I I 8 PLANT LIFE. 



to grow. On a very heavy clay soil potatoes can only 

 be grown, if it is very deeply ploughed ; and, in the 

 sanae way, the steep clay bank of a railway cutting will 

 occasionally produce in great abundance plants like 

 Ladies' Fingers {Anthyllis viilnei^arid), and others, which 

 are associated in one's mind with sandy and dry 

 places. In the last case, the slope prevents the 

 accumulation of water characteristic of clay soils, and 

 it becomes very much drier. The ordinary farmer's 

 terms, " cold " and " warm," depend on the same 

 factor. If the soil allows water to trickle through 

 readily, it is drier, and has a higher temperature than 

 ground which is always wet, and evaporating water. 



A character of equal importance is the amount of 

 air channels in the earth by which oxygen can be 

 obtained, both by the roots and by those animals 

 which live amongst them. To keep the roots well 

 supplied with oxygen, and to allow it to work on 

 decaying matter, is, in fact, exactly the office which 

 these creatures perform. The difference between leaf 

 mould, which is extraordinarily fertile, and peat, which 

 is exceedingly barren in its natural state, is largely due 

 to the activity of worms and other animals. These, by 

 burrowing in the soil, ensure a perpetual supply of 

 oxygen to the decaying vegetable matter, which then 

 becomes available for the roots. Otherwise, in wet 

 places peat will be formed ; or, in dry and exposed 

 woods, a blackish brown peat-like mass, on which 

 Blaeberry and Heather begin to grow. In both cases the 

 process of breaking up or decomposing the decaying 

 vegetable matter is hindered, and the absence of worms 

 is one of the most important causes. 



The water contains in solution practically everything 

 which is found in the soil. Of the minerals, only a 



