ORDER PASSIFLOREE, OR PASSION-FLOWER TRIBE. 419

representation of the crucifixion and sufferings of our Saviour. In its anthers, they saw his five wounds; in the three styles, the

nails by which he was fixed to the cross; in the column which rises from the bottom of the flower, the pillar to which he was bound; and a number of little fleshy threads which spread from its cup, they compared to the crown of thorns. It seems difficult to imagine how such a notion could have been suggested to them; since the general aspect of the flower does not appear such as to be likely to excite it. Various species of Passion Flower,are now naturalized in this country; and are beautiful ornaments to the fronts of houses, garden walls, or trellis work, over which they may be trained. They sometimes climb to the tops of high trees, and hang down in elegant festoons from their branches. On examining the flower, we find that the calyx has five sepals, which are usually green on the outside, but are yellow, red, blue, or purple in their interior. The petals are equal in number to the sepals, and are of the same colour with their inside; sometimes, however, they are absent. Next within these, we do not at once come, as we might expect, to the stamens; but we meet with several rings of beautiful fleshy threads, which spread from the calyx like rays, and are splendidly variegated with crimson or blue and white. These diminish in size towards the centre of the flower; and at last lose themselves as it were, in some little rings that surround the base of the column which now presents itself in the centre. These threads are to be regarded

420

PASSION-FLOWER TRIBE.

either as stamens or petals in an undeveloped state; it is of no consequence which we denominate them. In the centre of the

flower, from the

Fig. 92. A, section of Passion-flower. B, central column, showing the 3 styles at the top; the five anthers a, a; the tube, b, b, formed by the cohesion of the filaments; c, the innermost ring of the undeveloped petals; d. the origin of the petals; e, the origin of the calyx.

in colour the

surrounding bodies, consists

of an exterior sheath, formed

by the adhesion

of the filaments to each other, and of an interior solid stalk, on the top of which the ovary is mounted. The ovary when cut across, is found to consist of but one cavity; the ovules, however, are attached to three parietal placenta (as in the Violet,) showing that the seedvessel is composed of three carpels; and the summit of the ovarium bears three short styles, wich terminate in thick swollen stigmas. The fruit is a fleshy egg-shaped body, containing a number of pulpy seeds; but it varies extremely in size and colour in the different species. In all instances, however, it is destitute of any injurious principle, and may be eaten with safety. In the common Passion-flower, it is about as large as a hen's egg, and orange yellow on its exterior; in some tropical species, called Grena dillas, it is much larger, attaining the size of a man's head, and is greener in its colour. These are cultivated on account of the slightly acid pulp they contain, which renders them refreshing; and the rind, which is also a little acid, is cut into slices and made into tarts which have somewhat the flavour of those of apples. The substance which surrounds the seeds is not mere pulp, but is

ORDER CRASSULACEE, OR HOUSE-LEEK TRIBE.

421

a sort of fleshy coat, termed the arillus, which gradually rises from the bottom of the ovule, and at last envelopes it completely. It will hereafter be seen that the spice known as mace is the arillus of the nutmeg. A species of Passion-flower inhabiting the Isle of France is remarkable for the narcotic properties of its root; but it is not unlikely that these are shared in some degree by others.

609. Passing over several small orders, we come to that of CRASSULACEE, the House-leek tribe, which is chiefly interesting as containing several British species of succulent plants, which flourish under circumstances that would be fatal to almost all others. They are found in the driest situations, where not a blade of grass nor a particle of moss can grow, on naked rocks, old walls, sandy hot plains, alternately exposed to the heaviest dews of night, and to the fiercest rays of the noon-day sun. Soil is to them something to keep them stationary, rather than a source of nutriment. In this respect they resemble the Cacti and other plants of tropical climates, which they represent in more temperate regions. About half of the species known to Botanists are natives of the Cape of Good Hope; and nearly half the remainder are European plants. Although they resemble the Cacti, and some other orders, in the succulent nature of their stems and leaves, there is no other very close correspondence between them. The number of parts in the flower is subject to great variation. The calyx may consist of from three to twenty sepals, which are united at the base. The petals are equal in number to the sepals, and are inserted into the calyx; they are sometimes distinct, and sometimes cohere into a monopetalous corolla. The stamens are either equal in number to the petals, alternating with them; or are twice as many, in which case those alternating with them are longer and come to maturity earlier than the others. The carpels are equal in number to the petals, and are opposite to them; they are arranged in a circle, and are more or less adherent in different species, each having its own style and stigma. Every one contains several ovules, which are arranged in two series along its internal edge, where the dehiscence or opening usually takes place at the time of maturity. The Sedums or Stonecrops, of which many

