The fruit of a plant (in the case of our flowering plants) consists of the matured pistil (or gynoecium), including also whatever parts of the perianth or other floral organs may be joined to it. Fruits are of various degrees of simplicity or complexity, and may consist of a matured simple ovary, a cluster of such ovaries, at least when they are somewhat coherent, or a ripened ovary with calyx and other floral parts consolidated with it.
The pericarp, or seed vessel, is the ripened ovary and should therefore accord in structure with the ovary from which it is derived. In the development of a simple ovary into a simple fruit certain alterations sometimes take place, either by the abortion or obliteration of certain parts, or by accessory growth. The dehiscence is the method by which a pericarp opens to discharge its seeds and may be regular (normal) or irregular (abnormal). The word " pod " is frequently applied to dehiscent pericarps.
A capsule is a dehiscent pericarp formed of two or more carpels. Such carpels are septicidal (figure 80) when the dehiscence is such that the carpel is divided into its constituent carpels. Members of the St John's-wort family afford a good example of this method as do also Rhododendron and Kalmia. Carpels are called loculicidal (figure 79) when each of the component carpels splits down its dorsal suture, as in Iris, Hibiscus, Oenothera etc.
Kinds of fruits. For ordinary purposes it is sufficient to classify fruits into four classes:
1 Simple fruits, those which result from the ripening of a single pistil.
2 Aggregate, those of a cluster of carpels of one flower crowded into a mass.
3 Accessory fruits, where the principal mass consists of the surroundings or support of either a simple or an aggregate fruit.
4 Multiple or collective fruits, formed by the union or compact aggregation of the pistils of several flowers.
1 Simple Fruits
Upon the basis of texture, simple fruits may be designated as dry fruits, stone fruits and baccate fruits.
Dry fruits which are dehiscent:
Follicle (figure 78), a pod formed by a simple pistil, and dehiscent along one line (suture, and almost always the inner or ventral suture), as in the Columbine, Marsh Marigold, Milkweed and Dogbane.
Legume (figure 77), a pod formed of a simple pistil which is dehiscent by both sutures, so dividing it into two pieces or valves. The fruits of the Bean or Pea family are of this sort. Some members of this family (Meibomia), however, have legumes reduced to indehiscent achenes, joined together end to end, and to which a special term "loment" (figure 76) is applied.
Capsule (figures 79 and So), a pod or dehiscent fruit, of any compound pistil. The modes of regular dehiscence are mentioned above in the paragraph on dehiscence, and it remains here to describe two modifications of the capsule, namely, the pyxis, in which the dehiscence is along a circular line, cutting off the upper part as a lid, examples of which are seen in the common Plantain, Purslane and Henbane, small plants or weeds not illustrated in this work; and the silique, a narrow, two-valved capsule, with two parietal placentae, from which the valves separate in dehiscence, as in the Mustard family, where there is usually a false partition stretched across between the two placentae. Dry fruits which are indehiscent:
Samara, an indehiscent, one-seeded fruit provided with a wing. In the Ash, the wing is terminal; in the Elm, the wing surrounds the body of the pericarp; and the Maple fruit is a double samara or pair of such fruits.
Achene (figures 81-88), a general term for all one-seeded, dry and hard, seedlike fruits. The best examples are the fruits of the Buttercup, Anemone, Clematis and Avens. The style sometimes remains on the fruit as a long and feathery tail (Dandelion, figure 85), and in others merely as a short hook (Buttercup, figures 86 and 87). In the Compositae (Sunflower family) the tube of the calyx is joined with the surface of the ovary, and its border or upper edge appears as a crown or cup, or a set of teeth or of scales, or very often as a tuft of bristles or hairs, called the pappus (figures 82-84,88)
Utricle, a dry achenelike fruit with a thin and bladdery loose pericarp, like that of the Goosefoot (Chenopodium).
Caryopsis or grain, differs from the achene in having the seed completely filling the cell and its thin coats firmly consolidated throughout with the very thin pericarp. This term is applied to the fruits of the grass family, including Indian corn and all other cereals.
Nut, a hard one-celled and one-seeded, indehiscent fruit which finds its best examples in the fruit of the Hazel, Beech, Oak, Chestnut etc. The smaller nutlike fruits of the Borrage family and of the Mint family are usually called nutlets.
Drupe (figures 90 and 92), of which the best examples are the fruit of the Cherry, Plum, Peach etc., are one-seeded or rarely two-seeded, in the ripening of which the outer portion of the pericarp becomes fleshy or pulpy and the inner portion becomes much hardened. The term is also commonly applied to similar fruits of the Hackberry, Cornus, Rhamnus etc. In the case of the Blackberry (figure 89) and Raspberry, the several pericarps of the aggregate fruit are called drupelets.
Pome (figure 91), the name of the fruit of the Apple, Pear, Quince etc., which are fleshy fruits, composed of two to several carpels, of parchmentlike texture (or hard in the Thorn Apples), inclosed in flesh which has developed from the inclosing calyx and receptacle. Indeed, the fruit of the Thorn Apple might well be called a " several-seeded drupe."
Pepo, or Gourd-fruit, a type of fruit typified by the Melon, Squash, Cucumber, Gourd and other members of that family.
Berry [baccate] (figure 93), a simple fruit in which the pericarp is fleshy throughout and without a hardened inner coat. The fruit of the Grape, Currant, Gooseberry, Cranberry, Banana and Tomato furnish good examples.
2 Aggregate Fruits
Aggregate fruits are those in which a cluster of carpels, all belonging to one flower, are crowded on the receptacle into one mass, as in the Blackberry (figure 89) taken as a whole. They may be aggregates of any kind of simple fruits. But when dry and not coherent, the mass would simply be described as a head or spike of carpels (or achenes, as in Buttercup, Anemone etc.).
3 Accessory Fruits Accessory fruits are those in which some conspicuous part of the fruit is derived from some portion not organically connected with the ovary or pistil. This part might be called a pseudocarp, and this condition may occur either in simple, in aggregate, or in multiple fruits. The Winter-green (Gaultheria procumbens) affords a good example (figures 94 and 95), the fleshy part of the fruit being the enlarged calyx. Likewise the torus, although not conspicuous, may be said to be an accessory part of the fruit of the Blackberry, being the fleshy or pulpy center of the fruit. In the Strawberry it is very conspicuous and comprises the sole edible part of the fruit, the achenes or true fruits being dispersed over the surface and comparatively insignificant.
4 Multiple or Collective Fruits Multiple or collective fruits are those which result from the aggregation of several flowers into one mass. The simplest of these is the fruit of the Partridge Berry (Mitchella repens) and certain Honeysuckles (-Loni-cera) formed of the ovaries of two blossoms united into one fleshy fruit. More typical examples of this are seen in the Pineapple fruit, the Mulberry and others.