56 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



8. Polyporus Schweinitzii, Fr.^ 



{With Plate.) 



By J. M. Murray, B.Sc.(Agr.). B.Sc.(For.). 



This fungus has been known on the Continent for many years 

 as an enemy of Scots pine, Weymouth pine and larch, but has 

 not been considered to be a serious enemy. In the United 

 States it is common throughout the northern forests of spruce 

 and fir, and is said to be one of the most destructive of Polypori. 

 There, it is recorded as attacking the white and red spruces, 

 Balsam firs, T/ucJas, and Weymouth pine. In Britain 

 P. Schweinitzii has hitherto been regarded as a rare species. 

 It would seem to be becoming much more common, however, 

 and may yet have to be regarded as a great danger to coniferous 

 forests. I have found it attacking Douglas fir and Sitka spruce 

 in Perthshire, and Scots pine in Midlothian. It has also been 

 recorded on larch in England. 



The fructifications are large and easily recognised (Plate VII.). 

 They appear from July to October and may occur in two forms. 

 When springing from a level surface they are usually circular, 

 plano-concave, and may consist of several tiers supported by 

 a short, stout, central stalk. When springing from an upright 

 matrix the pileus may be almost sessile and bracket-like. On 

 their first appearance the sporophores are soft, cushion-like, 

 and brownish-yellow in colour. When mature they become 

 dark brown and velvety above, with darker and lighter 

 zones alternating so that the pileus has a ringed appearance. 

 The margin is usually greyish, or tawny white for a time, 

 but ultimately the whole becomes dark brown. The interior 

 of each sporophore is warm brown and spongy-fibrous. 



The hymenial layer is greenish-brown and quickly changes 

 to dark red on being bruised. The pores are rather large 

 and irregular in outline. Large white or yellow spores are 

 produced in large numbers on basidia with which are inter- 

 mixed various forms of hairs. 



The presence of the fungus may be indicated first by the 

 appearance of one or more sporophores at a short distance 

 from the tree stem. These arise from a mycelium living on 



' Folyporm viollis, Fr., of R. Hartig in Zersetzungserscheinungen dcs Holzes.; 

 P. mollis, Pers, ; P. sistoiremoides. Alb. et Schw. 



