OAK DISEASES 



249 



quicldy grow larger and form a number of individual or closely 

 over-lapping shelves, from one to several inches wide (Fig. 49). 

 The upper surface of the sheh'es is bright orange-yellow marked 

 with redder areas, while the under 

 surfaces are sulfur-yellow and ap- 

 pear honeycombed. The substance 

 of this mature fruiting-body is 

 tough but very watery. Insects 

 rapidly invade it and through 

 their work and decay caused by 

 bacteria and possibly other fungi, 

 the fruiting-body is quickly de- 

 stroyed. What remains of it soon 

 dries and becomes white and brit- 

 tle. The mycelium in the wood 

 lives from year to year and pro- 

 duces these yellow sporophores 

 annually. The young sporophores, 

 collected before the shelves are 

 fully matured, are among the best 

 of the edible fungi. 



Cause. 



Brown checked wood-rot is 

 caused by the fungus known as 

 Polyporus sulphureus. The spores 

 from the tubes on the under sur- 

 face of the sporophores are wind- 

 blown and infect the exposed 

 heartwood at branch wounds. 

 Certain deposits left by the mycelium of the fungus cause 

 the reddish brown discoloration. For further details con- 

 cerning the life history and control of the wood-rot fungi, 

 see page 64. 



Fig. 49. — Fruiting-bodies of Poly- 

 porus sulphureus on an oak. 



