COLONIZATION 333 



lengthens. But the spreading hairs catch against the 

 herbage with which they are in contact and resist 

 the lengthening movement. Thus the lengthening of 

 the style, owing to the resistance of the hairs, forces 

 the pointed seed into the ground. One might think 

 that with the advent of dry conditions, owing to the 

 resumption of the spiral form by the style, the con- 

 traction would draw the seed out of the soil. But this 

 does not occur, for the seed is provided with short hairs 

 pointing backwards, which act like the barbs of an 

 arrow, and are strong enough to grip the soil and 

 hold the seed in the place it has gained. Whenever 

 the style absorbs moisture the seed is pushed farther 

 into the soil. Ultimately the useful appendage decays, 

 but not before it has served its remarkable purpose. 

 It should be added that the seeds are dispersed by 

 wind, but even when the air is still they literally crawl 

 over the ground, by the coiling and uncoiling of the 

 style, until they come to rest on a site suitable for the 

 operation just described. The humidity of the atmos- 

 phere is sometimes tested by means of Stork' s-bill 

 seeds. When the atmosphere is laden with moisture 

 the styles straighten out; they coil when the air is 

 dry. 



