ON FRUITS AND SEEDS. 



165 



geraniums, and is overcome by them in different ways. In some species, 

 as for instance in Geranium, dissectiim, a short time before the dehis- 

 cence, the seed-chamber places itself at right angles to the pillar (Fig. 

 7, a). The edges then separate, but they are provided with a fringe 

 of hairs, just strong enough to retain the seed in its position, yet suffi- 

 ciently elastic to allow it to escape when the carpels burst away, re- 

 maining attached, however, to the central pillar by their upper ends 

 (Fig. 7, c). 



In the common herb-robert (Fig. 8), and some other species, the 

 arrangement is somewhat different. In the first place, the whole 

 carpel springs away (Fig. 8, b and c). The seed-chamber (Fig. 8, c) 

 detaches itself from the rod of 

 the carpel (Fig. 8, 6), and when 

 the seed is flung away remains 

 attached to it. Under these 

 circumstances it is unnecessary 

 for the chamber to raise itself 

 from the central pillar, to which 

 accordingly it remains close un- 

 til the moment of disruption 

 (Fig. 6, e). The seed-chamber 

 is, moreover, held in place by 

 a short tongue which projects a 

 little way over its base ; while, 

 on the other hand, the lower 

 end of the rod passes for a 

 short distance between the 

 seed -capsule and the central 

 pillar. The seed -capsule has 

 also near its apex a curious tuft 

 of silky hair (Fig. 8, c), the use 

 of which I will not here stop to 

 discuss. As the result of all this complex mechanism, the seeds when 

 ripe are flung to a distance which is surprising when we consider how 

 small the spring is. In their natural habitat it is almost impossible 

 to find the seeds when once thrown. I, therefore, brought some into 

 the house and placed them on my billiard-table. They were thrown 

 from one end completely over the other, in some cases more than 

 twenty feet. 



Some species of vetch, again, and the common broom, throw their 

 seeds, owing to the elasticity of the pods, which, when ripe, open sud* 

 denly 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 (Fig. 9). 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. 



Diagram. Fig. 8. Geranium Robektianum. a, just 

 before throwing the seed ; 6, the red ; c, the seed 

 enclosed in the capsule. 



