212 Transactions British Mycological Society. 



explore. It seems probable that the bulk of the living root 

 system in such cases is confined to ground already sheltered by 

 the leaf canopy and consequently deficient in water supply and 

 impoverished in nutritive material. The whole of the area 

 beneath the tree is not short of water; during wet weather water 

 trickles down the bole of the tree and saturates the area in its 

 immediate vicinity: the finer roots doubtless make good use of 

 this supply, and its presence may encourage additional adven- 

 titious roots in this area. This problem requires more experi- 

 mental investigation. Unfortunately the roots of the hollow 

 trees in Richmond Park are not grubbed up, so there has been 

 no opportunity of studying their root systems. Any mycologist 

 able to investigate such root-systems would confer a great boon 

 on his physio-mycological brethren by publishing notes on such 

 examinations : it is with a view to eliciting such assistance that 

 the present observations are published. 



No brackets of Polyporus dryadeus have been found on oaks 

 in Richmond Park but Dr J. W. Munro called my attention to 

 white woolly masses of mycelium in some heart wood which 

 suggested this fungus. Occasionally signs of polypores have 

 been seen but not in a state sufficiently developed for critical 

 determination. Rhizomorphs of what appeared to be Armillaria 

 mellea Vahl. were seen on one or two occasions; and on one 

 dead butt fructifications of Armillaria mellea were found. 



An examination of the root systems of a number of hollow 

 trees — including an Elm hollowed by Fames ulmarius and others 

 by fungi bearing no sporophores — has in every case shown 

 abnormal development of fibrous roots under the leaf canopy 

 and decay among the larger roots. These facts have suggested 

 the following hypothesis as to one of the causes of stag-headed- 

 ness of oaks after weak, parasitic, fungoid infection. If the 

 infection has gained entrance via a branch wound and has 

 assisted in the decay of the heart wood while exploring the 

 less vigorous cells of the living sap-wood, then the mycelium 

 gradually extends first down tlie centre of the trunk and later 

 along the main roots. Following the advance of the fungus the 

 attacked tissues would decay and become hollow. When such 

 hollowness extends right down into the earth penetrating the 

 lower portions of the main root (as it does) then the food in 

 solution conveyed by the vessels in the lower parts of these roots 

 either is wasted or in very small part utihsed by the adjacent 

 healthy cells which are still in direct connection with the xylem 

 strands of the stem. The oak ceases to obtain a large proportion 

 of the liquid nourishment it previously received and suffers in 

 consequence. The phloem stream also would be interfered with 

 and consequently the lower portions of the main roots are least 



