THE HONEY FUNGUS 161 



covered by resin, they are only open to infection for a very 

 short period. 



Evidence from observation confirms the deduction that 

 infection by spores is unusual, for when attacked trees are 

 rooted up it is almost always found that the soil in their 

 vicinity is infested with rhizomorphs, which can generally 

 be traced to a neighbouring stump. In such cases the 

 evidence for infection by rhizomorphs as against infection 

 by spores is overwhelming. 



What then is the use of spores ? Spores are the common 

 means by which the fungus attacks dead, but uninfected, 

 stumps. As will be shown later, a stump is employed as 

 a base from which the fungus attacks living trees, so that 

 spores are the medium by which it forms new bases from 

 which the fungus proceeds on a career of penetration in 

 limited tracts of forest. 



Infection by rhizomorphs, on the other hand, is a matter 

 of common observation, and it is no doubt the general 

 means employed by the fungus in attacking living trees. It 

 is through the rootstocks or larger roots that the rhizo- 

 morphs enter, but it is still a question whether an entrance 

 is effected (i) through healthy, uninjured bark, (ii) through 

 wounds, or (iii) through dead roots. 



Most of the experimental evidence bearing on the subject 

 of infection by rhizomorphs is concerned with, broad-leaved 

 trees. Hartig (1894 and 1901) experimented on the oak 

 and Cieslar (1896) used a variety of dicotyledons. Wagner 

 (1899) planted 43 small trees of various broad-leaved species 

 in a garden in which the soil was infected with rhizomorphs. 

 Of these, 17 had been intentionally wounded on roots or 

 rootstocks. Eight of the wounded trees became infected 

 and none of the unwounded. This result is in general 

 agreement with the conclusions of the other authors. 



A better known experiment of Bref eld's, designed to 

 show that Rhizomorpha subterranea could give rise to 

 Rh. subcorticalis, should also be mentioned. It was 

 not intended to demonstrate any pathological principle, 

 so that for the present purpose it is of very limited value. 



1888 



