50 PLANT LIFE. 



away from its stalk, and, coiling up as it does so, sends 

 the seed flying to a considerable distance. Lubbock's 

 excellent account of the way in which these and other 

 British plants disperse their seeds should be consulted. 

 The catapult arrangement found in many Labiatae, 

 depends upon the stalks or pedicels of the separate 

 flowers ; when these are bent down they suddenly 

 spring up, and the nutlet is thrown out of the calyx 

 and carried to a considerable distance. Sometimes a 

 circle of hairs in the calyx acts like the rifling of a gun, 

 and gives the seed a turning motion as it starts. But, 

 perhaps, the most remarkable case of all is that of the 

 Woodsorrel, which has a little cup-like covering to its 

 seed, really an aril or supplementary seed-coat. This is 

 highly elastic, and when drying suddenly turns inside 

 out, jerking the seed a long way ofl' from the parent 

 plant 



In many grasses, and in the Storksbill, the hygro- 

 scopic property of certain thin dry tissues of the bracts 

 or carpels by which they twist or untwist as the air 

 changes from wet to dry is utilised in a most remark- 

 able way in the dispersal of seed. Avena sterilis, Lagurus 

 ovatus, and several species of Stipa, are good examples. 

 In these one of the bracts enclosing the fruit possesses an 

 extremely long spine or awn^ which is abruptly bent at 

 an angle. If put in a tumbler of water this awn slowly 

 moves until it is quite straight. If it is then held 

 near a candle or heated surface it dries, and suddenly 

 whirls round and round, curling into a corkscrew spiral 

 at the bend. 



If one examines the part which contains the seed it 

 will be found that it ends at the base in a sharp and 

 very hard tip, whilst further back there are stiff and 

 rigid hairs pointing upwards. 



