42 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



An important point about heart-rot is that it is almost 

 invariably confined to certain types of locality, namely, to 

 situations where the soil conditions either favour the growth of 

 the responsible fungi, or inhibit the growth of certain tree 

 species in some way, or where both these conditions are fulfilled. 

 It occurs with most frequency on areas which have been planted 

 a second or third time, and more especially where large stumps 

 of the previous crop, either conifer or hardwood, have been left 

 on the ground. Under these conditions all the common species 

 of conifers succumb to attack, more especially those individuals 

 immediately surrounding the decaying stumps. There is no 

 room for doubt that the decay of these stumps and old roots 

 under the soil is directly responsible in some way for the root 

 fungi attacking the surrounding young trees. There is also 

 good reason to believe that the disease is more prevalent in 

 densely grown young crops, and amongst those species of trees 

 which cast most shade. 



In the natural forest it is the exception and not the rule that 

 the stumps of large dead trees remain under the soil to decay. 

 In most cases the trees are uprooted by storms, and the decay 

 of the trunks and roots takes place above ground in the open 

 air. Under such conditions it is possible that toxic substances 

 formed during decay are further broken up, and do not accumu- 

 late in the soil. It is not unlikely that the process of decay is 

 entirely different to that process taking place under the soil, and 

 that valuable food-material may be provided for growing plants. 

 In commercially exploited forests, or in artificial forests grown for 

 commercial purposes, the usual custom is to cut over the stems 

 at or near the ground level so that the stumps and roots are 

 left to decay " in situ." It is possible that in some soils of an 

 open texture normal decay of the stumps and roots may occur, 

 but it seems highly probable that in less porous soils, and more 

 especially under the shade of a dense young crop, the process of 

 decay becomes abnormal, and each stump eventually produces 

 considerable quantities of harmful substances which adversely 

 affect the roots of the young trees and render them liable to 

 attack by root fungi. It may even be the case that damage to 

 the roots of the young plants during the process of transplanting 

 from the nursery to the field may make these plants more liable 

 to attack, especially in those localities around old stumps where 

 harmful substances abound. On the other hand, natural seed- 



