Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/136

Rh 126 BOTANY [REPRODUCTIVE ORGANS. G-5-chotomous 2. Biparous Cyme (Dichotomous), including G-5-cho1 Cymes (Dicliasium, Cymose Umbel, Anthela). Elongated form, Ccraslium, Stellaria. b. Contracted form (Verticillaster), Dead-nettle, Pelargo nium. 3. Compound Definite Inflorescence. Strcptocarpus polyan thus, many Calceolarias. C. Mixed Inflorescence. 1; Raceme of Scorpioid Cymes, II or sc- chestnut. 2 Scorpioid Cyme of Capitula, Vernonia ccntrijlora. 3. Compound Umbel of Dichotomous Cymes, Laurustinus. 4. Capitulum of contracted Scorpioid Cymes (Glomerulus), Sea-pink. Tho Mower.&quot; The flower is the tout ensemble of those organs which are concerned in reproduction. It is constituted by a portion ! of the floral axis bearing the sexual organs, usually with 1 certain protective envelopes. The parts borne on the floral axis and composing the flower are all metamorphosed leaves, and, though usually very different in appearance from foliage leaves, their morphological resemblance is frequently shown by their developing as foliage leaves. The axis bearing the parts of the flower is usually very much contracted, no internodes being developed, and it frequently expands into a flattened or hollowed expansion termed the thalamus or torus; at other times, though rarely, the internodes are developed and it is elongated. Upon this torus the parts of the flower are arranged in a crowded manner, usually forming a series of verticils, the parts of which alternate; but they are sometimes arranged in a spiral manner, especially if the floral axis be elongated. In a typical flower, as in fig. 172, we recognize four distinct whorls of leaves : an outer whorl of five parts, the calyx ; within it, another whorl of five parts alternating with those of the outer whorl, the corolla ; next comes a whorl of parts alternating with the parts of the corolla, the androecium ; and in the centre is the gyncedum. Fig 1 73 is a diagrammatic representation of the arrangement of the parts of such a flower. The flower is supposed to be cut transversely, and the parts of each whorl are distinguished by a different symbol. Of these whorls the two internal, forming the male and female sexual organs, constitute the essential organs of reproduction ; the two outer whorls are the protective coverings or floral envelopes. The calyx or outer covering (fig. 172, c) is formed of leaves, called sepals, which are generally of a greenish colour. The corolla p, the next covering, is composed of leaves, called petals, which are often showy, and normally alternate with the sepals. Sometimes, as in many Monocotyledons, the calyx and corolla both display rich colouring, and are apt to be con founded. In such cases the term perianth, or perigone, has been applied to avoid ambiguity. Thus, in the Tulip, Crocus, Lily, Hyacinth, authors speak of the parts of the perianth, in place of calyx and corolla, although in these plants an outer whorl (calyx) may be detected, of three parts, and an inner (corolla), of a similar number, alternat ing with them. When the parts of the calyx are in appear ance like petals they are said to )Qpetaloid, as in Liliaceta In some cases the petals have the appearance of sepals, then they are sepaloid, as in Juncacese. The term perianth is usually confined to the flowers of Monocoty ledons, whatever colour they present, whether green, as in Asparagus, or coloured, as in Tulip. Some use the term perianth as a general one, and restrict the use of perigone to cases where a pistil only is present. In plants, as Nymphsea alba, where a spiral arrangement of the floral leaves occur, it is not easy to say where tha calyx ends and the corolla begins, as these two whorls pass insensibly into each other. When both calyx and corolla are present, the plants are dichlamydeous ; occasionally one becomes abortive, and then the flower is monochlamydeous (fig. 174), having a calyx only, or apdalous, having no petals. At times both arc abortive, and then the flower is aclda- mydeous, or naked. It is important to remember that it only one perianth-whorl is present it is the calyx. The outermost whorl of the essential organs, collectively termed the audrcecium, is composed of a series of leaves 175. Fig. 174. Fig. 176. FIG. 172. Flower of Crassula rubens. c, c, sepals; /&amp;gt;, p, petals; e, e, stamens; o, o, carpels, each of them having a small scale-like appendage at the base. FIG. 173. Diagram of a completely symmetrical flower, consisting of four whorls, each consisting of five parts. The outer row is the calyx formed of rive sepals ; the second is the corolla of five petals, alternating with the sepals; the third is the andrcecium, consisting of five stamens, alternating with the petals; the central whorl is the gynoccium, consisting of five carpels, alternating with the stamens. FIG. 174. Monochlamydeous (apetalous) flower of Goosefoot (Chenopodimri), con sisting of a single perianth (calyx) of five parts, enclosing five stamens, which are opposite the divisions of the perianth, owing to the absence of the petals. FIG. 175. Stamen, consisting of a filament (stalk) /and an anther a, containing powdery matter p, denominated pollen, which is discharged through slits iu the two lobes of the anther. FIG. 176. The pistil of Tobacco (Nicotiana Tatacitm), consisting of the ovary o, containing ovules, the style s, and the capitate stigma g. The pistil is placed on the receptacle r, at the extremity of the peduncle. distinguished as the staminal leaves or stamens. These are the male sexual organs. In their most differentiated form each consists of a stalk, either filiform or foliaceous, the filament (fig. 175, /) supporting at its summit a lobed saccate mass, the anther (fig. 175, a), which contains a powdery matter, the pollen (fig. 175,^&amp;gt;), which is discharged therefrom. In many cases, however, the staminal leaf resembles more nearly a cataphyllary leaf, bearing the pollen- sacs scattered over its surface, as in Cycadaceae. The Plate X gynoscium or pistil is the central portion of the flower, and is the female sexual organ. It consists of one or more folded leaves, called carpels, either separate (fig. 172, c) or combined (fig. 174.) The parts distinguished in the pistil are the ovary (fig. 17G, o), which is the lower portion en closing the ovules destined to become seeds, and the stigma (fig. 176, &amp;lt;/), a portion of loose cellular tissue uncovered by epidermis, which is either sessile on the apex of the ovary, as in the Poppy, or is separated from it by a prolonged Plate 1. portion called the style (fig. 17G, s). The androecium and gyncecium are not present in all flowers. When both are present the flower is hermaphrodite ; and in descriptive botany such a flower is indicated by the symbol $? . When