SNAPPING FRUITS 57 
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 Leguminosz. 
In the Cranesbills (Geranium) a very ingenious cata- 
pult 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 hand- 
guard 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 
