Fistulina hepatica and Stag-headed Oaks 211 



attention was again confined to trees exceeding two feet in 

 diameter, and 60-70 per cent, were found bearing sporophores 

 of Fistulina, many of which were distinctly aged and often green 

 on the top owing to the presence of an Aspergillus sp. The next 

 week only two fresh fructifications could be found in this area, 

 and mau}^ of those previously noted were now rotting away. 

 Practicall}' all the infected trees (only one exception was noticed) 

 had been pollarded, and the original rot — to whatever it was 

 due — presumably had started in the wound. In nearly all 

 cases where the Fistulina was present the trees were stag-headed. 

 Although only preliminar}^ work has been done it is evident 

 that the water content of the soil is not the chief factor in pro- 

 ducing stag-headedness, for trees in the hollows are often more 

 affected than those on higher ground. I think also that Fistulina 

 is more frequent in lower-lpng places. The present general 

 opinion is that stag-headedness in trees is due to an insufficient 

 water-supply. This may, however, be due to various causes, for 

 example, actual lack of water, unavailability of the water, or 

 owing to the wood vessels being insufficient for the requirements 

 of the tree. In the writer's opinion the latter is the primary 

 factor at work in the case of stag-headed oaks. The leaf area 

 has adjusted itself to the supply of water which the vessels 

 were able to supply for average years, and if exceptional causes 

 arise (such as drought) this equilibrium is upset and those 

 portions furthest from the suppl}' suffer most acutely. Fistulina 

 apparently plays a large part in the hollowing of oaks in Rich- 

 mond Park and is possibl}^ also one of the main factors in 

 causing stag-headedness. Observations made by others in other 

 parks and forests would give data of value for the future. 



The following is an instance of the effects of the hollowing upon 

 the root system of an oak. A specimen of Quercus Phcllos, felled 

 at Kew recently as being dangerous, had been hollowed by a 

 polypore. The fungus, however, had not produced fructifica- 

 tion sufficiently well developed for certain identification. In 

 this particular case the root was extracted and showed certain 

 noteworthy features. The internal hollowing extended right 

 down the stem to the soil. The original roots which had supplied 

 the tree for the first few decades had rotted away. The roots 

 which appeared to exist from an observation of the buttresses 

 prior to felling were in fact non-existent and their place had 

 been taken by a number of smaller subsidiary roots which in 

 most cases had arisen from the upper surface of the original 

 buttress root. None of these subsidiary roots exceeded eight 

 inches in diameter. The centre of the tree being rotten or extinct 

 the thin, living shell had developed its own, relatively young 

 root system, which, being small, had a limited range of soil to 



