Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/168

Rh 158 BOTANY [REPRODUCTIVE ORGANS and is termed a nucule (fig. 240, n}. This consists of a large central cell, of which the contents a t the apex are clear and hyaline, while the lower part contains much starch and fat. Rising from its base and twisting round it are five long tubes (fig. 328), at the extremity of each of which C Fig. 327. Fio. 327. Archegonium of the Forked Spleenwort (Asp .enium septentrionale) Immediately after fertilization, a, canal lending to the large cell (oosphere) e at the base of the archegonium ; e, nucleated embryonic cell, whence the sporan- giforous frond proceeds. Fio. 328. Nucule of Chara entire, with five cells, wound round a large central cell in a spiral manner; a, crown or coronula of five smaller cells. Fio. 329. Pistillidium of Llvenvort (Marchantia). It is a cellular body surrounded by an Involucre (pcrlgone or calyx) b, and septate filaments (paraphyses), and it is provided with a styloid calyptra a. above the apex of the central cell is a single short cell in Chara, while in Nitella it is divided transversely into two. These five or ten short cells form the crown. They unite together so that their apices project as small teeth. Between the crown and the apex of the central cell, which is termed the apical papilla, a cavity is included, bounded at the sides by the five enveloping tubes, which at this point form the neck of the nucule. The cavity of the neck is constricted in the middle by the projection inwards of the tubes to form a sort of diaphragm, so that the enclosed cavity has a rude hour-glass-like shape, the upper cavity closed above by the crown being connected by a narrow canal with a lower cavity bounded beneath by the apical papilla of the central cell. When fertilization takes place slits are formed betwixt the five tubes of the neck, beneath the crown and above the diaphragm. The antherozoids from the globule enter by them into the upper cavity, pass through the canal into the lower one, and fuse with the apical papilla of the central cell or oosphere. The oospore thus formed becomes detached from the plant, being covered by the thickened inner wall of the tube which invested it. The nucule rises from the base of one of the whorl leaves in Chara, and is therefore above the globule ; in Nitella it is produced upon the leafy axis beneath the globule. In Mosses In Mosses the archegonia are frequently situated along and Hepa- w jth the antheridia and paraphyses. They are surrounded by the same whorl of leaves, or perichcetium, when the moss is said to be hermaphrodite, or they occur separately on the same OP on different plants, the moss being then monoecious or dioecious. The term periyone is applied to the whorl of leaves around the antheridia. The basal portion of the archegonia which surrounds the oosphere is termed the epigone. In Hepaticoj the archegonia (fig. 329) are situ ated in the substance of the thallus itself, or they may be in various situations, as in Jungermannia (fig. 330); in Marchantia they are produced upon the under surface of a stalked stellate disk (fig. 331). In Thallo- In many Thallogens no structure analogous to a female gens. organ has been as yet discovered ; in some, however, such structures have been met with. Thus amongst Algtc large cells, termed oogonia, are found, in which usually one, sometimes many (Fucaceae), oospheres are produced (fig. 332). The antherozoids from the antheridium fertilize these, penetrating the oogonia at a definite point thinner than the surrounding portion ; and oospores are formed. In the Floridere, a group of Alga;, the organs are different in character. Here the antherozoids are not motile, having no cilia. On discharge from the antheridium, these are washed into a long filiform hollow body, termed the tricliogynium. This is supported usually upon a cellular stalk the trichophorc at the side of the base of which is a small cellular mass. The antherozoids having entered the tricliogynium, fertilization is effected, and results in the formation, from the cellular mass at the base of the Fig. 331. Fio. 330. Archegonia of Jungermannia bicuspiJata. a, archegonium, with a tulic leading to a cavity near the base of which is a cell; 6, archegonium afterfeitil- ization, with the cell c divided Into two nucleated portions. This double nu cleated body is the rudiment of the fruit-bearing stalk. At the apex of the canal leading to the cell are seen spermatozoids * s. FIG. 331. Thullus of Liverwort (Marchantia polymorpha), bearing a stalked fruit 3, which is the product of the impregnated cell of the archegonium. The receptacle at tbe apex of the stalk bears on its under surface sporangia con taining spores and elaters. The spores, when germinating, produce a tluillus, on which antheridia and archegonia are formed. trichophore, of a large cell, the cystocarp, in which spores are formed. In the Saprolegnieo} the antheridia actually penetrate into the oogonium and discharge their anthero zoids. Amongst Fungi it is rare to find sexual organs. In some thecasporous fungi, as Eurotium, a sexual pro cess has been observed. The female organ, here termed ascogonium or carpoyonium, is of a spiral elongated char acter, immediately surrounding which are the antheridia, Pi-. 332. Fio. 302. Transverse section of a conceptacle of a Seaweed (Fucus vesiculosus) , showing the spores in the coverings, p, and paraphyses lining the cavity. This spores escape by nn orifice o. few in number, which open into the apex of the female organ, and discharge their antherozoids. The result is the formation of cellular tissue round the ascogonium, forming what is termed a perithecium, and within the ascogonium large cells (asci) are produced, in which spores