THE ENEMIES OF ENGLISH WOODLANDS 295 



attempt is made to connect the prevalence of blister with 

 that of injury by spring frosts, difficulties at once present 

 themselves. As already said, spring frosts do most damage 

 in hollows and low flat ground, where the air tends to stagnate 

 during a frosty night. Larch growing in such spots ought, 

 therefore, if the frost theory is to hold good, to be the most 

 affected by disease, but, as a matter of fact, it is not. We 

 find larch blistered as badly as it can be blistered on slopes 

 and at elevations of 500 or 600 feet above sea-level, 

 and we can also find it fairly free from disease at the 

 bottoms of valleys, and in exactly those spots where the frost 

 ought to damage it most. We do not assert for a moment 

 that trees growing in frosty hollows are more free from 

 disease than those on high ground, but we do assert that the 

 one is just as likely to escape as the other, and therefore 

 some other cause than frost alone must account for the 

 disease when it occurs, and the absence of frosts cannot be 

 credited with its non-appearance. 



Then, again, the theory that snow, by bending down and 

 straining the branches near their junction with the stem, 

 tends to fracture their resin ducts, allows the contents to 

 escape, and thus gives rise to a blister without the co-opera- 

 tion of the fungus, requires a good deal of additional proof. 

 Possibly snow does act in this way in some districts in the 

 north, where wet snow is as frequent an occurrence as rain is 

 in others. But when the fact is considered that wet snow, 

 which accumulates on the branches of trees in this way, is 

 neither an ordinary nor an annual occurrence in many 

 southern districts in which blister is as much a scourge as it 

 is anywhere, then the theory falls to pieces. But, apart from 

 climatic conditions, the position of blisters on most stems and 

 branches does not bear out this theory. If blisters only 

 occurred near the base of a branch, and at the point at which 

 the greatest strain would be experienced, then we might 

 entertain such a theory until something better turned up. 

 But, as a matter of fact, blisters originate and develop on 

 parts of the stems and branches at which no strain of this 

 description could possibly occur. We find it in parts of the 

 stem more or less distant from branches, and it occurs on the 

 latter at their extremities as often as near their base, and 



