that a provision is made for the seed falling to the earth, end foremost? Perhaps it gives a better chance of dropping into cracks, or fissures, which, as the plant has large roots, may be particularly advantageous to it. When we magnify a seed, we observe that its upper end has a number of spinous projections, especially on its sides, which point obliquely upwards and outwards. Is it probable, that these are for preventing the seed-down from dragging the seed out of any fissure, in which it may have settled? This may not be improbable, and I find that the slightest force, applied laterally, will break the pillar off from the seed, but that a greater force is necessary to separate it in the longitudinal direction.

The way in which the globular form is given to the head of seeds, I have not seen explained.. It is not done simply by a bending back of the leaflets of the calyx, but by a change of form in the receptacle, or part on which the seeds stand. Examine a vertical section of a dandelion flower at any period before the expansion of the seed-ball, and you will perceive that the part on which the florets, or the seeds, are placed is concave (fig. 10. a). But the section of the same part, when the seeds are expanded,

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receptacle becomes convex, and its margin turns back, so as to give a button-like form to the whole, as at (c). The form of the seedball, therefore, is effected, not by a sensibility in the calyx, but by the convexity assumed by the receptacle.

The calyx, however, does possess a very considerable degree of sensibility, and the dandelion affords a good example of the periodical opening and shutting of flowers. On looking at the button-like receptacle, after the seeds are blown off, we perceive a shallow pit or dimple in its middle; and I think that this is connected with a very beautiful part of the economy of the plant. I have stated, that when the florets have become withered they adhere together,

and at last fall off in one bundle when the down-pillar is near its full growth. Now the growth of the outer series of pillars is more rapid than that of the central ones; and the consequence is, that the withered florets are sooner ready to be disengaged from them: the tubes, too, of the florets dry up sooner than in the centre, so that when the process is nearly completed, the bundle adheres chiefly to the central pillars; these, however, continuing still to lengthen, the bundle is at last pushed from its place and falls off. This accounts for the conical form which the under end of the bundle exhibits, and which we may see, at any time, by picking it off when nearly ready to fall. Fig. 10. (d) represents this; (1) shows the florets twisted and adhering to each other; (2) their tubes or lower parts which rested on the pillars; and (3) those which stood on the pillars of the dimple.

The seeds of dandelion are extremely light, and the rays of the parachute or star of down are very numerous, and when magnified, each is seen to be waved, and also armed with many teeth, or minute spines, directed obliquely towards the point; they are generally alternate but very often in pairs.

sel, the seed-ball is formed exactly in a similar way to that of the dandelion; but in neither is it so clean, because in them there is no provision of a pillar for raising each floret from its seed, and, therefore, we generally find numbers of them intermixed with the seed-down. The twisting of the florets in coltsfoot, however, is still more remarkable than in dandelion (fig. 11. a). In all these plants the stalk is hollow, and in the coltsfoot especially the de

a, the flower of coltsfoot in a withered state. b, a vertical section of the receptacle. c, the same cut off. d, the receptacle entire. e, vertical section of the young flower, showing the receptacle to be concave in that state. f, the ball of seed down, showing the florets of the disc lengthened and intermixed with the down. g, sting of a nettle,

velopment of the receptacle seems more like an inflation by air than an increase of substance (fig. 11. b). This, indeed, is so remarkable, that when it is cut off the top of the stalk, by a transverse section, it resembles a hollow case, the sides of which are so thin as to let the light shine through it (fig. 11. c). Though there is no pillar for the seed-down in coltsfoot, there is a curious provision, which seems to me intended to serve the same purpose. The little tubular or bell-shaped florets which occupy the centre of the flower are very short, but the tube of each continues to grow, so that, at length, when the down-ball is formed, the central florets project as far from the receptacle as those of the ray or margin.

The seed in these plants being formed, is left entirely to the wind for its dissemination; and when the down ball is kept in a house, or free from the wind, not one falls; the stalk withers and hangs down, but the seeds continue to adhere to the receptacle.

Another plant, scarcely less common than the dandelion, is the nettle, three species of which are natives of Great Britain; the Roman nettle, the common nettle, and the small. The first is limited to certain situations, but the other two