Fruit, a term used generally in a very loose sense for the structures that follow the flower in the higher plants, especially when they are succulent or sweet, and sometimes extended even to other parts of the plant. A strawberry, a mulberry, a fig, or a pineapple are usually called fruits, and even a tart made from the leaf-stalks of the rhubarb is sometimes thought of as a fruit-tart, whilst we hesitate to apply the term fruit to a nut, a pea-pod, a grain of corn, a poppy-head, or a vegetable marrow. Botanically, however, a fruit may be best defined as the fertilised gynteceum of a flower, together with those adjacent structures (belonging to the same flower) that enlarge and adhere to it in consequence of fertilisation. Such "polythalamic "structures as the mulberry, the fig, and the pine-apple, which not only involve other parts than the gynseceum, but are also each made up of many flowers, may well be kept apart i.nder the name of infruitescences (q.v.). Among "monothalamic" structures - i.e. those formed from a single flower, we may distinguish true fruits, those consisting solely of gyntoceal structures, from pseudocarps, those to which other parts contribute. The walls of the fertilised ovary in the former are termed the pericarp, and this consists of three layers often readily distinguishable, the epicarp (q.v.), mesocarp (q.v.), and endocarp (q.v.). In pseudocarps the other structures contributing to the fruit are mainly derived from the floral receptacle. In the strawberry (q.v.), for instance, the numerous carpels, constituting the apocarpous (q.v.) and polycarpellary gynaeceum are scattered spirally over a fleshy outgrowth from the conical white receptacle. No such structure is present in the buttercup or the raspberry, or even in the closely-related genus Potentilla. In the rose (q.v.) the dry, apocarpous, one-seeded carpels are enclosed in a red, fleshy, urn-shaped, receptacular tube. In the apple, the cucumber, and all fruits formed from "inferior" ovaries, the true fruit or gynaeceum is surrounded by the adherent receptacular tube, which often forms much of the fleshy portion. The terms pericarp, epicarp, mesocarp, and endocarp can hardly be properly applied to these pseudocarpic structures.
After fertilisation (q.v.), or even after pollination, the ovary or ovaries commonly increase in size; and, whilst the petals, stamens, and sometimes the sepals, fall off, nourishment is determined towards the gynaeceum. This enlargement of the ovary sometimes takes place, mainly among cultivated races of plants, without fertilisation, as in the sultana raisin and in the seedless varieties of the apple and of the Maltese orange. In annuals, biennials, and those other plants, such as Aloe and Agave (q.v.), which, producing only one crop of flowers and fruit in their lives, are termed menocarpic, as the fruit ripens the whole plant withers, exhausted by the great physiological effort of seed production. In ripening, the ovary or other structures either dry up or wither, like autumn leaves, or become fleshy. In the former case the fruit, if containing more than one seed, is commonly dehiscent, splitting, that is, either into one-seeded portions or cocci, which do not themselves split [Schizocarp], or so as to discharge its seeds. Fleshy fruits, on the other hand, are mainly indehiscent. They commonly change colour, turning from green to some shade of red, yellow, or, more rarely, purple, by modification of their chlorophyll (q.v.), and at the same time convert much of their acid contents into sugar.
Some fruits are furnished with wing-like projections of the pericarp [Samara], and others with a "pappus" of hairs [Cypsela], by means of which they are carried by the wind beyond the stifling shade of the parent plant. Some dehiscent fruits - such as those of the balsams, and, to a less extent, broom and furze - split so elastically as to throw their seed some little distance. Fruit-eating birds do not, as a, rule, have muscular gizzards, and frequently swallow seeds whole and pass them undigested; but, whilst their seeds are almost always indigestible, succulent fruits, such as apples, are attractive to other animals besides birds - deer, for example. Even the dry fruits of grasses have been observed to be thus disseminated, after being swallowed, by locusts. Many fruits are furnished with curved hooks, which become entangled in the wool or hair of animals, and may thus cause them to be conveyed long distances; whilst the stony pericarp of some fruits will for some time resist the action of sea-water.