62 



CAliDAMINE. 



[chap. 



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. 44). Conse- 

 quently, 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. 



I have mentioned these species because they are 

 some of our commonest wild flowers, so that during 



Fig. 44. — Common Vetch (yicia strjiitim). 

 The line a b shows the direction of the woody fibres. 



the summer and autumn we may in almost any walk 

 observe for ourselves this innocent artillery. There 

 are, however, many other more or less similar cases. 

 Thus the Squirting Cucumber {Momordica elateriuni), 

 a common plant in the south of Europe, and one 

 grown in some places for medicinal purposes, effects 

 the same object by a totally different mechanism. 



