THE ENEMIES OF ENGLISH WOODLANDS 289 



can easily be understood that a very slight weakness on the 

 part of the host may convert a harmless saprophyte into a 

 dangerous parasite at any time, and it is often an open 

 question whether the bad health of a tree is the cause or 

 the effect of fungoid attack. 



Amongst the fungoid pests which come within the range 

 of practical forestry, not more than half a dozen can be 

 considered of serious importance. These may be summed 

 up as follows : " The Larch Disease " (P. Wilkommi), the 

 "Heart-Eot," the "Honey Fungus" (Agaricus melkus), 

 Trametes radiciperda, the "Beech and the Ash Canker" 

 (Nectria ditissima), and one or two others, such as Hysterium 

 pinastri, Peridermium pini on Scots fir, Peronospora on beech 

 seedlings, etc. As in the case of insect pests, there are 

 dozens of others which might be included in a formidable 

 catalogue, but, under ordinary circumstances, they are com- 

 paratively harmless, or their presence is, as already said, 

 as much the result of bad health in the host as the cause 

 of it. The most serious, from a general point of view, is 

 considered the 



LAKCH BLISTER DISEASE. 



To describe the larch blister to practical foresters is 

 almost superfluous. Everyone knows its characteristic 

 appearance in the stem and branches of trees of all ages, 

 and most foresters have a pet theory of their own to account 

 for it. Some say it is frost in late spring, others that the 

 weight of snow on the branches is responsible for it, another 

 will put it down to deteriorated constitution arising from 

 home-saved seed, while the majority of young and up-to- 

 date members of the profession get Hartig's definition of 

 it off by heart, and repeat it whenever they get the 

 opportunity. 



Eminent mycologists have studied it, and all differ over 

 some one or other of its numerous peculiarities and methods 

 of attack. One believes that it can only enter by a wound, 

 while another states that wounds are unnecessary. By a 

 third it is said to be indirectly due to the attacks of the 

 larch aphis. In fact, one theory has been taken up after 

 19 



