HEART-WOOD ROT 193 



access to living tissues through a wound. The heart-wood 

 is first attacked, the trunk eventually becoming hollow, 

 but frequently continuing to live for some years, until the 

 outermost and youngest layers of wood are destroyed. 

 The disorganised heart-wood is of a yellowish-white colour, 

 and very soft, and there is a narrow band of a dark brown 

 colour, which indicates the outward point of progress of 

 the mycelium, which is most vigorous in the region of this 

 band of colour, and pushing thence into the younger, still 

 sound wood. 



Preventive Means. — Same as for other species of 

 Polyporus. 



Prillieux, Malad. des Plantes Agric, vol. i. p. 352. 



HEART-WOOD ROT 



{Polyporus sulphureus^ Fries.) 



This showy fungus is not uncommon as a parasite on 

 the trunk of various trees, as oak, alder, willow, poplar, 

 pear, apple, Robinia, and larch. When quite young it is a 

 roundish, fleshy knob, which grows into an irregularly 

 flattened body, the margin being often crisped or wavy, 

 and bearing the very short, minute pores or hymenium on 

 its under surface. In vigorous specimens there are several 

 such overlapping portions or pilei, the whole frequently 

 weighing several pounds, and measuring six inches to a 

 foot across, or sometimes even much more. The upper 

 surface is smooth, and varies in colour from pale yellow to 

 orange, becoming bleached and pale when old. The 

 under surface is bright sulphur-yellow. The flesh is white, 



N 



