SECTION III 

 DISEASES DUE TO CONDITIONS OF SOIL 



SINCE science has recognized that the occurrence of all 

 infectious diseases is perfectly independent of the chemical 

 composition of the soil, that section of plant-pathology which 

 deals with diseases induced by peculiarities of soil has been 

 greatly restricted in extent. 



SOIL IN RELATION TO WATER AND PLANT-FOOD. 



The supply of water and food-materials in the soil has a great 

 influence on the rate of growth of a plant, although it is only 

 in rare instances that it produces disease, in the restricted sense 

 of the term explained at page 5. 



One such form of disease is the condition where the tree is 

 said to become " stagheaded " or 4< top-dry," * and which is usually 

 to be traced to considerable diminution of the supplies of water 

 or food-materials in the soil, and this prevents sufficient nourish- 

 ment being continued to plants that have grown up under more 

 favourable conditions. 



In beech woods this disease is specially liable to occur, in 

 consequence of the removal of litter, and often appears as early 

 as the pole-wood stage. The reduction in soil-fertility first 

 makes itself noticeable in a general diminution of the rate of 

 growth, though frequently also in the withering of the upper 

 portion of the crowns, while the lower portion remains green. 



In alder woods top-drought follows excessive draining. 

 When oaks that have grown up in a dense wood of beeches, 



* [z'.e.y the topmost branches become completely leafless, and die off, and 

 remain as dry sticks, like antlers projecting above the foliage. ED.] 



