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ORCHIDS

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Originally appearing in Volume V20, Page 172 of the 1911 Encyclopedia Britannica.
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ORCHIDS . The word Orchis is used in a See also:

special sense to denote a particular genus of the Orchid See also:family (Orchidaceae) ; very frequently, also, it is employed in a more See also:general way to indicate any member of that large and very interesting See also:group. It will be convenient here to use the word Orchis as applying to that particular genus which gives its name to the See also:order or family, and to employ the See also:term " orchid " in the less precise sense. The See also:flowers of all orchids, though extremely diverse within certain limits, and although superficially very different from those of other monocotyledons, are all formed upon one See also:common See also:plan, which is only a modification of that observable in such flowers as those of the See also:narcissus or See also:snowdrop (Galanthus). The conformation of those flowers consists essentially in the presence of a six-parted perianth, the three See also:outer segments of which correspond to a calyx, the three inner ones to a corolla. These segments See also:spring apparently from the See also:top of the ovary—the real explanation, however, being that the end of the See also:flower-stalk or "thalamus," as it grows, becomes dilated into a sort of See also:cup or See also:tube enclosing and indeed closely adhering to the ovary, so that the latter See also:organ appears to be beneath the perianth instead of above it as in a See also:lily, an See also:appearance which has given origin to the term " inferior ovary." Within the perianth, and springingfrom its sides, or apparently from the top of the ovary, are six stamens whose anthers contain pulverulent See also:pollen-grains. These stamens encircle a See also:style which is the upward continuation of the ovary, and which shows at its See also:free end traces of the three originally See also:separate but now blended carpels of which the ovary consists. An orchid flower has an inferior ovary like that just described, but with the ovules on the walls of the cavity ( not in its See also:axis or centre), a six-parted perianth, a stamen or stamens and stigmas. The See also:main distinguishing features consist in the fact that one of the inner pieces of the perianth becomes in course of its growth much larger than the See also:rest, and usually different in See also:colour, texture and See also:form. So different is it that it receives a distinct name, that of the " See also:lip " or " labellum." In See also:place of the six stamens we commonly find but one (two in Cypripedium), and that one is raised together with the stigmatic surfaces on an See also:elongation of the floral axis known as the "See also:column." Moreover, the pollen, instead of consisting of separate cells or grains, consists of cells aggregated into "pollen-masses," the number varying in different genera, but very generally two, four, or eight, and in many of the genera provided at the See also:base with a strap-shaped stalk or "caudicle" ending in a flattish gland or "viscid disk" like a boy's sucker. In Cypripedium all three stigmas are functional, but in the See also:great See also:majority of orchids only the lateral pair form receptive surfaces (st, fig. 3), the third being sterile and forming the rostellum which plays an important See also:part in the See also:process of See also:pollination, often forming a See also:peculiar pouch-like process (fig.

4, r) in which the viscid disk of the pollen-masses is concealed till released in the manner presently to be mentioned. It would appear, then, that the orchid flower differs from the more general monocotyledonous type in the irregularity of the perianth, in the suppression of five out of six stamens, and in the See also:

union of the one stamen and the stigmas. In addition to these modifications, which are common to nearly all orchids, there are others generally but not so universally met with; among them is the displacement of the flower arising from the twisting of the inferior ovary, in consequence of which the flower is so completely turned See also:round that the " lip," which originates in that part of the flower, conventionally called the posterior or See also:superior part, or that A A. Floral See also:diagram of typical orchid flower; 1, labellum; a, anther; s, rudiments of barren stamens (staminodes). B. Diagram of the symmetrical trimerous flower of See also:Fritillary (Fritillaria). p1- $ of Orchis. s, sl, sl, The three divisions of the outer perianth. pl, p1, The two lateral divisions of the inner perianth. The superior See also:division or the labellum, which may become inferior by the twisting of the ovary. e, The fertile stamen, with its two pollen-masses in the anther-lobes. c, The one-celled ovary cut transversely, having three parietal placentas.

PS, s, s, s, The three outer divisions of the perianth. p, p,1, The three inner, 1 being the labellum, here inferior by the twisting of the ovary. e, See also:

Spur of the labellum. o, The See also:twisted ovary. st, The stigma. a, The anther, containing pollen-masses. Sepals. Petals. Anther. Two See also:united stigmas. Rostellum (barren stigma). s, p, a, st, r, nearest to the supporting See also:stem, becomes in course of growth turned to the anterior or See also:lower part of the flower nearest to the bract, from whose axil it arises. Other common modifications arise from the union of certain parts of the perianth to each other, and from the varied and often very remarkable outgrowths from the lip.

