Page:Popular Science Monthly Volume 19.djvu/173

Rh In other cases the plant throws its own seeds to some little distance. This is the case with the common Cardamine hirsuta, a little plant, I do not like to call it a weed, six or eight inches high, which comes up of itself abundantly on any vacant spot in our kitchen-gardens or shrubberies, and which much resembles that represented in Fig. 17, but without the subterranean pods b. The seeds are contained in a pod which consists of three parts, a central membrane, and two lateral walls. When the pod is ripe the walls are in a state of tension. The seeds are loosely attached to the central piece by short stalks. Now, when the proper moment has arrived, the outer walls are kept in place by a delicate membrane, only just strong enough to resist the tension. The least touch, for instance a puff of wind blowing the plant against a neighbor, detaches the outer wall, which suddenly rolls itself up, generally with such force as to fly from the plant, thus jerking the seeds to a distance of several feet.

In the common violets, besides the colored flowers, there are others in which the corolla is either absent or imperfectly developed. The stamens also are small, but contain pollen, though less than in the colored flowers. In the autumn large numbers of these curious flowers are produced. When very young they look like an ordinary flower-bud (Figs. 2 and 3, a), the central part of the flower being entirely covered by the sepals, and the whole having a triangular form. When older (Figs. 2 and 3, b) they look at first sight like an ordinary seed-capsule, so that the bud seems to pass into the capsule without the flower-stage. The pansy violets do not possess these interesting flowers. In the sweet-violet (Viola odorata and Viola hirta, Fig. 2) they may easily be found by searching among the leaves nestling close to the ground. It is often said, for instance by Vaucher, that the plants actually force these capsules into the ground, and thus sow their own seeds. I have not, however, found this to be the case, though, as the stalk elongates, and the point of the capsule turns downward, if the earth be loose and uneven, it will no doubt sometimes so happen.