But the assistance which the parent plant gives is often of a more active and even dramatic character, though in these cases it is usually effected not by a movement of living tissue as in the last case, but by mechanical changes taking place in tissues already dead or dying. If we stand by a bank of Gorse (_Ulex_) on a warm day we may become aware of a snapping sound, and may possibly feel on our faces the impact of small bodies. These are gorse seeds in process of being distributed by the parent. In this shrub the fragrant flowers are succeeded by short tough, hairy pods, formed of two valves joined together by their edges. (In reality the pod is a modified leaf folded down the middle, the two edges thus brought together being joined--see p. 129.) When the seed is ripe the pod dries, and owing to unequal shrinkage of the valves stresses are set up which at last tear the pod suddenly asunder along its edges, flinging the seeds violently out into new ground, where they will have a better chance of life than if merely dropped into the middle of the parent bush. A similar arrangement is found in the Vetches and many other Leguminosæ. In the Cranesbills (_Geranium_) a very ingenious catapult device may be examined. The fruit is of peculiar structure. We might make a rough model of it by taking five single-sticks and tying them to a broom-handle--firmly at the points, less securely elsewhere--and slipping a tennis-ball into each basketwork handguard before turning its open side in against the broom-stick, so that the ball cannot fall out. Imagine now that unequal drying on the part of the sticks tends to make each bend into a semicircular form, which is hindered by the fastenings at either end. The stress will eventually tear the weak fastenings at the base: the lower end will fly up, bearing with it the ball (representing the seed), which will be projected [Illustration: FIG. 9.--FRUIT OF GERANIUM. _a_, Mature; _b_, ditto, with pouches raised ready to discharge nuts; _c_, in act of discharging.]