200 DISEASES OF TREES 



POLYPORUS SULPHUREUS l * 



This is one of the most widely distributed parasites of the oak, 

 Robinia, alder, tree-willows, poplars, walnut, and pear. It also 

 occurs as a parasite on the common larch. Infection takes place 

 through a branch-wound, and the mycelium spreads rapidly in 

 the wood, causing it to become red brown and dry. The wood 

 reveals numerous cracks, into which the mycelium grows, to form 

 large sheets of felted hyphae. In the case of dicotyledonous 

 trees the vessels become filled, in the early stages of decom- 

 position, with a dense fungoid growth, so that, on a transverse 

 section, they appear as white spots, and, on a longitudinal section, 

 as white lines. The walls of the elements of the wood become 

 brown and very rich in carbon, and shrink greatly, but on being 

 treated with dilute caustic potash they swell up and become 

 almost completely dissolved. The spiral cracks, which always 

 ascend from right to left in the interior of the fibres, never 

 extend into the middle lamella. 



Whenever old snags, or any kind of wound, admit of the 

 mycelium reaching the surface, a group of sporophores is annually 

 formed. These are succulent, of a pale sulphur-yellow colour 

 beneath, and pale reddish yellow on their upper surface, and by 

 their size and strikingly luminous colour they readily attract 

 attention. The pileus is internally of a white colour and cheesy 

 consistency. The pores reveal a hymenial layer with clavate 

 basidia. The mycelium of this fungus very frequently develops 

 numerous round gonidia in the wood itself, and during my early 

 investigations on this parasite I regarded these as belonging to 

 a different species of fungus. It very frequently happens that 

 before diseased trees are overthrown by storms, their tissues, on 

 one side or other, die as far out as the bark, and the latter, 

 withering, drops off and allows the red-brown decayed wood to 

 fall out from the inside of the tree. Thus it is not impossible that 

 the gonidia may be carried into the air along with the dust of the 

 decayed wood, and so assist in the distribution of the parasite. 



1 R. Hartig, Zersetzungserscheinungen, pp. no et seq. De Seynes, 

 Recherches pour servir a Vhistoire naturelle des vegetaux inferieurs, 1 888. 



* [Very common in this country. I have frequently collected it in Windsor 

 Park and elsewhere. ED.] 



