CREEPING MECHANISMS. S43 



and how they brush against one another and against the branches of neighbour- 

 ing shrubs as they swing, and thus receive the stimulus necessary to cause them 

 to throw off the fruits. The contact of animals is, however, a more advantageous 

 means of dispersion, inasmuch as the fruits may be left hanging to their coats by 

 the hard styles and the range of distribution be greatly increased thereby. When 

 there is no assistance from animals, and the cast-off fruits simply fall to the ground, 

 the range of projection is not more than 2-3 metres, which is a comparatively small 

 distance from the spot where the fruits were ripened. 



The limitation of the range of dispersion is still more marked in the case of 

 fruits which creep or hop along the ground than in those where the action is that 

 of a sling or of a catapult. The fruits in question have stiff and very hygroscopic 

 bristles projecting on one side from their external coats, and these bristles continually 

 change their position according to the varying state of the environment in respect 



Fig. 461. Creeping and hopping fruits. 

 i^gilopsventricosa. * JSgilops ovata. Crupina vulgaris. 4 W oKum ftottatum 



of moisture, and by so doing propel the fruit or seeds, as the case may be, in a 



definite direction. The awns which project from the glumes of Grasses (eg. J 



crinitus, Secale fragile, and various species of Mgilops; see figs. 461 1 and 



the strong bristles in which the bract-scales of the flowers in Restiace* termma 



(ea. the South African plant, Hypodiscus aristatus), the calyx-bristles and 



pappus-hairs in Scabiouses and Composites (e.g. Gnipina vulgaris, see fig. I 



the divergent calyx-teeth in Papilionaceas (e.g. Triform stelMum, see fig. 4 



constitute structures whereof the different parts alternately approach a 



from one another and so cause a movement resembling that of creeping. 



these cases the hygroscopic structures are furnished with small teeth. te^n 



the teeth are on both sides, sometimes on one 81 de, and sometimes 



