so that the seeds are imbedded in the pulpy juice. The seeds themselves are more or less stony. In the case of berries, as well as in strawberries, raspberries, and blackberries, the fruits are eagerly sought by birds and other animals for food. The seeds being hard are not digested, but are passed with the other animal excrement and thus gain dispersal.

V. Reinforced, or Accessory, Fruits.

When the torus (receptacle) is grown to the pericarp in fruit, the fruit is said to be _reinforced_. The torus may enclose the pericarps, or the latter may be seated upon the torus.

=885. In the strawberry= the receptacle of the flower becomes larger and fleshy, while the “seeds,” which are akenes, are sunk in the surface and are hard and stony. The strawberry thus differs from the raspberry and blackberry, but like them it is not a true berry.

=886. The apple, pear, quince, etc.=—In the flower the calyx, corolla, and stamens are perigynous, i.e., they are seated on the margin of the receptacle, or torus, which is elevated around the pistils. In fruit the receptacle becomes consolidated with the wall of the ovary (with the pericarp). The torus thus _reinforces_ the pericarp. The torus and outer portion of the pericarp become fleshy, while the inner portion of the pericarp becomes papery and forms the “core.” The calyx persists on the free end of the fruit. Such a fruit is called a _pome_. The receptacle, or torus, of the rose-flower, closely related to the apple, is instructive when used in comparison. The rose-fruit is called a “hip.”

=887. The pepo.=—The fruit of the squash, pumpkin, cucumber, etc., is called a _pepo_. The outer part of the fruit is the receptacle (or torus), which is consolidated with the outer part of the three-loculed ovary. The calyx, which, with the corolla and stamens, was epigynous, falls off from the young fruit.

VI. Fruits of Gymnosperms.

The fruits of the gymnosperms differ from nearly all of the angiosperms in that the seed formed from the ripened ovule is naked from the first, i.e., the ovary, or carpel, does not enclose the seed.

=888. The cone-fruit= is the most prominent fruit of the gymnosperms, as can be seen in the cones of various species of pine, spruce, balsam, etc.

=889. Fleshy fruits of the gymnosperms.=—Some of the fleshy fruits resemble the stone-fruits and berries of the angiosperms. The _cedar_ “_berries_,” for example, are fleshy and contain several seeds. But the fleshy part of the fruit is formed, not from pericarp, since there is no pericarp, but from the outer portion of the ovules, while the inner walls of the ovules form the hard stone surrounding the endosperm and embryo. An examination of the pistillate flower of the cedar (juniper) shows usually three flask-shaped ovules on the end of a fertile shoot subtended by as many bracts (carpels?). The young ovules are free, but as they grow they coalesce, and the outer walls become fleshy, forming a berry-like fruit with a three-rayed crevice at the apex marking the number of ovules. The red fleshy fruit of the yew (taxus) resembles a drupe which is open at the apex. The stony seed is formed from the single ovule on the fertile shoot, while the red cup-shaped fleshy part is formed from the outer integument of the ovule. The so-called “aril” of the young ovule is a rudimentary outer integument.

The fruit of the maidenhair tree (ginkgo) is about the size of a plum and resembles very closely a stone-fruit. But it is merely a ripened ovule, the outer layer becoming fleshy while the inner layer becomes stony and forms the pit which encloses the embryo and endosperm. The so-called “aril,” or “collar,” at the base of the fruit is the rudimentary carpel, which sometimes is more or less completely expanded into a true leaf. The fruit of cycas is similar to that of ginkgo, but there is no collar at the base. In zamia the fruit is more like a cone, the seeds being formed, however, on the under sides of the scales.

VII. The “Fruit” of Ferns, Mosses, etc.

=890. The term “fruit”= is often applied in a general or popular sense to the groups of spore-producing bodies of ferns (_fruit dots_, or _sori_), the spore-capsules of mosses and liverworts, and also to the fruit-bodies, or spore-bearing parts, of the fungi and algæ.