These modifications are associated with the structure and habits of See also:

insects and their visits to the flowers. See also:Cross fertilization, or the impregnation of any given flower by pollen from another flower of the same See also:species on the same or on another plant, has been proved to be of great —g See also:advantage to the plant by securing a more In the common orchids of See also:British meadows, Orchis Morro, mascula (See also:Shakespeare's See also:long purples), &c., the general structure of the flower is as we have described it (See also:figs. 2, 3). In addition there is in this particular genus, as indeed in many others, a long tubular spur or See also:horn projecting downwards from the back of the lip, whose See also:office it is to secrete and See also:store a honeyed juice; the forepart of the lip forms an See also:expanded See also:plate, usually larger and more brightly coloured than the other parts of the flower, and with hairs or ridges and spots of various kinds according to the species. The remaining parts of the perianth are very much smaller, and commonly are so arranged as to form a See also:hood over-arching the " column. " This column stands up from the base of the flower, almost at right angles to the lip, and it bears at the top an anther, in the two hollow lobes of which are concealed the two pollen-masses, each with its caudicle terminating below in a roundish gland, concealed at first in the pouch-like rostellum at the front of the column. Below the anther the See also:surface of the column in front is hollowed out into a greenish depression covered with viscid fluid—this is the two united stigmas. The other parts of the flower need not detain us. Such being in general terms the mechanism of the flower of a common orchis, let us now see how it acts. A See also:bee, we will assume, attracted by the colour and perfume of the flower, alights on that part of it which is the first to attract its See also:attention—the lip. There, guided by the hairs or ridges before-mentioned, it is led to the orifice of the spur with its store of honeyed juice. The position of this orifice, as we have seen, is at the base of the lip and of the column, so that the See also:insect, if of sufficient See also:size, while bending its See also:head to insert the See also:proboscis into the spur, almost of See also:necessity displaces the pollen-masses.

Liberated from the anthers, these adhere to the head or back of the insect by means of the sticky gland at the bottom of the caudicle (fig. 4). Having attained its See also:

object the insect withdraws, taking the pollen-masses, and visits another flower. And now occurs another See also:device or See also:adaptation noless marvellous than those of which mention has been made. The two anther-cases in an orchis are erect and nearly parallel the one to the other; the pollen-masses within them are of course in like See also:case, as may be thus represented II, but immediately the pollen-masses are removed movements take place at the base of the caudicle so as to effect the bending of this stalk and the placing the pollen-See also:mass in a more or less See also:horizontal. position, thus -, or, as in the case of 0. pyramidalis, the two pollen-masses originally placed parallel I I diverge from the base like the See also:letter V. The movements of the pollen-masses may readily be seen with the naked See also:eye by thrusting the point of a See also:needle into the base of the anther, when the disks adhere to the needle as they would do to the antenna of an insect, and may be withdrawn. Sometimes the lip is See also:mobile and even sensitive to impressions, as are also certain processes of the column. In such cases the contact of an insect or other See also:body with those processes is sufficient to liberate the pollen often with elastic force, even when the anther itself is not touched. In other orchids movements take place in different ways and in other directions. The object of these movements will be appreciated when it is re-membered that, if the pollen-masses retained the See also:original direction they had in the anther in which they were formed, they would, when transported by the insect to another flower, merely come in contact with the anther of that flower, where of course they would be of no use; but, owing to the divergences and flexions above alluded to, the pollen-masses come to be so placed that, when transplanted to another flower of the same species, they come in contact with the stigma and so effect the fertilization of that flower. These illustrations are comparatively See also:simple; it would have been easy to select others of a more complicated nature, but all evidently connected with the visits of insects and the cross fertilization of the flower. In some cases, as in Catasetum, male flowers are produced so different from the See also:female that before the different flowers had been found on the same See also:pike, and before the facts of the case were fully known, they were taken to be representatives of distinct genera.

The See also:

fruit is a See also:capsule splitting generally by three See also:longitudinal slits forming valves which remain united above and below. The seeds are See also:minute and innumerable; they contain a small rudimentary embryo surrounded by a thin loose membraneous coat, and are scattered by means of hygroscopic hairs on the inside of the valves which by their movements jerk out the seeds. The floral structure is so curious that perhaps less attention has been paid to the vegetative See also:organs than the peculiarities of their organisation demand. We can only allude to some of these points. The orchids of British See also:fields are all of terrestrial See also:habit, and their roots are mostly tuberous (fig. 6), the tubers being partly See also:radical partly budlike in their See also:character. There is often a marked alter-nation in the See also:production of vegetative and flowering shoots respectively; and, some-times, from various circumstances, the flowering shoots are not produced for several years in See also:succession. This fact will See also:account for the profusion with which some orchids, like the common bee orchis for instance, are found in some seasons and their scarcity in others. Tropical orchids are mostly epiphytal—that is, they grow upon trees without deriving nourishment from them. They are frequently provided with " pseudo-bulbs, " large solid swellings of the stem, in the tissues of which See also:water and nutritive materials are stored. They derive this moisture from the See also:air by means of aerial roots, See also:developed from the stem and bearing an outer spongy structure, or velamen, consisting of empty cells kept open by See also:spiral thickenings in the See also:wall; this sponge-like See also:tissue absorbs See also:dew and See also:rain and condenses the moisture of the air and passes it on to the See also:internal tissues. 172 The number of species of orchids is greater than that of any other monocotyledonous order—not even excepting See also:grasses—amounting to 6000, contained in 400 genera.

