306 ENGLISH ESTATE FORESTRY 



more common disease on sands and chalk than on clay or 

 gravel. On moist, springy ground it rarely proves trouble- 

 some, although a certain proportion of trees in most planta- 

 tions are affected with it. Eemedy, of course, there is none, 

 beyond the planting of larch on suitable ground, and then 

 we cannot always be wise until after the event. 



As with the blister disease, heart-rot may be caused by 

 a constitutional deterioration of the tree. But, whether this 

 is so or not, there can be little doubt that soil is the greatest 

 factor in inducing or preventing it, and that a fairly moist 

 and porous soil is the one least likely to favour the disease, 

 as is the case, more or less, with blister disease. Thin, dry 

 soils, on the other hand, are particularly subject to it, and 

 on many of these it is a rare thing to meet with a really 

 aound tree after the twentieth year or so after planting. 

 On dry soils lack of moisture also aggravates the evil, 

 by rendering the surface strata more or less incapable of 

 supporting growth, and the roots have no alternative but to 

 descend. 



Certain geological formations, again, appear to favour 

 the disease more than others. As already said, thin chalky 

 soils rarely grow sound larch, while the oolite, which is very 

 similar to chalk in many respects, produces first-rate larch 

 timber. This may possibly be due to some physical or 

 mechanical difference in the soils of these two formations, 

 which enables the roots to reach water-holding and aerated 

 strata in the one case, but not in the other. The larch is 

 very susceptible to any favourable or adverse conditions of 

 the surface soil, and the development of its surface roots, as 

 already said, is of the first importance, although in exception- 

 ally porous soils they may penetrate to a fair depth. But 

 in a soil which prevents surface rooting, and compels the 

 roots to descend to badly aerated soil below, their normal 

 functions are interfered with, and their vitality decreased. 

 Under such conditions heart-rot becomes more or less general, 

 and must be regarded as a foregone conclusion. 



The immediate cause of heart-rot in the stem is the 

 death and decay of one or more of the main roots, from which 

 the stem is an upward continuation. It may arise in some 

 instances from fractures or injuries sustained by these roots, 



