111.] WINGED SEEDS FREQUENT ON TREES.

69

is called, or leaf of the flower-stalk, serves the same purpose.

In a great many other plants the same result is obtained by flattened and expanded edges. A beautiful example is afforded by the genus Thysanocarpus, a North American crucifer; T. laciniatus has a distinctly winged pod; in T. curvipes the wings are considerably larger; lastly, in T. elegans and T. radians the pods are still further developed in the same direction, T. radians having the wing very broad, while in T. elegans it has become thinner and thinner in places, until at length it shows a series of perforations. Among our common wild plants we find winged fruits in the Dock (Rumex) and in the common Parsnip (Pastinaca). But though in these cases the object to be obtained—namely, the dispersion of the seed-is effected in a similar manner, there are differences which might not at first be suspected. Thus in some cases, as, for instance, the Pine, it is the seed itself which is winged; in Thlaspi arvense it is the pod; in Entada, a leguminous plant, the pod breaks up into segments, each of which is winged; in Nissolia the extremity of the pod is expanded into a flattened wing; lastly, in the Lime, as already mentioned, the fruits drop off in a bunch, and the leaf at the base of the common flower-stalk, or "bract," as it is called, forms the wing.

In Gouania retinaria of Rodriguez the same object is effected in another manner; the cellular tissue of the fruit crumbles and breaks away, leaving only the vascular tissue, which thus forms a net inclosing the seed.

20

70

FEATHERED SEEDS. WILLOW. [CHAP.

Another mode, which is frequently adopted, is the development of long hairs. Sometimes, as in Clematis, Anemone, and Dryas, these hairs take the form of a long feathery awn. In others the hairs form a tuft or crown, which botanists term a pappus. Of this the Dandelion and John Go-to-bed-at-noon, so called from its habit of shutting its flowers about mid-day, are well-known examples. Tufts of hairs, which are themselves sometimes feathered, are developed in a great many Composites, though some, as, for instance, the Daisy and Lapsana, are without them; in some very interesting species, of which the common Thrincia hirta of our lawns and meadows is one, there are two kinds of fruits, as shown in Fig. 48, b, one with a pappus and one without. The former are adapted to seek "fresh woods and pastures new," while the latter stay near the parent plant and perpetuate the race at home.

A more or less similar pappus is found among various English plants-in the Epilobium (Fig. 48, a), Thrincia (Fig. 48, b), Tamarix (Fig. 48, c), Willow (Fig. 48, d), Cotton Grass (Fig. 48, e), and Bulrush (Fig. 48, f); while in exotic species there are many other cases-as, for instance, the beautiful Oleander. As in the wings, so also in that of the pappus, it is by no means always the same part of the plant which develops into the crown of hairs. Thus in the Valerians and Composites it is the calyx; in the Bulrush the perianth; in Epilobium the crown of the seed, in the Cotton Grass it is supposed to represent the perianth; while in some, as, for instance, in the Cotton plant, the whole outer surface of the seed is

III.] WILLOW HERB. THRINCIA. BULRUSH. 71

clothed with long hairs.

Sometimes, on the contrary,

the hairs are very much reduced in number, as, for instance, in some species of Eschynanthus, where

FIG 48.

a, willow herb (Epilobium); b, two forms of seed of Thrincia hirta; c, Tamarix ; d, willow (Salix); e, cotton grass (Eriophorum); f, bulrush (Typha).

there are only three, one on one side and two on the other. In this case, moreover, the hairs are very

72

SEEDS WAFTED BY WATER. [CH. III.

flexible, and wrap round the wool of any animal with which they may come in contact, so that they form a double means of dispersion.

In other cases seeds are wafted by water. Of this the Cocoa-nut is one of the most striking examples. The seeds retain their vitality for a considerable time, and the loose texture of the husk protects them and makes them float. Every one knows that the Cocoanut is one of the first plants to make its appearance on coral islands, and it is, I believe, the only palm which is common to both hemispheres.

The seeds of the common Duckweeds (Lemna) sink to the bottom of the water in autumn, and remain there throughout the winter; but in the spring they rise up to the surface again and begin to grow.

IN a very large number of cases the diffusion of seeds is effected by animals. To this class belong the fruits and berries. In them an outer fleshy portion becomes pulpy, and generally sweet, inclosing the seeds. It is remarkable that such fruits, in order, doubtless, to attract animals, are, like flowers, brightly coloured-as, for instance, the Cherry, Currant, Apple, Peach, Plum, Strawberry, Raspberry, and many others. This colour, moreover, is not present in the unripe fruit, but is rapidly developed at maturity. In such cases the actual seed is generally protected by a