I INTRODUCTION 17 



which the tiny seeds are jerked out through small 

 holes round the upper edge of the capsule. In many 

 Campanulas the capsule opens by pores at the base 

 of the capsule, which, however, becomes inverted when 

 mature. 



One of the most interesting groups of seeds are those 

 which are thrown by the plants themselves, as, for 

 instance, in the Geraniums, Oxalis, some Violets, Car- 

 damines. Euphorbias, etc. It is remarkable how much 

 in these cases the mechanism differs. 



Some seeds mimic small insects, and are no doubt 

 picked up, and carried some distance before the 

 mistake is discovered, by birds (see, for instance, the 

 Mallows), or even by insects, as in the case of Melam- 

 pyrum. 



A large number of species have very minute seeds. 

 These, of course, have a larger surface in proportion to 

 their weight, and are readily carried by wind without 

 any special provision for the purpose. Arctic and 

 Alpine species very generally belong to this class. 



Many seeds and fruits develop air cavities, which 

 renders them lighter, and thus facilitates dispersal. 

 This is specially the case in water plants, and the seeds 

 are thus enabled to float. 



In the great family of Umbellifers, as a rule, the 

 " carpophore" splits lengthwise, and the two mericarps, 

 each containing a seed, hang loosely by their upper 

 ends to the two whip-like filaments. The dry plants 

 are very elastic, and sway backwards and forwards in 

 the wind, until at last some strong gust tears the 

 mericarps off and carries them away. 



Even when there is no special provision for dispersal, 

 seeds must be often carried about on the feet of animals 

 and the flanks of wallowing quadrupeds. 



Another point to be considered with reference to 

 seeds is the character of the surface. Some are smooth 

 and shining, some reticulate, some pitted. Those with 

 hooks or hairs have already been mentioned. Eeticula- 

 tions often, as, for instance, in Geraniums, fit into 



c 



