A still more remarkable instance is afforded by a beautiful South European grass, Stipa pennata (Fig. 21), the structure of which has been described by Vaucher, and more recently, as well as more completely, by Frank Darwin. The actual seed is small, with a sharp point, and stiff, short hairs pointing backward. The posterior end of the seed is produced into a fine twisted corkscrew-like rod, which is followed by a plain cylindrical portion, attached at an angle to the corkscrew, and ending in a long and beautiful feather, the whole being more than a foot in length. The long feather, no doubt, facilitates the dispersion of the seeds by wind; eventually, however, they sink to the ground, which they tend to reach; the seeds being the heaviest portion, point downward. So the seed remains as long as it is dry, but if a shower comes on, or when the dew falls, the spiral unwinds, and if, as is most probable, the surrounding herbage or any other obstacle prevents the feathers from rising, the seed itself is forced down and so driven by degrees into the ground.
I have already mentioned several cases in which plants produce two kinds of seeds, or at least of pods, the one being adapted to burying itself in the ground. Heterocarpism, if I may term it so, or the power of producing two kinds of reproductive bodies, is not confined
Fig. 22.—Seeds of Corydalis heterocarpa. to these species. There is, for instance, a North African species of corydalis (C. heterocarpa of Durieu) which produces two kinds of seed (Fig. 22), one somewhat flattened, short, and broad, with rounded angles; the other elongated, hooked, and shaped like a shepherd's crook with a thickened staff. In this case the hook in the latter form perhaps serves for dispersion.
Our common Thrincia hirta (Fig. 13, b) also possesses, besides the fruits with the well-known feathery crown, others which are destitute of such a provision, and which probably, therefore, are intended to take root at home.
Mr. Drummond, in the volume of "Hooker's Journal of Botany" for 1842, has described a species of Alisimaceæ which has two sorts of seed-vessels; the one produced from large, floating flowers, the other at the end of short, submerged stalks. He does not, however, describe either the seeds or seed-vessels in detail.
Before concluding, I will say a few words as to the very curious forms presented by certain seeds and fruits. The pods of Lotus, for instance, quaintly resemble a bird's foot, even to the toes; whence the specific name of one species, Ornithopodioides; those of Hippocrepis remind one of a horseshoe; those of Trapa bicornis have an absurd resemblance to the skeleton of a bull's head. These likenesses appear to be accidental, but there are some which probably are of use to the
