The Gum-Cistus is generally called, in the nurseries, Cistus ladaniferus; but it differs materially from the plant so named by Linnæus, as that has a ten-celled capsule, while the capsule of the common Gum-Cistus (which botanists call C. Cyperius) has only five cells. The leaves also differ, the under surface of those of the one kind being woolly, and of the other smooth; the one is also a native of Spain and Portugal, and the other, as the specific name imports, of Cyprus. Both species, and also C. Ledon, exude from their stems and leaves, a kind of gum or resin called Ladanum or Labdanum, which is used in medicine. It is from this gum having been formerly always mixed with opium when that drug was dissolved in spirits of wine, that the name of laudanum is given to the tincture of opium.
The two genera, Cistus and Helianthemum, differ chiefly in the capsule, which in the latter genus is triangular and one-celled, opening into three valves, each of which has a narrow dissepiment down its centre. To prevent any confusion arising from the use of these terms, I may here observe that when a capsule is divided into several cells, having no communication with each other, the membranes that separate them are called dissepiments; while the nerve-like part of it to which the seeds are attached is named the placenta. Sometimes the placenta is merely a nerve running down the side of the capsule, when the capsule is one-celled, without any dissepiment or division; and sometimes the dissepiment does not spread across the capsule so as to divide it into different cells, but only projects a little way from the side towards the centre, as in the one-celled capsule of the Poppy, (see p. [260],) and in that of the Helianthemum, when the seed-vessel opens naturally into different parts, as in the Gum Cistus, these parts are called valves, as are also the parts of pods, as shown in the curled-up valves of the silique, fig. 115, in p. 268.
To return to the Helianthemum, the species of this genus are generally used for rockwork, as they are all dwarf plants, though many of the genus Cistus are large shrubs four or five feet high. The English name of the Helian themum, Sun-rose, is very appropriate, as the flowers will only expand in sunshine, and will even decay in the bud without opening at all, when gloomy weather lasts for several days.
ORDER XX. VIOLACEÆ—THE VIOLET TRIBE.
The order Violaceæ, though not a large one, contains several genera, but the most interesting is the genus Viola, which includes among many other species the Sweet Violet (Viola odorata), and the Heartsease (V. tricolor). The flowers of both species have many claims to admiration, but they do not add the charm of regularity in construction to their other attractions, as, in fact, few flowers are less symmetrical. The flowers of both are nearly alike in their details; but to avoid confusion, I will describe them separately. The calyx of the Heartsease consists of five pointed distinct sepals, two of them rather smaller than the others. These sepals are not attached, as in most other plants, at their base; but so as to leave nearly a quarter of their length standing up, far beyond the place where they are fixed to the receptacle, so as to form a sort of border or cup round the stem, and between it and the flower. The sepals are green, but they are edged with a delicate whitish membrane at the margin, scarcely to be seen without a microscope. There are five petals which are also irregular in their construction, two of them being much larger than the others, and generally of a different colour; and one even of the other three being quite different in form to its companions. The two large petals at the back of the flower, which in the common Heartsease are generally dark purple, are laid over each other, and behind the two below them. These two side-petals, which form the centre of the flower, are both furred at the base; and the lower petal, which is placed between them, has its claw drawn out behind into a spur, which passes between two of the sepals; and which, when the flower is looked at from behind, appears to be part of the calyx. The furred part of the two side-petals forms a triangular, roof-like opening, peeping out of which, is seen a small pale-green ball-like substance, which a fanciful imagination might liken to a head looking through a dormer window; and this is all that is to be seen in place of the usual apparatus of stamens and pistils. As all seed-producing flowers must have stamens and pistils, and as it is well known that Heartseases and Violets do produce seed in abundance, it is clear that these important organs are not wanting; but where are they? It is easy to guess, after being so far initiated in the mysteries of botany, that the little globular body is a part of the pistil; but where are the stamens? It is necessary to pull the flower to pieces to discover them. Commencing this work of destruction, which I always feel remorse at perpetrating, for I love flowers too well not to feel pain at destroying them; commencing this work, I repeat, the petals and the sepals must be carefully removed from the stem; a task of some little difficulty, as both sepals and petals are firmly attached to the receptacle, and the lower petal must have its spur opened with a pin to avoid hurting the delicate organs it contains. When the outer coverings of calyx and corolla are thus both removed, the seed-producing organs will be discovered, and it will be found that they consist of five very curiously-formed stamens, with as singular a pistil, in their centre. The stamens have no apparent filaments, and the anthers, which seem to be inserted in the receptacle, look like seeds, each tipped with a bit of brown skin, and having what appears to be a white rib in front. This rib is the anther; and the broader part is the dilated filament, which is drawn out beyond it, on both sides, and above, so as to form the brown tip above the anther already mentioned. Two of the anthers have each, in addition to these peculiarities, a long tail, which the spur of the lower petal concealed, when the flower was in a perfect state. The pistil consists of a large ovary, full of ovules, with a narrow style, which is drawn out into the hollow globular termination which is seen through the triangular opening in the flower. The globe has an opening in front, under which is a kind of lip, which looks like a shutter let down to show the opening; and though, from its thick fleshy nature, it looks like a stigma, it is only the outer covering of that organ, for the stigma lies within the opening. In this manner the stigma and anthers are completely concealed; and thus it will be seen, that nothing can be more complex and intricate than the construction of the flowers of the Heartsease.
Who could suppose that all these elaborate details would be necessary to illustrate so simple a flower as that of the Violet? And yet the construction of the flowers of the Violet and those of the Heartsease are essentially the same. The sepals of the Violet are extended at the base, like those of the Heartsease, and the corolla consists of the same number of petals, which are equally irregular in their form, though not in their colour; the lower petal is drawn out, in the same manner, into a spur, which is much longer than that of the Heartsease, though the rest of the flower is smaller. The stamens are formed with the same regular irregularity, only the tails of the two irregular ones are larger and stronger, in the same proportion as the spur is larger which is intended to conceal them. The pistil is of the same shape, with the same curiously constructed and perforated style, which is bent in its narrow part and swelled out into a hollow globe at the tip; and in both species, the ovary is one-celled with three parietal placentas, that is, with three nerve-like projections from the sides of the capsule, having four rows of seeds attached to each. The capsule looks like a smooth shining berry, and it remains partially shrouded by the calyx, till the seeds are ripe; when it bursts open with an elastic spring, and divides into three valves, each of which has the placenta bearing the seeds in its centre.
In all these points the Heartsease and the Violet are alike; but they differ materially in the leaves, which in the Violet are broad and heart-shaped, without stipules; but in the Heartsease are small and ovate, with such very large and deeply-cut stipules, that they are by most persons mistaken for the leaves. I may here be asked what are stipules, and in what do they differ from leaves? In answer to the first question, I can only inform my readers that stipules are generally little leaf-like bodies, which seem to act as attendants upon leaves, as bracts seem to wait upon flowers; but in what they differ from leaves, except in size and shape, I have not been able to learn. Even Dr. Lindley in the last edition of his Introduction to Botany, says, “What stipules really are is not well made out.”
The Heartsease and the Violet differ also in their habit of growth. The Violet is a creeping plant with no stalks but those supporting the flowers, while the Heartsease stands erect, with a thick square stem, so strong, that, notwithstanding its succulent nature, it may be trained like a little tree.