CHAP. Xn. GENERAL RESULTS. 453 



inorganic matter. We know from the admirable 

 researches of Messrs. Lawes and Gilbert* that different 

 plants require and consume very different amounts of 

 inorganic matter. But the amount in the soil would 

 probably not make so great a difference to the several 

 individuals of any particular species as might at first 

 be expected ; for the surrounding species with 

 different requirements would tend, from existing in 

 greater or lesser numbers, to keep each species in a 

 sort of equilibrium, with respect to what it could obtain 

 from the soil. So it would be even with respect to 

 moisture during dry seasons ; and how powerful is the 

 influence of a little more or less moisture in the soil 

 on the presence and distribution of plants, is often 

 well shown in old pasture fields which still retain 

 traces of former ridges and furrows. Nevertheless, as 

 the proportional numbers of the surrounding plants in 

 two neighbouring places is rarely exactly the same, the 

 individuals of the same species will be subjected to 

 somewhat different conditions with respect to what they 

 can absorb from the soil. It is surprising how the free 

 growth of one set of plants affects others growing 

 mingled with them ; I allowed the plants on rather 

 more than a square yard of turf which had been closely 

 mown for several years, to grow up ; and nine species 

 out of twenty were thus exterminated; but whether 

 this was altogether due to the kinds which grew up 

 robbing the others of nutriment, I do not know. 



Seeds often lie dormant for several years in the 

 ground, and germinate when brought near the surface 

 by any means, as by burrowing animals. They would 

 probably be affected by the mere circumstance of having 



* ' Journal of the Royal Agricultural Soc. of England,' voL xxir, 

 part i. 



