294 MANUAL OF TREE DISEASES 



colored rays extending like spokes of a wheel toward the bark. 

 In longitudinal section these rays of decay are seen to have a 

 whitish core of completely decayed tissue. If the wood is 

 split tangentially these rays appear as red elliptical areas with 

 whitish centers. The rays become larger until they finally 

 coalesce. The whitish rotted cores become so completely 

 disorganized that cavities are left which are bordered by white 

 rotted wood. By this manner of . spreading, the fimgus very 

 quickly extends its activities radially, although some time 

 elapses between the pushing out of the rays and the time when, 

 by gradual enlargement, they coalesce. 



The fruiting-bodies of the fungus causing this rot are formed 

 annually on the under sides of logs lying on the ground. They 

 are white and usually resupinate incrusting layers. 



Cause. 



It is thought that the fungus causing the red-ray wood-rot 

 is the same as the one called Polyporus Ellisianus, although this 

 has not been definitely determined. Infection results in old 

 branch wounds at the top of the tree, and the myceliimi spreads 

 upward and downward, often producing a rotted area in the 

 wood twelve to twenty feet long from a single infection. A 

 more detailed discussion of the nature of wood-rots and the life 

 history of the fungi causing them is given on page 64. 



Reference 



Long, W. H. A preliminary report on the occurrence of western red- 

 rot in Pinus ponderosa. U. S. Dept. Agr. Bui. 490 : 1-8. 1917. 



Red-Bkown Root- and Butt-Rot 



Caused by Polyporus Schweinitzii Fries 



This root- and butt-rot occurs in pine, fir, larch, spruce, 

 hemlock and arbor-vitse, wherever these trees grow. The 

 destruction it causes to these conifers is second in importance 



