DISEASES. 229 



seasons, spring frosts, ^c, and indeed any influence 

 that injures the outer coating of the bark. It is most 

 inveterate on wet, cold soils, such as the borderlands 

 of Scotland and the Xorth of England, and all wet, 

 cold, and clayey soils, damp situations, and imperfectly 

 drained ground. The preventive means are early and 

 free thinniug, cutting down and removing all luxuriant 

 herbage that intercepts the air, more thorough drain- 

 age, and strict attention to preserve all the lower side 

 branches vital till the bark is corticated, heart-wood 

 formed, and the roots sufficiently spread to act as food- 

 collectors as well as water-conductors in conjunction 

 with the branches and atmosphere. 



The second form of disease (geound-eot) commences 

 usually deep in the soil, in the roots which first and 

 farthest enter the subsoil. The decay when once com- 

 menced ascends in the cellular longitudinal tissues of 

 the wood, in various forms and difierent degrees, ac- 

 cordincr to acrsrravatincr circumstances. "When the trees 

 are cut down, the disease is shown in its various stages 

 of advancement, — sometimes the wood only slightly dis- 

 coloured, in others soft and spongy, and again in others 

 in soft rotten pieces, resembling partially decomposed 

 sawdust. The causes of this form of disease are various 

 such as water in the subsoil, stimulated early growth 

 by manures, &c. 



Preventive means. — Drainage, avoiding all kinds of 

 manure, keeping the roots near the surface in planting, 

 and abundance of room to promote spread of roots and 

 branches. 