This large number is partly accounted for by the diligent See also:

search in all countries that has been made for these See also:plants for purposes of cultivation—they being held at See also:present in the greatest esteem by plant-lovers, and prices being paid for new or rare varieties which recall the days of the tulipomania. The economic uses of orchids are not remarkable. When we have mentioned See also:vanilla (q.v.), which consists of the fleshy pods . of an orchid, we have mentioned about the only economic product that now comes into See also:market. See also:Salep (q.v.), still used in the See also:Levant, consists of the dried tubers of a terrestrial orchid, and contains a relatively large amount of nutritious See also:matter. The cultivation of orchids is treated under See also:HORTICULTURE. The order is divided into two main See also:groups based on the number of the stamens and stigmas. The first Diandreae, has two or rarely three fertile stamens and three functional stigmas. It contains two small genera of tropical See also:Asia and See also:Africa with almost See also:regular flowers, and the large genus Cypripedium containing about 8o species in the See also:north-temperate See also:zone and tropical Asia and See also:America. In Cypripedium two stamens are present, one on each See also:side of the column instead of one only at the top, as in the group Monandreae, to which belong the remaining genera in which also only two stigmas are fertile. What may be considered the normal number of stamens is, as has been said, six, arranged in two rows. In most orchids the only stamen developed to maturity is the posterior one of the three opposite to the lip (anterior before the twisting of the ovary), the other two, as well as all three inner ones, being entirely absent, or present only in the form of rudiments. In Cypripedium two of the outer stamens are wanting; the third—the one, that is, which corresponds to the single fertile stamen in the Monandreae—forms a large sterile structure or staminode; the two lateral ones of the inner See also:series are present, the third being undeveloped.

This arrangement may be understood by reference to the following diagram, representing the relative position of the stamens in orchids generally and in Cypripedium. The letter L indicates the position of the labellum; the large figures indicate the developed stamens; the See also:

italic figures show the position of the suppressed stamens. 4 6S 465 2 L 3 2 L 3 Arrangement of stamens Arrangement of stamens in Orchis. in Cypripedium. The Monandreae have been subdivided into twenty-eight tribes, the characters of which are based on the structure of the anther and pollinia, the nature of the inflorescence, whether terminal or lateral, the vernation of the See also:leaf and the presence or See also:absence of a See also:joint between blade and sheath, and the nature of the stem. The most important are the following: Ophrydineae, with about 45 genera, of terrestrial orchids, mainly north temperate, including the British genera Orchis, Aceras, Ophrys, Herminium, Gymnadenia and Habenaria. Also some genera mainly represented in See also:South and tropical Africa, such as Satyrium, Disa andtemperate Asia and South Africa; Eulophia and Lissochilus are important See also:African genera. Cataselinae, with three tropical See also:American genera, two of which, Cataselunc and Cycnoches, have di- or tri-morphic flowers. They are cultivated for their See also:strange-looking flowers. Dendrobiinae, with six genera in the warmer. parts of the Old See also:World; the See also:chief is Dendrobium, with 300 species, often with showy flowers. Cymbidiinae, with 8 genera in the tropics of the Old World. The leaves are generally long and narrow. Cymbidium is well known in cultivation.

Oncidiinae, with 44 genera in the warmer parts of America. Odontoglossum and Oncidium include some of the best-known cultivated orchids. Sarcanthinae, with 42 genera in the tropics. Vanda (Asia) and Angraecum (Africa and See also:

Madagascar) are known in cultivation. The flower of Angraecum sesquipedale has a spur 18 in. in length. The order is well represented in See also:Britain by i8 genera, which include several species of Orchis:—Gymnadenia (fragrant orchis), Habenaria (butterfly and See also:frog orchis), Aceras (See also:man orchis), Herminium (See also:musk orchis), Ophrys (bee, spider and See also:fly orchis), Epipactis (Helleborine), Cephalanthera, Neottia (See also:bird's-See also:nest orchis), one of the few saprophytic genera, which have no See also:green leaves, but derive their nourishment from decaying organic matter in the See also:soil, Listera (Tway blade), Spiranthes (See also:lady's tresses), Malaxis (See also:bog-orchis), Liparis (fen-orchis), Corallorhiza (See also:coral See also:root), also a saprophyte, and Cypripedium (lady's slipper), represented by a single species now very rare in See also:limestone districts in the north of See also:England.

End of Article: ORCHIDS

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