The stamens are inserted upon the top of the tube of the corolla, and if you look at the base of their filaments you would be inclined to pronounce it a foliaceous expansion, or, rather, a metamorphic doubling of the corolla. Suppose the stamens to be the result of the transformation of the petals, the filament would be the "claw," and the anther the "limb" of a foliole. At least, theory would tell you so. But observation will show that these are not petals changing into stamens, but, on the contrary, stamens changing into petals; as is seen in the sterile (or "double") flowers of many of our ornamental plants, and even of some of our fruit trees. How, then, shall we conciliate theory with observation? Look, and you shall find.
Observe the anthers which surmount the filaments. There is something peculiarly characteristic in them. As they open and spread abroad the pollen, they visibly coil themselves up in the form of a spiral. (Fig. 58.) Owing to this twisting, they are found more or less inclined upon their filaments, and are gifted with a considerable mobility. Thoroughly to understand the relation between the continuous anther and the filament, we must examine the stamens before their expansion, while they are still folded up within the floral bud, their matrix. The anthers are then quite straight, and, with a magnifying-glass, you can easily see how they are inserted, by the lower part of their back, upon the top of the filament, whose (so-called) connective prolongation separates the two lobes of the pollen receptacle. The anthers are then introrse (introrsum, inwardly)—that is to say, their face being inclined inwards, they look towards the centre of the flower, occupied by the style, a filiform prolongation of the ovary; the apex of the style (stigma) is thick, globulose, and of a glandular structure. The fruit, resulting from the metamorphosis of the ovary, is an elongated fusiform capsule, composed of two lobes, each containing a very large number of extremely small seeds.
Fig. 58.—Anthers of the Centaury.
The characters we have just enumerated apply, or the majority of them, to the interesting family of the Gentianaceæ—a natural group of plants, nearly all remarkable for their bitter, febrifugal, and anti-scrofulous properties. The flowering cymes of the common centaury are very frequently employed as a substitute for the medicinal gentian, so well known as a valuable tonic.
The medicinal gentian is the Gentiana lutea,—a plant growing about three feet high,—which thrives abundantly on the Pyrenees, and the Alps of Switzerland and Austria, at an elevation of 3000 to 5000 feet. It is not, however, so common now as formerly on the Alpine heights, owing probably to its great consumption, but it is spreading into many districts of Central Europe.
Frequent enough in the vicinity of Paris is the Chlora perforata, a gentian remarkable for its glaucous leaves and yellow terminal flowers.
The Gentiana kurroo of the Himalayas, and the British species, Gentiana campestris and Gentiana amarella, possess the tonic properties of the family. The Cheritta of the pharmacopœia is the herb and root of Agathotes chirayta (Ophelia chirata), a herbaceous plant which flourishes in the Himalayas.
We must not omit a reference to a Lilliputian gentian, the filiform gentian of Linnæus, and the Exacum filiforme or Cicendia filiformis of other botanical authorities.