THE BIOLOGY OF SOIL. 6i 



of soil-water as understood b}- the last generation 

 of agriculturalists. 



But there is another aspect of this question of 

 soil-organisms which has grown in importance of 

 late to such an extent that we are more than ever 

 justified in regarding the biology of soil as far 

 more vital to the interests of the plant than its 

 pnysical or chemical properties. With many of 

 the fungi in the soil the roots of plants have to 

 compete just as plant competes with plant for 

 water, salts, and other food-materials. The toad- 

 stools which are so conspicuous in fields and 

 forests spring from mycelia which ramify in the 

 ground, and are busily breaking down, the remains 

 of other organisms, and just such fungi are known 

 to store up relatively large quantities of salts of 

 potassium and phosphorus the very salts which 

 are so valuable to crops and occur so sparingly in 

 most soils, but which the extensively spread fungus 

 mycelia can gradually accumulate. Some of these 

 fungi, moreover, are more active in their an- 

 tagonism, and actually attack and pierce the 

 roots as destructive parasites, but I pass these by 

 for the present, as they form the subject for 

 further consideration when we come to the diseases 

 of plants. 



It is obvious that the competition of fungi with 

 root-hairs for mineral salts, oxygen, etc., may be 

 at times acute, and it is extremely probable that 

 cases of so-called sterility of soil, where a par- 

 ticular soil is found unsuitable for a crop, may 

 sometimes be due to this over-competition. 



