When the fruit is mature and the seeds are ripe, the carpels usually give way either at the ventral or dorsal suture or at both, and so allow the seeds to escape. The fruit in this case is dehiscent. But some fruits are indehiscent, falling to Dehiscence of fruits. the ground entire, and the seeds eventually reaching the soil by their decay. By dehiscence the pericarp becomes divided into different pieces, or valves, the fruit being univalvular, bivalvular or multivalvular, &c., according as there are one, two or many valves. The splitting extends the whole length of the fruit, or is partial, the valves forming teeth at the apex, as in the order Caryophyllaceae (fig. 6). Sometimes the valves are detached only at certain points, and thus dehiscence takes place by pores at the apex, as in poppy (fig. 7), or at the base, as in Campanula. Indehiscent fruits are either dry, as the nut, or fleshy, as the cherry and apple. They are formed of one or several carpels. In the former case they usually contain only a single seed, which may become so incorporated with the pericarp as to appear to be naked, as in the grain of wheat and generally in grasses. In such cases the presence of the remains of style or stigma determines their true nature.
Fig. 8.—Dry dehiscent fruit. The pod (legume) of the Pea; r, the dorsal suture; b, the ventral; c, calyx; s, seeds.
From Vines’ Students’ Text-Book of Botany, by permission of Swan Sonnenschein & Co.
Fig. 9.—(1) Fruit or capsule of Meadow Saffron (Colchicum autumnale), dehiscing along the septa (septicidally); (2) same cut across, showing the three chambers with the seeds attached along the middle line (axile placentation).
Fig. 10.—Diagram to illustrate the septicidal dehiscence in a pentalocular capsule. The loculaments l correspond to the number of the carpels, which separate by splitting through the septa, s.
Fig. 11.—The seed vessel (capsule) of the Flower-de-Luce (Iris), opening in a loculicidal manner. The three valves bear the septa in the centre, and the opening takes place through the back of the loculaments. Each valve is formed by the halves of contiguous carpels.
Fig. 12.—Diagram to illustrate loculicidal dehiscence. The loculaments l, split at the back, and the valves separate, bearing the septa s on their centres.
Fig. 13.—Diagram to illustrate septifragal dehiscence, in which the dehiscence takes place through the back of the loculaments l, and the valves separate from the septa s, which are left attached to the placentas in the centre.