LARCH-BLISTER. 457 



disease spreads most rapidly in plains and valleys and among 

 low hills. Trees ten to twenty years old suffer most, but the 

 attack is rare in the case of trees more than forty years old. 

 Dense stocking does not suit the larch, and assists in spreading 

 the disease ; sowings therefore suffer more than plantations, 

 and pure woods more than mixed woods. Larches growing 

 with broadleaved trees are least liable to canker. Mr. Michie, 

 in his book on larch (Blackwood & Sons, 1885), says, that 

 after the first fifteen years tree-parts are safe from attack. 

 Hence, in a larch tree, 30 years old, and 45 feet high, the first 

 twenty feet or so are safe. 



The disease originated in the Alps, and when during the 

 first twenty years of this century extensive larch 'plantations 

 were made all over Northern Europe they escaped the disease, 

 even when on inferior soils, but spores of the fungus probably 

 found their way down with larch seed from the Alps, and 

 the disease became widespread in more recent plantations. 

 In the Alps, it is usually confined to individual trees, and 

 does not ruin whole woods as in Germany, Denmark, and 

 Britain. 



The reason is, that, in the Alps, there is a sudden change 

 from winter to quite warm weather, so that the needles develop 

 rapidly, whilst at lower elevations the soil becomes heated at 

 the end of March, and the larch needles then appear, but are 

 subjected to the treacherous spring weather, and do not harden 

 till the beginning of May. During this prolonged period of 

 development of the needles they are liable to attacks of Coleo- 

 vhora laricella, Hbn., and of Chcrmes, which promote the 

 spread of the canker. In the Alps, moreover, the fertile 

 spores are only produced in damp places, near the lakes for 

 instance. 



It should also be remembered that, in its native country, 

 larch has its roots covered by deep snow till May, and that 

 the soil contains plenty of moisture throughout the year, 

 though, owing to the sloping ground on which the larch 

 grows, this moisture is never stagnant. In Britain, then, 

 whenever there is not much winter snow, a moist covering of 

 dead beech leaves, or a deep porous soil resulting from much 

 disintegrated rock, are the best substitutes for Alpine snow. 



