THE ENEMIES OF ENGLISH WOODLANDS 291 



Marshall Ward in Timber and some of its Diseases. As 

 this account of it is generally accepted as correct by all 

 competent authorities, it may be briefly given in detail 

 here. 



The spores of the fungus germinate in the presence of 

 moisture, but only infect a healthy tree through a wound. 

 From this wound the mycelium spreads in the soft bast, 

 partly between and partly in the cells, and killing and 

 browning the tissues. In summer the growth of the 

 mycelium ceases, and an unusually broad layer of cork is 

 formed between the sound and diseased tissues. In autumn 

 the mycelium again succeeds in entering the living bast by 

 piercing this cork layer, and continues its growth until the 

 following spring in the wood and bast. This is, briefly, the 

 course of events which is continually going on in every 

 larch blister on an infected tree, and there is no reason to 

 doubt the accuracy of Hartig's conclusions as regards the 

 life-history of the parasite after it has once gained a 

 footing. 



In 1891 a valuable paper by Dr. Carruthers on the 

 disease was published in the Journal of the Eoyal Agri- 

 cultural Society. Dr. Carruthers considered that the disease 

 was most prevalent in crowded plantations, while, on the 

 other hand, open woods and especially single trees in mixed 

 plantations are less subject to attack. Dr. Carruthers also 

 stated that the spores could germinate on unwounded bark, 

 providing that it were not more than four or five years old, 

 and his only remedy, beyond favourable cultural conditions, 

 was that of excising the blister and dressing the wound. 



In 1893 the English Agricultural Society sent out 

 circulars to a number of its members, containing a list of 

 questions in connection with the disease. The replies to' 

 these were collated by Dr. Somerville as follows : 



(1) The primary cause is a fungus, Peziza Wilkommi ; 



(2) the disease is as prevalent now as it has ever been ; 



(3) the trees are most liable to attack between seven and 

 fifteen years of age ; (4) blisters are most likely to occur near 

 the surface of the ground or at the base of a young branch ; 

 (5) low and damp situations are factors predisposing to 

 disease; (6) trees at high elevations are less subject to 



