Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/159

Rh DEHI3CEXCE OF FRUITS.] BOTANY 149 a fruit as the Peach or Plum, where they are separable one from the other; in them the epicarp forms what is commonly called the skin ; the mesocarp, much developed, forms the flesh or pulp, and hence has sometimes been called sarcocarp; while the endocarp, hardened by the production of woody cells, forms the stone or putamen, immediately covering the kernel of the seed. The pulpy matter found in the interior of fruits, such as the Gooseberry, Grape, and Catharfcocarpus Fistula, is formed from the placentas, and must not be con founded with the sarcocarp. In some fruits, as in the Nut, the three layers become blended together, and are indistin guishable. In Bladder Senna (Colutea arborescens) the pericarp retains its leaf-like appearance, but in most cases it becomes altered both in consistence and in colour. Thus in the Date the epicarp is the outer brownish skin, the pulpy matter is the mesocarp or sarcocarp, and the thin papery-like lining is the endocarp covering the hard seed. In the Medlar the endocarp becomes of a stony hardness. In the Melon the epicarp and endocarp are very thin, while the mesocarp forms tho bulk of the fruit, differing in texture and taste in its external and internal parts. The rind of the Orange consists of epicarp and mesocarp, while the endocarp forms partitions in the interior, filled with pulpy cells. The part of the pericarp attached to the peduncle is called its base, and the point where the style or stigma existed is the apex. This latter is not always the apparent apex, as in the case of the ovary; it may be lateral or even basilar. The style sometimes remains in a hardened form, rendering the fruit apiculate ; at other times it falls off, leaving only traces of its existence. The presence of the style or stigma serves to distinguish certain single- seeded pericarps from seeds. When the fruit is mature and the contained seeds 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 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 may extend the whole length of the fruit, or it may be only partial, the valves forming teeth at the apex of the fruit, and the dehiscence being opicilar, as in Gary ophyllac ere (fig. 283). Sometimes the valves are detached only at certain points, and thus dehiscence takes place by pores at the apex, as in Poppy (fig. 269), or at the base, as in Campanula. Indehiscent fruits are either dry, as the Nut, or fleshy, as the Cherry and Apple. They may be 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. Such fruits are called pscudospernwus or false- seeded, and are exemplified in the grain of Wheat. In such cases the presence of the style or stigma determines their true nature. Dehiscent fruits, when composed of single carpels, may open by the ventral suture only, as in the Pocony, Hellebore, Aquilegia (fig. 300), and Caltha ; by the dorsal suture only, as in Magnolias and some Protcaceai, or by both together, as in the Pea (fig. 256) and Bean ; in these cases the dehiscence is called sutured. When composed of several united carpels, two types of dehiscence may be recognized a longitudinal type and a transverse type. In the longitudinal type the separation may take place by the dissepiments throughout their length, so that the fruit is resolved into its original carpels, and each valve will be a carpel, as in Rhododendron, Colchicum, &c. This dehiscence, in consequence of taking place through the lamell;c of the septum, is called septicidal (figs. 284, 285). The valves may separate from their commissure, or central line of union, carrying the placentas with them, or they may leave the latter in the centre, so as to form with the Fig. 285. Fig. 287. Fig. 283. Fin. 283. Seed-vessel or capsule of Campion (Lychnis), opening by ten teelh nt the apex. The placenta is free central. The calyx is seen surrounding tho seed-vessel, but not adherent. FIG. 284. Fruit or capsule of Meadow Saffron (Cokhicum autumnale), dehiscing by three valves in a septicidal manner. The fruit is thus resolved into its three component carpels, with their styles and stigmas. FIG. 285. Diagram to illustrate the septicidal dehiscence In a pcntalocular capsule. The loculaments I correspond to tho number of the carpels, which separate by splitting through the septa t. FIG. 286. The seed vessel (capsule) of the Flower-de-Lnce (Iris), opening In a loculicidal manner. The three valves bear the septa in the centre, and tho opening takes place through the back of the loculaments. Each valve is formed by the halves of contiguous carpels. Fio. 287. Diagram to illustrate loculicidal dehlscenco. The loculaments /, split at the back, and the valves separate, bearing the septa s on their centres. FIG. 288. Diagram to illustrate septifragal dehiscence, in which the dehiscence takes place through the back of the loculaments I, and the valves separate from the septa s, which are left attached to the placentas in the centre. axis a column of a cylindrical, conical, or prismatic shape, which is termed the columella. The union betsveen tho edges of the carpels may be persistent, and they may dehisce by the dorsal suture, or through the back of the loculaments, as in the Lily and Iris (figs. 286, 287). In these cases each valve consists of a half of each of two contiguous carpels. The placentas either remain united to the axis, or they separate from it, being attached to the septa on the valves. This dehiscence is loculicidal. When the outer walls of the carpels break off from the septa, leaving them attached to the columella, the dehiscence is said to be septifragal (fig. 288), and where, as in Linum catharticum and Calluna, the splitting takes place first of all in a septicidal manner, the fruit is described as septicidally septifragal ; while in other cases, as in Thorn Apple (Datura Stramonium), where the splitting is at first loculicidal, tho dehiscence is loculicidally septifragal. In all those forms the separation of the valves takes place either from above downwards or from below upwards. But when the splitting only extends for a short distance, then dehiscence takes place by pores, which are situated either at the apex, base, or side, depending on the position of the valves. In the Poppy (fig. 269) the opening takes place by numerous pj a t e pores under the peltate processes bearing the stigmas. In Campanula there are irregular openings towards the middle or base of the pericarp. In Frogsmouth or Snapdragon tho pericarp gives way at certain fixed points, forming two or three orifices, one of which corresponds to the upper carpel, and the other to the lower. These orifices have a ragged appearance at the margins, which has given rise to the term rupturing, sometimes applied to this mode of