Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/160

Rh 150 T A N Y [REPRODUCTIVE ORGANS. dcluscenco. In Saxifraga a splitting for a short distance of the ventral sutures of the carpels takes place, so that a single large apical pore is formed. In Caryophyllacere (fig. 283) numerous small valvular splittings occur, forming teeth at the apex, and a single apical orifice is formed. In the fruit of Cruciferse, as Wallflower, there is a form of longitudinal dehiscence (fig. 289) in which the valves separate from the base of the fruit, leaving a central replum, or frame, which is a phragma formed by a prolongation from the parietal placentas on opposite sides of the fruit, extending between the ventral sutures of the carpels. In Orchidaceio (fig. 290) the pericarp, when ripe, separates into three valves, in a loculicidal manner, but the midribs of the carpels, to which the placentas are attached, remain adherent to the axis both at the apex and base, and form three arches, bearing the seeds, after the valves have fallen. In fruits with a free central placenta it is sometimes difficult to tell whether the dehiscence is septicidal or loculicidal, inasmuch as there are no dissepiments, and the placentas and seeds form a column in the axis. Their number, as well as alternation or opposition, as compared with the sepals, will aid in determining whether the valves are the entire carpellary leaves, as in septicidal dehiscence, or only half carpels united, as in loculicidal dehiscence. The other type of dehiscence is transverse, the dehiscence in this case being called circumscissile. In this dehiscence the upper part of the united carpels falls off in the form of a lid or operculum, as in Anagallis and in Henbane (Hyoscyamus) (fig. 291), and hence the fruit is often denominated operculatc. In such instances we may either suppose that the fruit or seed-vessel is formed by a number of articulated leaves like those of the Orange, the division taking place where the lamina? join the petioles, or that the receptacle is prolonged in the form of a hollow cup, and the lid represents leaves united to it by articulation. i - 289. Fig. 292. FIG. 289. Siliqua or seed-vessel of Wallflower (Cheiranthus Cheiri), opening by two valves, which separate from the base upwards, leaving the seeds attached to the placentas in the middle, with a replum between. I- IG. 200 Seed-vessel of an Orchid (Orchis), opening by three valves v v v, which r the placentas and seeds in their middle. The midribs of the carpels remain united at the base and apex, and the withered floral envelopes e are Keen attached at the apex. FIG. 2!)1. Seed-vessel of Henbane (Ilyoicyamus niger), opening by circum- ehiscence. The upper part of the seed-vessel comes off in the form of a lid, nnd the capsule has been on this account called pyxis or pyxidium. no. JJA- Ihe fruit of the Fennel (Fccniculum vulgare), arrived at maturity. It s into two cocci or achamia, each of which is marked with obtuse prominent ridges on the surface, and is suspended from the summit of a process of he axis (columclla), called a carpophore. Ho 293. Lomentum or lomentaceous legume of. a species of Sainfoin tysarum). Each seed is contained in a separate cavity by the folding Js of the walls of the legume at equal intervals; nnd the legume, when ipe, separates transverely into single-seeded portions or mcricarps. Sometimes the axis is prolonged beyond the base of the Plate III. carpels, as in the Mallow and Castor-oil plant, the carpels being united to it throughout their length by their aces, and separating from it without opening. In the Umbelliferno the two carpels separate from the lower part of the axis, and remain attached by their apices to a prolongation of it, called a carpophore or podocarp, which splits into two (fig. 292) and suspends them ; hence the name cremocarp is applied to this fruit, which divides into two suspended mericarps. The general term scluzocarp is applied to all dry fruits, which break, up into two or more one-seeded indehiscent mericarps, as in Hedysarum (fig. 293). In Geraiiiacese the axis is prolonged beyond the carpels, forming a carpophore,- to which the styles are attached, and the pericarps separate from below upwards, before dehiscing by their ventral suture (fig. 152). Carpels which separate one from another in this manner ara called cocci. They are well seen in Euphorbiaceae, where there are Plato X I f 1 usually three such carpels, and the fruit is designated & ? tricoccous. In many of them, as Hura crepitans, the cocci separate with great force and elasticity, the cells being called dissilient. In many Leguminous plants, such as Ornithopus, Hedysarum (fig. 293),Entada, Coronilla, and the Gum-arabic plant (Acacia arabica), the fruit becomes a schizocarp by the formation of transverse partitions from the folding in of the sides of the pericarp, and distinct separations taking place at these partitions by what has been termed solubility. In Cathartocarpus Fistula the schizocarp exhibits no evident depressions externally. Some look upon these pods as formed by pinnate leaves folded, and the divisions as indicating the points where the different pairs of pinnae are united. Fruits may be formed by one flower, or they may be the product of several flowers combined. In the former case they are either apocarpous, of one mature carpel or of several separate free carpels ; or syncarpous, of several carpels, more or less completely united. These different kinds of fruits may be indehiscent or dehiscent. When the fruit is composed of the ovaries of several flowers united, it is usual to find the bracts and floral envelopes also joined with them, so as to form one mass ; hence such fruits are called multiple, confluent, or anthocarpous. The term simple is perhaps properly applied to fruits which are formed by the ovary of a single flower, whether they are composed of one or several carpels, and whether these carpels are separate or Fig. 295. Fig. 296. FIG. 294. Fruit of a species of Dock (nitmex), cut vertically. It Is a mono- spermous indehiscent diy fruit, called an achene, or achfcnium. The outer part, ov, is the pericarp or seed-vessel containing the seed, with its coverings The seed contains nourishing matter, called albumen or perispcrm alb, and the embryo plant pi, with its cotyledons pointing downwards, and its radicle upwards. The seed is orthotropal, and the embryo is inverted. At the upper part of the pericarp two of the styles and stigmas arc seen curving dowmvaids. At the base part of the perianth is represented. FIG. 295. Achsenium of Crowfoot (lianunatltis). A single-seeded seed-vessel, with the pericarp applied closely to the seed. Such fruits resemble seed in appearance ; the style nnd stigma s aid in distinguishing them. FIG. 296. Seed-vessel of Acer J seudo-platanus (Sycamore, called Plane in Scot land), composed of two samaras or winged monospcrmous carpels united; a, upper part forming a dorsal wing; I, lower portion corresponding to the loculamcnts. combined. Simple fruits are hence sometimes denominated monogyncecial, as being formed by one gyncccium ; while multiple fruits are called polygynoecial, as being formed by many gyncecia.