1911 Encyclopædia Britannica/Iris (plant)

IRIS, in botany. The iris flower belongs to the natural order Iridaceae of the class Monocotyledons, which is characterized by a petaloid six-parted perianth, an inferior ovary and only three stamens (the outer series), being thus distinguished from the Amaryllidaceae family, which has six stamens. They are handsome showy-flowered plants, the Greek name having been applied on account of the hues of the flowers. The genus contains about 170 species widely distributed throughout the north temperate zone. Two of the species are British. I. Pseudacorus, the yellow flag or iris, is common in Britain on river-banks, and in marshes and ditches. It is called the “water-flag” or “bastard floure de-luce” by Gerard, who remarks that “although it be a water plant of nature, yet being planted in gardens it prospereth well.” Its flowers appear in June and July, and are of a golden-yellow colour. The leaves are from 2 to 4 ft. long, and half an inch to an inch broad. Towards the latter part of the year they are eaten by cattle. The seeds are numerous and pale-brown; they have been recommended when roasted as a substitute for coffee, of which, however, they have not the properties. The astringent rhizome has diuretic, purgative and emetic properties, and may, it is said, be used for dyeing black, and in the place of galls for ink-making. The other British species, I. foetidissima, the fetid iris, gladdon or roast-beef plant, the Xyris or stinking gladdon of Gerard, is a native of England south of Durham, and also of Ireland, southern Europe and North Africa. Its flowers are usually of a dull, leaden-blue colour; the capsules, which remain attached to the plant throughout the winter, are 2 to 3 in. long; and the seeds scarlet. When bruised this species emits a peculiar and disagreeable odour.

Iris florentina, with white or pale-blue flowers, is a native of the south of Europe, and is the source of the violet-scented orris root used in perfumery. Iris versicolor, or blue flag, is indigenous to North America, and yields “iridin,” a powerful hepatic stimulant. Iris germanica of central Europe, “the most common purple Fleur de Luce” of Ray, is the large common blue iris of gardens, the bearded iris or fleur de luce and probably the Illyrian iris of the ancients. From the flowers of Iris florentina a pigment—the “verdelis,” “vert d’iris,” or iris-green, formerly used by miniature painters—was prepared by maceration, the fluid being left to putrefy, when chalk or alum was added. The garden plants known as the Spanish iris and the English iris are both of Spanish origin, and have very showy flowers. Along with some other species, as I. reticulata and I. persica, both of which are fragrant, they form great favourites with florists. All these just mentioned differ from those formerly named in the nature of the underground stem, which forms a bulb and not a strict creeping rhizome as in I. Pseudacorus, germanica, florentina, &c. Some botanists separate these bulbous irises from the genus Iris, and place them apart in the genus Xiphium, the Spanish iris, including about 30 species, all from the Mediterranean region and the East.

Fig. 1.—Gynoecium of Iris, consisting of an inferior ovary o, and a style, with three petaloid segments s, bearing stigmas st.

Fig. 2.—Diagram of Trimerous Symmetrical Flower of Iris, with two whorls of perianth, three stamens in one whorl and an ovary formed of three carpels. The three dots indicate the position of an inner whorl of stamens which is present in the allied families Amaryllidaceae and Liliaceae but absent in Iridaceae.

The iris flower is of special interest as an example of the relation between the shape of the flower and the position of the pollen-receiving and stigmatic surfaces on the one hand and the visits of insects on the other. The large outer petals form a landing-stage for a flying insect which in probing the perianth-tube for honey will first come in contact with the stigmatic surface which is borne on the outer face of a shelf-like transverse projection on the under side of the petaloid style-arm. The anther, which opens towards the outside, is sheltered beneath the over-arching style arm below the stigma, so that the insect comes in contact with its pollen-covered surface only after passing the stigma, while in backing out of the flower it will come in contact only with the non-receptive lower face of the stigma. Thus an insect bearing pollen from one flower will in entering a second deposit the pollen on the stigma, while in backing out of a flower the pollen which it bears will not be rubbed off on the stigma of the same flower.

The hardier bulbous irises, including the Spanish iris (I. Xiphium) and the English iris (I. xiphioides, so called, which is also of Spanish origin), require to be planted in thoroughly drained beds in very light open soil, moderately enriched, and should have a rather sheltered position. Both these present a long series of beautiful varieties of the most diverse colours, flowering in May, June and July, the smaller Spanish iris being the earlier of the two. There are many other smaller species of bulbous iris. Being liable to perish from excess of moisture, they should have a well-drained bed of good but porous soil made up for them, in some sunny spot, and in winter should be protected by a 6-in. covering of half-decayed leaves or fresh coco-fibre refuse. To this set belong I. persica, reticulata, filifolia, Histrio, juncea, Danfordiae Rosenbachiana and others which flower as early as February and March.

The flag irises are for the most part of the easiest culture; they grow in any good free garden soil, the smaller and more delicate species only needing the aid of turfy ingredients, either peaty or loamy, to keep it light and open in texture. The earliest to bloom are the dwarf forms of Iris pumila, which blossom during March, April and May; and during the latter month and the following one most of the larger growing species, such as I. germanica, florentina, pallida, variegata, amoena, flavescens, sambucina, neglecta, ruthenica, &c., produce their gorgeous flowers. Of many of the foregoing there are, besides the typical form, a considerable number of named garden varieties. Iris unguicularis (or stylosa) is a remarkable winter flowering species from Algeria, with sky-blue flowers blotched with yellow, produced at irregular intervals from November to March, the bleakest period of the year.

The beautiful Japanese Iris Kaempferi (or I. laevigata) is of comparatively modern introduction, and though of a distinct type is equally beautiful with the better-known species. The outer segments are rather spreading than deflexed, forming an almost circular flower, which becomes quite so in some of the very remarkable duplex varieties, in which six of these broad segments are produced instead of three. Of this too there are numberless varieties cultivated under names. They require a sandy peat soil on a cool moist subsoil.

What are known as Oncocyclus, or cushion irises, constitute a magnificent group of plants remarkable for their large, showy and beautifully marked flowers. Compared with other irises the “cushion” varieties are scantily furnished with narrow sickle-shaped leaves and the blossoms are usually borne singly on the stalks. The best-known kinds are atrofusca, Barnumae, Bismarckiana, Gatesi, Heylandiana, iberica, Lorteti, Haynei, lupina, Mariae, meda, paradoxa, sari, sofarana and susiana—the last-named being popularly called the “mourning” iris owing to the dark silvery appearance of its huge flowers. All these cushion irises are somewhat fastidious growers, and to be successful with them they must be planted rather shallow in very gritty well-drained soil. They should not be disturbed in the autumn, and after the leaves have withered the roots should be protected from heavy rains until growth starts again naturally.

A closely allied group to the cushion irises are those known as Regelia, of which Korolkowi, Leichtlini and vaga are the best known. Some magnificent hybrids have been raised between these two groups, and a hardier and more easily grown race of garden irises has been produced under the name of Regelio-Cyclus. They are best planted in September or October in warm sunny positions, the rhizomes being lifted the following July after the leaves have withered.