Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/146

136 BOTANY [KEI HODUCTIVE ORGANS. filament (fig. 175, /), and a broader portion, usually of two "lobes, termed the anther (fig. 175, a), containing a powdery matter, called pollen (/>), and supported upon the end of the filament. That portion of the filament in contact with the anther lobes is termed the connective. The exact morphological relations of these parts is not definitely settled. Some consider the filament as representing the petiole, and the anther as being the folded lamina ; others again regard the connective as representing the lamina, the rest of the filament being the petiole, and the anther lobes as mere appendages of the lamina. The filament is no more essential to the stamen than the petiole is to the leaf, or the claw to the petal. If the anther is absent the stamen is abortive, and cannot perform its functions. The anther is developed before the filament, and when the latter is not produced, the anther is sessile, or has no stalk, as in the Mistleto. Tlie fila- The filament, when structurally considered, is found to ment. consist of a thin epidermis, on which occasionally stomata and hairs occur, and a layer of cellular tissue enclosing a bundle of spiral vessels, which traverses its whole length, and terminates at the junction between the filament and the anther. The filaments of Callitriche verna are said to have no vessels. The filament is usually, as its name imports, filiform or thread-like, cylindrical, or slightly tapering towards its summit. It is often, however, thickened, compressed, and flattened in various ways, becoming pdaloid in Canna, Maranta, Nympha?a alba (fig. 179) ; subulate or slightly broadened at the base, and drawn out into a point like an awl, as in Butomus umbellatus ; davate, that is, narrow below and broad above, as in Thalictrum. In some instances, as in Tamarix gallica, Peganum Harmala, and Campanula, the base of the filament is much dilated, and ends suddenly in a narrow thread-like portion. In these cases the base may represent the sheath or vagina of the leaf, and may give off stipulary processes in a lateral direction, as in Allium and Alyssum calycinurn. The filament varies much in length and in firmness. The length sometimes bears a relation to that of the pistil, and to the position of the flower, whether erect or drooping. The filament is usually of sufficient solidity to support the anther in an erect position ; but sometimes, as in Grasses, it is very delicate and capillary, or hair-like, so that the anther is pendulous (fig. 212, s). The filament is generally continuous from one end to the other, but in some cases it is bent or jointed, becoming yeniculate ; at other times, as in the Pellitory, it is spiral. It is frequently colourless ; but, in many instances, it exhibits different colours. In Fuchsia and Poinciana, it is red ; in Adamia and Tradescantia virginica, blue ; in CEnothera and Ranunculus acris, yellov. Hairs, scales, teeth, or processes of different kinds are sometimes developed on the filament. In Tradescantia virginica, or Spiderwort, the hairs are beautifully coloured, moniliform or necklace-like, and rotation is seen in them (p. 84). Such a filament is bearded oi stupose. At the base of the filament glandular or scaly appendages are occasion ally produced, either on its internal or its external surface. These may be either parts of a whorl, to be aftenvards noticed under the name of the disk, or separate prolonga tions from the filament itself, which is hence called appendiculate, or sometimes strumose. Filaments are usually articulated to the thalamus or torus, and the stamens fall off after fertilization ; but in Campanula and some other plants they are continuous with the torus, and the stamens remain persistent, although in a withered state. Changes are produced in the whorl of stamens by cohesion of the filaments to a greater or less extent, while the anthers remain free ; thus, all the filaments of the andrcecium may unite, forming a tube round the pistil, or a central bundle when the pistil is abortive, the stamens becoming mon- adelphous, as occurs in plants of the Mallow tribe; or Plate III. they may be arranged in two bundles, the stamens being diadelphoiis, as in Polygala, Fumaria, and Pea; in this case the bundles may be equal or unequal. It frequently happens, especially in Papilionaceous flowers, that out of ten stamens nine are united by their filaments, while one (the posterior one) is free (fig. 218). When there are three or more bundles the stamens arc triadelphous, as in Hypericum a^gyptiacum, or polyadelphous, as in Luhea paniculata and Ricinus communis. In some cases, especially in the Mallov tribe, the stamens cohere, having been originally separate, but in most other cases each bundle is produced by the branching of a single stamen. When there are three stamens in a bundle we may conceive the lateral ones as of a stipulary nature. In Lauraceo} there are perfect stamens, each having at the base of the filament two abortive stamens or staminodes, which may be analogous to stipules. Filaments sometimes are adherent to the pistil, forming a columna or column, as in Stylidium, Asclepiadacece, llafflesia, Orchidacerc, and Aristolochiacese (fig. 217). The column is called yynostemium, and the flowers are denominated gynandrons. The anther consists of lobes containing minute powdery The anthei matter, called pollen, which, when mature, is discharged by a fissure or opening of some sort. The anther lobes are considered by some as formed by the two halves of the lamina, their back corresponding to the under surface, and their face to the upper surface, united by the midrib, the pollen being the cellular tissue, and the fissure of the anther taking place at the margin, which, however, is often turned towards the face. In this view, the two cavities which are found to exist in each lobe may correspond with the upper and under layer of cells, separated by a septum equivalent to the fibre-vascular layer of the leaf. Others view the anther as formed by each half of the lamina being folded upon itself, so that the outer surface of both face and back corresponds to the lower side of the leaf, and the septum dividing each cavity into two is formed by the united upper surfaces of the folded half. Again, others hold that the connective represents the lamina of the leaf to which the anther lobes are mere appendages. There is a double covering of the anther the outer, or exothccium, resembles the epidermis, and often presents stomata and projections of different kinds (fig. 219); the inner, or cndotheciuw, is /t Fig. 218. Fig. 219. Fig. 220. FIG. 218. Stamens and pistil of Sweet Pea (Lathyrut). The stamens are dia- dclphous, nine of them being united by their filaments/, while one of them, c, is free; the upper part of the pistil is marked st, the calyx, c. FIG. 219. Broken-down fibrous cells cf of the endothccium of the anther of the Melon. The walls of the cells are absorbed, and the fibres are set free. The exotliecium or outer epidermis is marked ce. FIG. 220. Quadrilocular or tetrathccal anther of the flowering Rush (Bvtomut umbellatus). The anther entire, a, with its filament; section of anther, 6, showing the four loculi. formed by a layer or layers of cellular tissue (fig. 219, cf), the cells of which have a spiral, annular, or reticulated fibre

in their interior. This internal lining varies in thickness,