R. J. Tabor and Kate Barratt 25 



of the fungus, it may be concluded that there is little danger of the 

 fungus establishing itself by chance infection of spores on young, vigor- 

 ous maiden trees. The success of the inoculations on the pollard can 

 probably be ascribed to the impaired vitality of these trees, and the 

 consequent lowering of the power of the living tissues to resist attack. 

 The fungus established on a dead area of bark can thus invade the 

 neighbouring living tissues, it develops rapidly in the inner bark and 

 attacks the cambium and the superficial layers of the wood. It may 

 be as well to emphasise the fact that on these beeches at any rate 

 Bulgaria does very little injury to the wood, but is responsible for the 

 death and destruction of the bark. 



Dissemination op the Disease. 



The familiar black apothecia of the fungus appear in early autumn 

 (Fig. 5). They eject their spores in such abundance that the surround- 

 ing bark is covered by a black sooty deposit. The investigations of 

 Tulasne(i) and Brefeld(2) have shown that the spores germinate readily, 

 giving rise to secondary conidia or to mycelia directly according to the 

 conditions of germination. The ascospores thus serve as a ready 

 means for the dissemination of the fungus but by no means the only one. 

 If they establish the mycelium on an exposed wound it is able in the 

 enfeebled trees to extend itself to the living tissues. The principal 

 development of the fungus takes place in the spring and early summer, 

 as is evidenced by the active gumming that goes on at that time. 

 When the bark has been completely permeated by the fungus the 

 latter collects between the outer bark and the thin covering layer of 

 cork, and forms shallow stromata on which are later formed the apo- 

 thecia. Before these appear however, other fructifications are developed 

 on the stroma in the form of numerous pycnidia. These are borne 

 in irregular fructifications which form close beneath the lenticels and 

 usually split the cork at those points. These prominences show in 

 surface view the numerous irregular openings of the pycnidia, from 

 which emerge rounded masses, or fine tendrils of black paste, which 

 make their appearance on the surface of the bark, hardening on exposure 

 to the air but readily dispersing when moistened with water (Figs. 4 

 and 5). 



This paste consists entirely of the pycnoconidia (stylospores) 

 described by Tulasne(i). They bear, both in size and form, a strong 

 resemblance to the ascospores and behave in a precisely similar way on 

 germination. In all the material examined at the right season these 



