VI.] DISEASES DUE TO CERTAIN PARASITES. 171 



attacked by these two parasites, though P. tginarms, 

 at any rate, attacks many other dicotyledonous trees 

 as well. It occasionally happens that an oak is 

 attacked by both of these Polyporei, and their mycelia 



Fig 20 — Vertical section through the wall of one of the po'-es of P sidphureus^ 

 showing the ordinary h} phse {e\ tissue of the fruct fica ion {a and V) and the 

 <ipore bearing end^ (d and abo\ e). (After Hartig ) 



become intermingled in the timber : when this is the 

 case the starch-grams reinain intact in those cells which 

 are invaded simultaneously by the hyphce of both fungi. 

 I have been shown longitudinal radial sections of 



