MOVEMENTS OF SEEDLINGS. 37 



the first change is the protrusion of the radicle, 

 which immediately bends downwards and endeav- 

 ors to penetrate the ground. In order to effect 

 this, it is almost necessary that the seed should 

 be pressed down so as to offer some resistance, 

 unless indeed the soil is extremely loose ; for 

 otherwise the seed is lifted up, instead of the radi- 

 cle penetrating the surface. But seeds often get 

 covered by earth thrown up by burrowing quad- 

 rupeds or scratching birds, by the castings of 

 earthworms, by heaps of excrement, the decaying 

 branches of trees, etc., and will thus be pressed 

 down ; and they must often fall into cracks when 

 the ground is dry, or into holes. Even with seeds 

 lying on the bare surface, the first developed root- 

 hairs, by becoming attached to stones or other 

 objects on the surface, are able to hold down the 

 upper part of the radicle, whilst the tip penetrates 

 the ground. . ." l This is well seen in the germina- 

 tion of Clover. 



" The tip of the radicle, as soon as it protrudes 

 from the seed-coats, begins to circumnutate, and 

 the whole growing part continues to do so, prob- 

 ably for as long as growth continues. ..." 



Then conies into play the action of gravitation, 



1 p. 69. 



