72 AGRICULTURE 



over-estimated, at all events, some exceedingly 

 poor grass land throughout the country 

 contains worms in such abundance that at 

 certain seasons of the year the whole surface 

 of the ground is thickly covered by their 

 casts. If land can remain comparatively 

 infertile, notwithstanding a full supply of 

 these animals, it would appear to be reason- 

 able to assume that the fertility of good land 

 is not largely dependent upon their work. 

 Their action consists in opening channels in 

 the soil, which admit air and offer a more 

 easy means of distribution for the roots 

 of plants. One generally finds worms, or 

 indications of their presence, underneath 

 stones, and by gradually removing the soil 

 from beneath such objects, they no doubt 

 have much to do with the fact that stones 

 gradually sink into soil and, in the course of 

 time, become buried altogether. Worms 

 also help to incorporate plant -remains with 

 the soil. At night worms come to the sur- 

 face generally, however, keeping their 

 tails in the burrows from which they have 

 emerged -and lay hold of leaves and other 

 plant-remains, which they drag into the 

 soil. In autumn and winter it will often 

 be found that the stalks (petioles) of such 

 leaves as ash and horse chestnut are standing 



