There are a great many cases in which plants possess powers of movement directed to the dissemination of the seed. Some plants even sow their seeds in the ground. 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 six or eight inches high, which comes up of itself abundantly on any vacant spot in kitchen-gardens or shrubberies. 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 violet, 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, the central part of the flower being entirely covered by the sepals, and the whole having a triangular form. When older, they look at first sight like an ordinary seed capsule, so that the bud seems to pass into the capsule without the flower-stage. Some species of Vetch, and the common Broom, throw their seeds, owing to the elasticity of the pods, which, when ripe, open suddenly with a jerk. Each valve of the pod contains a layer of woody cells, which, however, do not pass straight up the pod, but are more or less inclined to its axis. Consequently, when the pod bursts, it does not, as in the case of Cardamine, roll up like a watch-spring, but twists itself more or less like a corkscrew. I have mentioned these species because they are some of the commonest British wild flowers, so that during the summer and autumn we may in almost any walk observe for ourselves this innocent artillery. There are, however, many other more or less similar cases.