VI ] POL YPORUS SULPHURE US. 169 



acorns, embedded in and hollowed out by the mycelium 

 of Polyporus sulphuretis, Hartig's ingenious explana- 

 tion of their presence speaks for itself. A squirrel 

 had stored up the acorns in a hollow in the timber, 

 and had not returned to them — what tragedy inter- 

 venes must be left to the imagination. The Polyporus 

 had then invaded the hollow, and the acorns, and had 

 dissolved and destroyed the cellular and starchy 

 contents of the latter, leaving only the cuticularized 

 and corky shells, looking exactly like fossil eggs in 

 the matrix. I hardly think geology can beat this for 

 a suggestive story. 



The three diseases so far described serve very well 

 as types of a number of others known to be due to 

 the invasion of timber and the dissolution of the walls 

 of its cells, fibres, and vessels by Hymenomycetous 

 fungi, i.e, by fungi allied to the toadstools and pol}'- 

 pores. They all " rot " the timber by destroying its 

 structure and substance, starting from the cambium 

 and medullar}'^ rays. 



To mention one or two additional forms, Trmmtes 

 Pini is common on pines, but, unlike its truly parasitic 

 ally, Tr. radiciperda^ which attacks sound roots, it is 

 a wound-parasite, and seems able to gain access to 

 the timber only if the spores germinate on exposed 

 surfaces. The disease it produces is very like that 



