ROOTS AND THE SOIL. I 27 



has been altered chemically by secretions from certain 

 glands, it is deposited in the form of worm casts upon 

 the surface, and is then distributed by rain through 

 the soil. Charles Darwin estimated that on each acre 

 of land, 10 tons of earth passes annually through the 

 mouths of worms, and is changed into rich and fertile 

 humus. 



The worm is by no means the only inhabitant of 

 the soil ; but it so happens that its- function has been 

 studied by Darwin in a classical work which should be 

 consulted by every observer of nature. There are, 

 however, many other soil inhabitants equally worthy of 

 the same thoroughly close scrutiny. Moles, mice, voles, 

 and shrews assist in keeping the soil full of oxygen ; 

 and there are many varieties of insects and their larvae, 

 as well as woodlice, centipedes, etc., whose function is as 

 yet obscure. A few, such as the cockchafer, wireworm, 

 and June bug, spend at least one summer, and, in the 

 case of the first, no less than four seasons, in devouring 

 the roots of our cultivated plants, retiring to lie up 

 in winter to the deeper parts of the soil. These no 

 doubt have their enemies and parasites. Ants, and in 

 warm countries white ants, also have their part to 

 play. 



Thus there are at least all the following distinct and 

 different populations in the soil : (i) The root and 

 colonising underground stems or rhizomes of the larger 

 plants. (2) The fungus assistants dependent upon and 

 attached to them. (3) The fungus enemies, probably 

 one or more adapted to invade each species. (4) Insect 

 enemies, which in most cases devour indiscriminately any 

 roots and rhizomes that they find. (5) Mice and rats 

 or other animals which also devour roots. (6) Worms 

 which commence the process of turning decay-products 



