I] NATURAL HISTORY OF THE SOIL 11 



foods, and unstable organic compounds rich in stores 

 of easily liberated energy, while the pores contain air 

 and a considerable amount of water. 



Into the pores of this mass we have no means of 

 penetrating : no microscope has been devised that 

 enables us to look into it and see what is going on. 

 We have indirect but incontrovertible evidence, how- 

 ever, that it is full of life and that the soil is inhabited 

 by myriads of organisms of very varied kind, some of 

 which, like eel-worms, are easily visible with a small 

 microscope, while others, like bacteria, require a high 

 power to reveal their presence. They bring about 

 decay, and thus clear away the residues of previous 

 plants leaving the soil clear for a new race. They do 

 even more : they make the old plant material into 

 new plant food. There are signs of conflicting and 

 competing groups of organisms, but all at any rate 

 have this in common : that they are dependent abso- 

 lutely and entirely on the organic matter of the soil. 



In its main outlines this conception of the soil 

 is probably correct, and every month adds to our 

 knowledge of the details. But the picture is still 

 far from complete and it does not enable us to 

 explain all the facts about the soil that have been 

 gleaned by good farmers and gardeners. Each im- 

 portant discovery that is made opens out a wider 

 field for exploration, and we may be certain that we 

 never shall know all about the soil. 



