DISPERSAL OF FRUITS AND SEEDS 227 



(a) This is well observed in pods of Gorse, Broom, and 

 Sweet-Pea (Fig. 162, 1) ; (5) the two valves of the siliquas 

 of Crucifers, like Bitter Cress (2), split apart suddenly from 

 below upwards ; (c) in Violets (3) the capsule splits into 

 three valves ; then the edge of each closes over and presses 

 on the smooth pear-shaped seeds, which are then forcibly 

 ejected ; (d) in the Geranium (4) the five carpels separate 

 from below upwards, press against the calyx, and eventually 



Fig. 162. Explosive Fruits. 1, pod of Sweet-Pea ; 2, siliqua 

 of Bitter Cress; 3, capsule of Violet; 4, fruit of Geranium; 5, 

 hygroscopic fruit of Crane's-bill ; 6, twisted awn of Oat ; 7, capsule 

 of Wood Sorrel ; 8, Balsam or Touch-me-not. 



gain sufficient force to spring away and throw out the seed 

 as from a sling ; (e) the Crane's-bills (5) split similarly; but 

 the long awn twists spirally and is jerked off, still retaining 

 the seed. This is buried by the movements of the awn, 

 which untwists when moist and coils up again when dry ; 

 (/) the awns of some Grasses act in a similar way (6). But 

 awns may straighten suddenly and jerk the grain some little 

 distance. Stiff hairs on the fruit-coat serve as anchors, 

 preventing the fruit from being drawn upwards from the 

 soil. Plants of this kind are able to bury their own seeds. 



p 2 



