=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_). [Illustration: Fig. 475. Diagrams illustrating three types (in cross-section) of the dehiscence of dry fruits. _Loc_, loculicidal; _Sep_, Septicidal, Septifragal.] [Illustration: Fig. 476. Fruit of sweet pea; a pod.] =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.