547. The pericarp (περí, around) is the envelope of the seeds, consisting of the carpels and whatever other parts they may be combined with. It varies greatly in texture and substance when mature, being then either dry, as the pea-pod, or succulent, as the currant. Dry pericarps are membranous, or coriaceous (leathery), or woody. Succulent pericarps may he either wholly so, as the grape, or partly so, as the peach and other stone fruit.
548. Pericarp closed or open. With very few exceptions the pericarp encloses the seed while maturing. In mignonette (322), however, it opens, exposing the seed, immediately after flowering. The memhranous pericarp of cohosh (Leontice) falls away early leaving the seed to ripen naked. In yew (Taxus) the seed is never enclosed wholly by its fleshy pericarp; hut in most of the other Coniferae, the close-pressed, carpellary scales cover the seeds. One-seeded fruits, like those of butter-cups, etc., are liable to be mistaken for naked seeds.
549. Dehiscence. The fleshy pericarp is always indehiscent. Its seeds are liberated only by its decay, or bursting in germination. So also in many cases the dry pericarp, as the acorn. But more commonly the dry fruit, when arrived at maturity, opens in some way, discharging its seeds. Such fruits are dehiscent.
550. Modes. Dehiscence is either valvular, porous, or circumscis-sile; valvular, when the pericarp opens vertically along the sutures, forming regular parts called valves. These valves may separate quite to the base, or only at the top, forming teeth, as in chickweed. We notice four modes of valvular dehiscence, viz.
1, Sutural, when it takes place at the sutures of any 1-celled pericarp, as columbine, pea, violet.
Dehiscence; 429, septicidal; 430, loculicidal; 481, septifragal.
2, Septicidal (septum, partition, caedo, to cut), when it takes place through the dissepiments (which are double, § 525). The carpels thus separated may open severally by sutures, (Mallows), or remain indehiscent, as in Vervain.
3, Loculicidal (loculus, a cell, caedo, to cut), when each carpel opens at its dorsal suture directly into the cell (evening-primrose, lily). Here the dissepiments come away attached to the middle of the valves.
4, Septifragal (septum, and frango, to break), when the valves separate from the dissepiments which remain still united in the axis (Convolvulus).
551. Porous dehiscence is exemplified in the poppy, where the seeds escape by orifices near the top of the fruit. It is not common.
552. Circumscissile (circumscindo, to cut around), when the top of the ovary opens or falls off like a lid, as in Jeffersonia, henbane, plantain.
553. Carpophore. Some fruits, as the Gerania and Umbeliferae, are furnished with a carpophore, that is, a slender column from the receptacle, prolonged through the axis of the fruit, supporting the carpels.
554. The morphology of the pericarp is exceedingly diversified, but it will suffice the learner at first to acquaint himself with the leading forms only, such as are indicated in the following synopsis and more definitely described afterward.
555. The following is a synopsis of the principal forms of Pericarps.
§ 1. FREE FRUITS (FORMED BY A SINGLE FLOWER).
* Pericarps in-dehiscent,
† With usually but one seed, and
‡ Uniform, or l-coated.
1. Separated from the seed.
2. Inflated, often breaking away.
3. Inseparable from the seed.
4. Invested with a cupule (involucre).
5. Having winged appendages.
Double or triple-coated, fleshy or fibrous.
6. Three-coated. Stone cell entire.
7. Two-coated. Stone cell 2-parted.
8. Drupes aggregated.
† With two or more seeds,
X Immersed in a fleshy or pulpy mass.
9. Rind membranous.
10. Rind leathery, separable.
11. Rind hard, crustaceous.
‡ Inclosed in distinct cells.
* Pericarps dehiscent.
12. Dehiscence circumscissile. seeds ∞ .
† Dehiscence valvular or porous;
‡ Simple or 1-carpeled,
13. Opening by the ventral suture.
14. Opening by both sutures.
15. Legume jointed.
‡ Compound pericarps;
16. Placentae parietal with two cells.
Silicle (shepherd's purse).
17. Placentas parietal only when 1-celled.
18. Capsule with carpophore and elastic styles.
§ 2. CONFLUENT FRUITS (FORMED OF AN INFLORESCENCE).
* With open carpels aggregated into a cone. Strobile (pine).
* With closed carpels aggregated into a mass, as in the fig, mulberry, Osage-orange, pine-apple, etc.
556. The achenium is a small, dry, indehiscent pericarp, free from the one seed which it contains, and tipped with the remains of the style (buttercups, Lithospermum).
557. The double achenium of the Umbeliferae, supported on a carpophore is called cremocarp. The 2-carpeled achenium of the Compositae, usually crowned with a pappus, is called cypsela.
558. The achenia are often mistaken for seeds. In the Labiatae and Bor-rageworts they are associated in fours (372). In Geum, Anemone, etc., they are collected in heads. The rich pulp of the strawberry consists wholly of the overgrown receptacle, which bears the dry achenia on its surface. (440).
432, Achenia of Anemone thalietroides. 433, Cremocarp of Archangelica officinalis, its halves (merocarps) separated and suspended on the carpophore. 434, Cypsela of Thistle with its plumous pappus. 435, Utricle of Chenopodium (pigweed). 436, Caryopsis of Wheat. 437. Samara of Elm. 43S, Glans of Beech. 439, Drupe of Prunus. 440, Fruit of Fragaria Indica, a fleshy torus like the strawberry.
559. The utricle is a small, thin, pericarp fitting loosely upon its one seed, and often opening transversely to discharge it (pigweed, prince's feather).
560. Caryopsis, the grain or fruit of the grasses, is a thin, dry, 1-seeded pericarp, inseparable from the seed.
561. Samara; dry, 1-seeded, indehiscent, furnished with a membranous wing or wings (ash, elm, maple).
562. Glans or nut; hard, dry, indehiscent, commonly 1-seeded by suppression (§ 545), and invested with a persistent involucre called a cupule, either solitary (acorn, hazelnut) or several together (chestnut, beechnut).
563. Drupe, stone-fruit; a 3-coated, 1-celled, indehiscent pericarp, exemplified in the cherry, peach. The outer coat (epidermis) is called the epicarp, the inner is the nucleus or endocarp, hard and stony; the intervening pulp or fleshy coat is the sarcocarp (σaρξ, flesh). These coats are not distinguishable in the ovary.
564. Tryma, a kind of dryish drupe, 2-coated, the epicarp fibro-fleshy (butternut) or woody (hickory), the nucleus bony with its cell often deeply 2-parted (cocoa-nut).