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.
IRISH MOSS, or Carrageen (Irish carraigeen, “moss of the
rock”), a sea-weed (Chondrus crispus) which grows abundantly
along the rocky parts of the Atlantic coast of Europe and North
America. In its fresh condition the plant is soft and cartilaginous,
varying in colour from a greenish-yellow to a dark purple or
purplish-brown; but when washed and sun-dried for preservation
it has a yellowish translucent horn-like aspect and consistency.
The principal constituent of Irish moss is a mucilaginous
body, of which it contains about 55%; and with that it has
nearly 10% of albuminoids and about 15% of mineral matter
rich in iodine and sulphur. When softened in water it has a
sea-like odour, and from the abundance of its mucilage it will
form a jelly on boiling with from 20 to 30 times its weight of
water. The jelly of Irish moss is used as an occasional article
of food. It may also be used as a thickener in calico-printing
and for fining beer. Irish moss is frequently mixed with Gigartina
mammillosa, G. acicularis and other sea-weeds with which it is
associated in growth.
IRKUTSK, a government of Asiatic Russia, in East Siberia,
bounded on the W. by the government of Yeniseisk, on the N. by Yakutsk, on the E. by Lake Baikal and Transbaikalia
and on the S. and S.W. by Mongolia; area, 287,061 sq. m.
The most populous region is a belt of plains 1200 to 2000 ft. in
altitude, which stretch north-west to south-east, having the
Sayan mountains on the south and the Baikal mountains on the
north, and narrowing as it approaches the town of Irkutsk. The
high road, now the Trans-Siberian railway, follows this belt.
The south-western part of the government is occupied by
mountains of the Sayan system, whose exact orography is as
yet not well known. From the high plateau of Mongolia, fringed
by the Sayan mountains, of which the culminating point is the
snow-clad Munko-sardyk (11,150 ft.), a number of ranges,
7500 to 8500 ft. high, strike off in a north-east direction. Going
from south to north they are distinguished as the Tunka Alps,
the Kitoi Alps (both snow-clad nearly all the year round), the
Ida mountains and the Kuitun mountains. These are, however,
by no means regular chains, but on the contrary are a complex
result of upheavals which took place at different geological
epochs, and of denudation on a colossal scale. A beautiful,
fertile valley, drained by the river Irkut, stretches between the
Tunka Alps and the Sayan, and another somewhat higher plain,
but not so wide, stretches along the river Kitoi. A succession
of high plains, 2000 to 2500 ft. in altitude, formed of horizontal
beds of Devonian (or Upper Silurian) sandstone and limestone,
extends to the north of the railway along the Angara, or Verkhnyaya
(i.e. upper) Tunguzka, and the upper Lena, as far as
Kirensk. The Bratskaya Steppe, west of the Angara, is a
prairie peopled by Buriats. A mountain region, usually described
as the Baikal range, but consisting in reality of several
ranges running north-eastwards, across Lake Baikal, and
scooped out to form the depression occupied by the lake, is
fringed on its north-western slope by horizontal beds of sandstone
and limestone. Farther north-east the space between the Lena
and the Vitim is occupied by another mountain region belonging
to the Olekma and Vitim system, composed of several parallel
mountain chains running north-eastwards (across the lower
Vitim), and auriferous in the drainage area of the Mama (N.E.
of Lake Baikal). Lake Baikal separates Irkutsk from Transbaikalia.
The principal rivers of the government are the Angara,
which flows from this lake northwards, with numerous sharp
windings, and receives from the left several large tributaries.
