In species with smaller and less conspicuous flowers, such as G. molle, the flowers of which are only 1⁄3 to ½ in. in diameter, self-pollination is rendered possible, since the divisions of the stigma begin to separate before the outer stamens have 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 rolling elastically outwards and upwards or becoming spirally 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 distribution of which is favoured by the presence of bristles or hairs. The embryo generally fills the seed, and the cotyledons are rolled or folded on each other.
Geranium is the most widely distributed genus; it has 160 species and is spread over all temperate regions with a few species in the tropics. Three British species—G. sylvaticum, G. pratense and G. Robertianum (herb-Robert)—reach the arctic zone, while G. patagonicum and G. magellanicum are found in the antarctic. Erodium contains 50 species (three are British), most of which are confined to the Mediterranean region and west Asia, though others occur in America, in South Africa and West Australia. Pelargonium, with 175 species, has its centre in South Africa; the well-known garden and greenhouse “geraniums” are species of Pelargonium (see [Geranium]).
GERANIUM, the name of a genus of plants, which is taken by botanists as the type of the natural order Geraniaceae. The name, as a scientific appellation, has a much more restricted application than when taken in its popular sense. Formerly the genus Geranium was almost conterminous with the order Geraniaceae. Then as now the geranium was very popular as a garden plant, and the species included in the original genus became widely known under that name, which has more or less clung to them ever since, in spite of scientific changes which have removed the large number of them to the genus Pelargonium. This result has been probably brought about in some degree by an error of the nurserymen, who seem in many cases to have acted on the conclusion that the group commonly known as Scarlet Geraniums were really geraniums and not pelargoniums, and were in consequence inserted under the former name in their trade catalogues. In fact it may be said that, from a popular point of view, the pelargoniums of the botanist are still better known as geraniums than are the geraniums themselves, but the term “zonal Pelargonium” is gradually making its way amongst the masses.
The species of Geranium consist mostly of herbs, of annual or perennial duration, dispersed throughout the temperate regions of the world. They number about 160, and bear a considerable family resemblance. The leaves are for the most part palmately-lobed, and the flowers are regular, consisting of five sepals, five imbricating petals, alternating with five glandules at their base, ten stamens and a beaked ovary. Eleven species are natives of the British Isles and are popularly known as crane’s-bill. G. Robertianum is herb-Robert, a common plant in hedgebanks. G. sanguineum, with flowers a deep rose colour, is often grown in borders, as are also the double-flowered varieties of G. pratense. Many others of exotic origin form handsome border plants in our gardens of hardy perennials; amongst these G. armenum, G. Endressi, G. ibericum and its variety platypetalum are conspicuous.
From these regular-flowered herbs, with which they had been mixed up by the earlier botanists, the French botanist L’Heritier in 1787 separated those plants which have since borne the name of Pelargonium, and which, though agreeing with them in certain points of structure, differ in others which are admitted to be of generic value. One obvious distinction of Pelargonium is that the flowers are irregular, the two petals which stand uppermost being different—larger, smaller or differently marked—from the other three, which latter are occasionally wanting. This difference of irregularity the modern florist has done very much to annul, for the increased size given to the flowers by high breeding has usually been accompanied by the enlargement of the smaller petals, so that a very near approach to regularity has been in some cases attained. Another well-marked difference, however, remains in Pelargonium: the back or dorsal sepal has a hollow spur, which spur is adnate, i.e. joined for its whole length with the flower-stalk; while in Geranium there is no spur. This peculiarity is best seen by cutting clean through the flower-stalk just behind the flower, when in Pelargonium there will be seen the hollow tube of the spur, which in the case of Geranium will not be found, but the stalk will appear as a solid mass. There are other characters which support those already pointed out, such as the absence of the glandules, and the declination of the stamens; but the features already described offer the most ready and obvious distinctions.
To recapitulate, the geraniums properly so-called are regular-flowered herbs with the flower-stalks solid, while many geraniums falsely so-called in popular language are really pelargoniums, and may be distinguished by their irregular flowers and hollow flower-stalks. In a great majority of cases too, the pelargoniums so commonly met with in greenhouses and summer parterres are of shrubby or sub-shrubby habit.
The various races of pelargoniums have sprung from the intermixture of some of the species obtained from the Cape. The older show-flowered varieties have been gradually acquired through a long series of years. The fancy varieties, as well as the French spotted varieties and the market type, have been evolved from them. The zonal or bedding race, on the other hand, has been more recently perfected; they are supposed to have arisen from hybrids between Pelargonium inquinans and P. zonale. In all the sections the varieties are of a highly ornamental character, but for general cultivation the market type is preferable for indoor purposes, while the zonals are effective either in the greenhouse or flower garden. Some of the Cape species are still in cultivation—the leaves of many of them being beautifully subdivided, almost fern-like in character, and some of them are deliciously scented; P. quercifolium is the oak-leaf geranium. The ivy-leaf geranium, derived from P. peltatum, has given rise to an important class of both double- and single-flowered forms adapted especially for pot culture, hanging baskets, window boxes and the greenhouse. Of late years the ivy-leaf “geraniums” have been crossed with the “zonals,” and a new race is being gradually evolved from these two distinct groups.