114 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



by root fungi, then we shall be able to frame measures to cope 

 with the latter. 



It is interesting to note that Fames annosus seldom, if ever, 

 attacks living and healthy hardwoods, even when grown along 

 with badly damaged conifers under similar conditions. This 

 seems to point to some special protective tissue in the roots 

 of hardwoods, resisting the destructive agency in the soil, which 

 so acts upon the roots of conifers as to render them open to 

 attack. 



I venture to suggest that this injurious factor in the soil 

 is acidity or sourness which may be due to several causes, 

 and that the ferments or enzymes of the fungus are unable 

 to attack the roots of conifers unless these have first been 

 weakened by soil acids. The roots of hardwoods are so well 

 protected that the combined action of both acid and ferment 

 does not destroy them. Most Scottish soils are acidic by nature, 

 but there are degrees of acidity, and some coniferous species 

 appear to resist the action of acids better than others. Of the 

 numerous woods in which I have encountered heart-rot, I can 

 remember none in which the presence of the fungus could not 

 be explained by excess of soil acids, either due to the nature 

 of the soil or to an over-accumulation of humus. 



There are other facts which seem to support this conten- 

 tion : — 



1. Fomes annosus is very common all over the country where 



a second crop of conifers follows a first, especially 

 where the soil is of an impermeable nature. This may 

 be due to the humus of the first crop being un- 

 decomposed and rendering the soil sour. 



2. Heart-rot is frequent in first plantations on old agricultural 



ground. On such ground the subsoil drainage 

 conditions are usually very bad, tending to acidity 

 in the upper layer. 



3. Hardwoods replace conifers naturally on the Boulder tills 



all over the country. These clays, owing to poor 

 drainage, are usually of an acid nature. Spruce and 

 larch are confined naturally to well-drained soils formed 

 from the decay of rock " in situ " where the easily 

 soluble bases are most concentrated. These species 

 are always at their best in this country on similar 

 types of soil. 



