SEEDS AND FRUITS. I4I 



similar state of matters exists in some siliquas, where the valves 

 suddenly fly up from below on the slightest touch. A good 

 example of this is a small cruciferous 1 plant with white flowers- 

 the hairy bittercress (Cardamine hirsuta), which grows abundantly 

 in waste places. A hand passed lightly over a patch of these 

 plants, when the fruits are ripe, elicits a brisk discharge of 

 seeds. 



Capsules are adapted in some cases for throwing their seeds to 

 a distance, of which the dog-violet is a very good example. Here 

 the capsule bears three rows of seeds on parietal placentas. When 

 ripe, it splits between these into three valves, which separate widely. 

 The edges of each valve now curl up and press against the seeds, 

 here extremely smooth, with the result that they are shot to some 

 distance, just as an orange pip can be projected from between the 

 finger and thumb. 



Succulent fruits are but rarely adapted for ejecting their seeds, 

 but this is the case with the squirting cucumber, common in South 

 Europe. The ripe fruit is in such a state of tension that the 

 lightest touch separates it from the stalk and causes the contents 

 to squirt out with much force. 



(2.) Water effects the distribution of many seeds, especially 

 such as are enclosed in a covering which is watertight and at 

 the same time light enough to make them float. Experiments 

 have been made on this head, leading to the conclusion that the 

 seeds of about one plant in ten could be floated across a sea 900 

 miles broad and still remain capable of germination. Earth, 

 containing seeds, may also be carried for long distances in the 

 crevices of drift-timber. The cocoa-nut is one of the best examples 

 of a fruit which is safely transported by water for an immense 

 distance without injury. Owing to this it is common on the 

 coral islands of the Pacific. 



(3.) Wind plays a very important part in the dispersal of 

 seeds. These are sometimes suited for this by their small size, 

 as in orchids. Such small seeds are often found in porous 

 capsules, like those of snapdragon and poppy, and in these the 

 pores are situated near the top. The seeds cannot, therefore, 

 fall out, but are shaken out by the wind. Each pore in the 

 poppy capsule is provided with a little flap on the lower side, 

 which is said to move up and close the pore in damp weather. 



Coverings or tufts of hair are often present upon seeds and 

 fruits, materially assisting in their dispersal by wind. The 

 commonest example is found in the " pappus " of many Composites, 

 a sort of crown, representing the calyx, which surmounts the 



1 With cross-shaped corolla (0/. Appendix A), a characteristic of the group 

 Cruciferse, of which wallflower and stock are typical examples. 



