THE ANGIOSPERMAE 



1509 



first becoming detached at the base, roll up instantaneously towards the 

 apex, tearing off the seeds and jerking them outwards. In Geranium a 

 third spring-mechanism is seen (Fig. 1378). In this genus the five one- 

 seeded carpels have long, beak-like prolongations, each of which is a hollow 

 style, firmly united to the others and terminating in one of the five stigmas. 

 The wall of each style contains a heavy strand of sclerenchyma and an outer 

 layer of soft tissue, the dr\'ing of which causes a contractile strain that 

 eventuallv tears away the wall of the ovary from the central placenta. The 

 wall of the style, now released, coils upwards violently, shooting out the 

 seed from the ovary with an action rather like underhand bowling. 



Fig. 1379. — Viola riviniana. A, Fruiting shoot. B, The separated carpel segments with the 

 seeds ready for expulsion. Oxalis acetosella. C, Fruiting shoot. D, Dehiscent capsule 

 with expelled seeds. In this case the outer integument of the seed is under strain. 

 It splits and rolls back suddenly, ejecting the seed in its inner coat. {After Kerner and 

 Oliver.) 