422

HOUSE-LEEK TRIBE; ORDER CACTEE.

species exist in Britain, belong to the Linnæan class and order DECANDRIA Pentagynia, having five parts in the calyx, corolla, and ovarium, with double the number of stamens; whilst the Sempervivum, or House leek, is found under DODECANDRIA Dodecagynia, having twelve stamens and twelve styles. The common British species of the latter is remarkable for almost always bearing ovules on its anthers, instead of pollen. These plants are not only very tenacious of life when naturally exposed to the elements, but resist efforts made to destroy their vitality, when it is desired to preserve them. The collector finds it very difficult, therefore, to prepare them for his Herbarium; for they will push long shoots whilst under great pressure, and after being submitted to a high temperature. It is from the deficiency of stomata, and the thickness of the cuticle, that it is so difficult to dry them; and it is obviously by these properties, that they are enabled to resist the rays of the sun. 610. The order CACTEE, or Prickly Pear tribe, is by nature

of Cactus.

exclusively confined to the New World; but several species have now been naturalized elsewhere. They do not, even on that continent, extend far from the tropics they frequent hot, dry, exposed situations, like those to which the Crassulaceae are adapted. Most of the species of this order are remarkable for the absence of leaves, of which no other traces are found than tufts of prickles arising at regular intervals from the stem,-these being the veins of the leaves between which the parenchyma

Fig. 93. Stem, branch, and flower is not developed (§ 236). The stems and branches are very fleshy and succulent, and usually have flat expanded surfaces, which in some degree perform the functions of leaves. In

CACTUS, OR PRICKLY-PEAR TRIBE.

423 the various species of Cactus, however, we find the form of the stem differing greatly. Thus in one kind, known as the Melon Cactus from its form, the stem is so much stunted as well as expanded, that it quite resembles the fruit alluded to. In other species, however, the stems are round and greatly prolonged, resembling ropes; whilst in others, again, they are equally long, but are angular. All are adapted to the same circumstances of growth; but the Melon-Cactus, from its greater bulk, in proportion to the surface it presents, can exist in the most exposed situations. It usually happens in tropical climates, that during a certain portion of the year, a large quantity of rain falls, the atmosphere is loaded with dampness for many weeks, and the soil is completely saturated with water. During this time, the Cactuses live very fast, and distend all the cavities of their tissue with fluid. The resistance afforded by their thick cuticle, and by the deficiency of stomata, to the evaporation of this, enables them to retain a store of it (as the Camel holds water in the stomach) until they can acquire a fresh supply. At other times, they may be said to live very slowly; the functions of exhalation, digestion, &c., are performed very inactively; and the fluid which they have absorbed during the rainy season is adequate for their support, during all those months when they cannot live upon the soil or the atmosphere. This property sometimes renders the Cactus tribe of great utility On Mount Etna, for example, and its volcanic fields, it is the Indian Fig which the Sicilians employ, to render such desolate regions susceptible of cultivation. This plant readily strikes into the fissures of the lava, and soon, by extending the ramifications of its roots into every crevice of the stone, and bursting the largest blocks asunder by their gradual increase, makes it capable of being worked. The juiciness of the stems causes them to be sought in the West Indies, during dry seasons, by the cattle, which, tearing off the thorny integument that covers them, feed upon the moist pulp within.

to man.

611. The flowers of this tribe are commonly very chowy; and the number of handsome species, which have been of late introduced into our hothouses, gives them an air of splendour unknown