Almost invariably insect aid is required to transport the pollen from flower to flower: hence the importance of the contrivances indicated above (to which Mr. Darwin some years ago directed attention), to insure the proper fulfilment of the important function assigned to unconscious agents.

Compare with Spotted Orchis the flowers of Pyramidal Orchis (O. pyramidalis) and Bee Orchis (Ophrys apifera). In Pyramidal Orchis, the two pollinia of each anther are united to a single saddle-shaped disk, so that they can only be removed together. In the Bee Orchis, the caudicles are so weak, that when the anther-cells open, the pollen-masses topple over in front and dangle opposite to the viscid stigma, the glands remaining in the rostellum. A puff of wind forces the suspended pollen-masses against the stigma, so that in this species self-fertilization appears usually to obtain.

Remarkable modifications of these processes occur in exotic species. An Orchis should not be passed by in flower without experimenting upon its pollinia until the mode of its fertilization be understood.

The form of the labellum varies very much in different species, assuming sometimes grotesque shapes. The flowers of many tropical species are very beautiful and often singularly fantastic, so that they are favourites in hot-house cultivation, and are often sold at a very high price.

Many of the tropical species are called "air-plants," from their being epiphytal-that is, growing upon the trunks of trees without becoming organically united to them as parasites. They cling to the bark by long greenish or white aerial roots, and absorb moisture partly from the air and partly from what trickles down the tree, charged with decaying organic and with inorganic matter. The lower internodes of the stem of these epiphytal Orchids often become swollen, forming what are called pseudo-bulbs.

One extremely rare British species, the Lady's Slipper (Cypripedium Calceolus), represents a Sub-type of the Order, differing from the Type in having 2 lateral anthers developed instead of the single posterior one, which is abortive in this genus.

FIG. 176.-Column of Lady's Slipper.

An American genus, Vanilla, affords a fragrant fruit, imported as Vanilla, and used in flavouring confectionery. 69. Natural Order-Irideæ. The Iris Family. DISTRIBUTION.-Occurring in both hemispheres; most numerous in the temperate zones, and more especially at the Cape.-British genera 4, species 6.

Herbs. Perianth-leaves 6. Stamens 3. Ovary inferior.
Type-Yellow Flag (Iris pseudacorus).

A perennial herb with a thick shortly-creeping rhizome, distichous sword-shaped leaves, and showy yellow hermaphrodite flowers.

OBSERVE the equitant bases of the leaves, which are folded up the mid-rib and vertically flattened throughout, having the two sides of their upper surface coherent in the upper part of the leaf, so that each exposed surface

of the leaf answers really to one half of the lower surface. Observe, also, the stamens concealed under arching, petal-like stigmas; the stigmatic surface is confined to a transverse line on the under surface of the latter.

Several handsome garden species belong to this Order, as the Blue Flag (I. germanica), and White Flag (I. florentina), two of the species the rhizome of which is dried as Orris Root; also the genera Gladiolus and Crocus. From a purple-flowered species of Crocus (C. sativus), Saffron, formerly in great esteem as a drug, is obtained. It consists of the stigmas pressed into cakes and dried. This Crocus used to be cultivated at Saffron Walden, in Essex, which place was chartered with arms, bearing three Saffron Crocuses, by Edward VI. An acre produced from 8 lbs. to 20 lbs. of Saffron. It is given to sick canaries, but its reputation has long been lost, and it is now chiefly used to colour other medicines. It is stated that a single grain of Saffron will impart distinct coloration to ten gallons of water.

70. Natural Order- Amaryllideæ. Family.

The Amaryllis

DISTRIBUTION.-Widely scattered through tropical and temperate countries of both hemispheres, numerous in the Mediterranean region and at the Cape of Good Hope.-British genera 3, species 4.

Herbs. Perianth-segments 6. Stamens 6. Ovary inferior. Type-Daffodil (Narcissus pseudo-narcissus).

A bulbous herb, with radical linear leaves, a membranous spathaceous bract, and showy solitary regular flower, borne upon an erect glabrous scape.

OBSERVE the corona referred to at page 43. It is very much shorter in other species, as in the white-flowered Poet's Narcissus (N. poeticus) and Jonquil (N. Jonquilla). It is wanting in Snowdrop (Galanthus).

t

FIG. 177.-Vertical section of flower of Daffodil.

Amaryllidaceæ much resemble Lilies, differing principally in their inferior ovary.

The bulbs of several species yield a poisonous juice, and the flowers of Daffodil are said to be very poisonous. One of the most important exotic species is the socalled American Aloe (Agave americana), which has become thoroughly naturalized in countries bordering upon the Mediterranean. From the Agave the Mexicans prepare an intoxicating beverage in common use, called pulque."

71. Natural Order-Dioscoreaceæ. The Yam Family. DISTRIBUTION.-A small Order, chiefly confined to tropical and sub-tropical countries.-One British genus, species I.

Type-Black Bryony (Tamus communis).

A climbing herb, with alternate shining cordate leaves, small racemose unisexual flowers, and scarlet berries. (The only British species.)

N.B. This species, although commonly called Black Bryony, has nothing to do with the genus Bryonia, belonging to the Dicotyledonous Order Cucurbitacea (page 156). Black Bryony differs from most of the species of this Order in having a berried (baccate) instead of a capsular fruit.

A few species, belonging to the exotic genus Dioscorea, produce large tubers, which, under the name of Yams, form an important article of food in tropical countries. The rhizome of a Cape species (Testudinaria elephantipes), attaining an immense size, sometimes more than 3 ft. in thickness and height, is covered with a corky bark, and seems to endure for a very long period, throwing up annual stems, resembling those of the Black Bryony. From the appearance of the rhizome, it is called "Elephant's foot" at the Cape of Good Hope, where it was formerly eaten by the aborigines as Hottentot Bread."

66

72. Natural Order-Cyperaceae. The Sedge Family.

DISTRIBUTION.-A large Order, widely dispersed from the arctic zone to the equator, in both hemispheres. A large proportion of the species affect moist situations.— British genera 9, species 74-80.