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GERANIACEAE
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GERANIACEAE , in See also:botany, a small but very widely distributed natural See also:order of See also:Dicotyledons belonging to the subclass Polypetalae, containing about 36o See also:species in 11 genera. It is re-presented in See also:Britain by two genera, See also:Geranium (See also:crane's-See also:bill) and Erodium (See also:stork's-bill), to which belong nearly two-thirds of the See also:total number of species. The See also:plants are mostly herbs, rarely becoming shrubby, with generally See also:simple glandular hairs on the See also:stem and leaves. The opposite or alternate leaves have a pair of small stipules at the See also:base of the stalk and a palminerved blade. The See also:flowers, which are generally arranged in a cymose inflorescence, are hermaphrodite, hypogynous, and, except in Pelargonium, See also:regular. The parts are arranged in See also:fives. There are five See also:free sepals, overlapping in the bud, and, alternating with these, five free petals. In Pelargonium the See also:flower is zygomorphic , with a spurred posterior sepal and the petals differing in See also:size or shape. In Geranium the stamens are obdiplostemonous, i.e. an See also:outer whorl of five opposite the petals alternates with an inner whorl of five opposite the sepals; at the base of each of the antisepalous stamens is a See also:honey-gland. In Erodium the members of the outer whorl are reduced to See also:scale-like structures (staminodes), and in Pelargonium from two to seven only are fertile. There is no satisfactory explanation of this break inthe regular See also:alternation of successive whorls; the outer whorl of stamens arises in course of development before the inner, so that there is no question of subsequent displacement. There are five, or sometimes fewer, carpels, which unite to See also:form an ovary with as many See also:chambers, in each of which are one or two, rarely more, pendulous anatropous ovules, attached to the central See also:column in such a way that the micropyle points outwards and the raphe is turned towards the See also:placenta. The See also:long See also:beak-like See also:style divides at the See also:top into a corresponding number of slender stigmas. The larger-flowered species of Geranium are markedly protandrous, the outer stamens, inner stamens and stigmas becoming functional in See also:succession. For instance, in meadow crane's-bill G. pratense, each whorl of stamens ripens in turn, becoming erect and shedding their See also:pollen; as the anthers See also:wither the filaments See also:bend outwards, and when all the anthers have diverged the stigmas become mature and ready for See also:pollination. By this Meadow Crane's-bill, Geranium pratense. See also:Flora Londinensis.) 1, Flower after removal of petals. 3, Floral See also:diagram, the dots 2, See also:Fruit after splitting. 1 and 2 opposite the inner stamens about natural size. represent honey-glands. arrangement self-pollination is prevented and See also:cross-pollination ensured by the visits of bees which come for the honey secreted by the glands at the base of the inner stamens. In species with smaller and less conspicuous flowers, such as G. molle, the flowers of which are only a to % in. in See also:diameter, self-pollination is rendered possible, since the divisions of the stigma begin to See also:separate before the outer stamens have See also:shed all their pollen; the nearness of the stigmas to the dehiscing anthers favours self-pollination. In the ripe• fruit ,the carpels separate into five one-seeded portions (cocci), which break away from the central column, either See also:rolling elastically outwards and upwards or becoming spirally See also:twisted. In most species of Geranium the cocci split open on the inside and the seeds are shot out by the elastic uptwisting (fig. 1); in Erodium and Pelargonium each coccus remains closed, and the long twisted upper portion separates from the central column, forming an awn, the See also:distribution of which is favoured by the presence of bristles or hairs. The embryo generally fills the See also:seed, and the cotyledons are rolled or folded on each other. (After See also:Curtis, Geranium is the most widely distributed genus; it has 16o species and is spread over all temperate regions with a few species in the tropics. Three See also:British species—G. sylvaticum, G. pratense and G. Robertianum (See also:herb-See also:Robert)—reach the See also:arctic See also:zone, while G. patagonicum and G. magellanicum are found in the See also:antarctic. Erodium contains 50 species (three are British), most of which are confined to the Mediterranean region and See also:west See also:Asia, though others occur in See also:America, in See also:South See also:Africa and West See also:Australia. Pelargonium, with 195 species, has its centre in South Africa; the well-known See also:garden and See also:green-See also:house " geraniums " are species of Pelargonium (see GERANIUM). Additional information and CommentsThere are no comments yet for this article.
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