INSECTS AND DISEASES 1NJUKIOUS TO FOEEST TEEES. 



bark has become in some way injured, such as might be 

 occasioned by the puncture of an insect, by wind, frost, or 

 from many other causes. The spores send down their germ 

 tubes into the cambium, between the bark and the wood, 

 where the moisture and nourishment afforded causes rapid 

 development of the fungus. This soon spreads to the 

 cells of the wood, and the annual layers either entirely cease 

 to grow, or become disorganised and crippled in growth, 

 causing a hollow appearance of the stem at the point of 

 attack. The surrounding bark, by its attempts to heal over 

 the wound, causes a thickened or burly appearance of the 

 trunk, thus imparting to affected trees the cankered, swollen, 

 and distorted look that is so distinguishing a characteristic. 



The disease appears in this country on the larch, both 

 common and Tyrolese, at all stages of growth up to 30 years, 

 but rarely after that age. 



I have examined a plantation of only four years' growth 

 sadly infested by the Peziza, whereas, in other cases, the 

 trees may be fully 20 years old before being attacked. 



Cause. Under what conditions of growth the larch is 

 most susceptible to the Peziza is still a matter of vague un- 

 certainty, but there can be little doubt that an enfeebled 

 constitution, as fully explained in the article on the larch 

 (Trees for Economic Planting), aided by our peculiarly erratic 

 climate, has much to answer for. 



The variableness of our spring weather is, no doubt, one 

 of the predisposing causes of disease, for, although no degree 

 of frost experienced in this country can injure the tree when 

 leafless, yet few are more sensitive when in young foliage. 



Bearing on the subject of the larch disease, I have com- 

 munications from almost every part of the country, and 

 have personally visited and examined many of the worst 

 infested plantations, particularly in England and Wales. 

 Soil, if we exclude peaty, would seem to have little or 

 nothing to do with encouraging the disease, as I have 

 found it equally virulent on dry, sandy, and heavy damp 

 soils, but worse on chalk. Curious enough, the disease is 

 hardly Ttnowiiin the peat hoo-s of Ireland, and there the 

 rainfall is excessive,, while equally strange is it that it 



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