204 DISEASES OF TREES 



individual elements of the wood become isolated (Fig. 1 26, e /*). 

 It is remarkable that the process of decomposition in the 

 neighbourhood of the cavities undergoes a change when these 

 have become enlarged. The latter no longer appear white but 

 greyish yellow, and reveal abundant felted mycelia, which pierce 

 the walls at numerous places. Instead of a conversion into 



P'lG. 126. Decomposition of oak induced by T. Perdix. a, tracheids containing 

 some filamentous mycelia, and showing a few perforations on their walls ; b, 

 wood-parenchyma containing starch which is partly undergoing solution, the 

 outer granules being the first to disappear ; c, vessels containing hyphae of the 

 fungus ; d, sclerenchymatous fibres containing fungus-filaments, and showing 

 perforations in the walls ; e and /, tracheids which are completely isolated by 

 the solution of the primary wall. The thickened rings of the bordered pits are 

 also seen to be isolated between the tracheids. As the elements are isolated, the 

 cracks no longer cross at the bordered pits, g, cells of wood-parenchyma which 

 are completely isolated and almost completely dissolved ; /i, a tracheid just 

 before final solution ; z, sclerenchymatous fibre much decomposed ; k, a 

 tracheid whose wall has been dismembered by cracks before being dissolved. 



cellulose resulting, the wood-substance is dissolved, partly by the 

 enlargement of the perforations and partly by the centrifugal 

 attenuation of the cell-walls. 



The sporophores of the parasite occur as incrustations in 

 fissures or other cavities in the diseased wood, or on the outside 

 of dead branches. The incrustations, which vary in thickness 

 from -oV- to f inch, are brownish yellow in colour, and consist of 



