186 



MANUAL OF TREE DISEASES 



covered with small roundish or sinuous openings. The entire 

 fruiting-body is white or yellowish and soft and spongy. 



Caiise. 



The cuboidal wood-rot of hemlock and spruce is caused 

 by the fungus, Polyporus borealis. The spores from the tubes 

 opening on the imder side of the fruiting-body are blown about 

 by the wind. Infection takes place at wounds. The heart- 



FiG. 28. — Cuboidal wood-rot of hemlock. 



wood may be affected from the top to the base of the tree. 

 The sapwood is decayed and the smaller limbs killed at the top 

 of the tree. For further details concerning the life history and 

 control of wood-rotting fungi, see page 64. 



References 



Atkinson, G. F. Polyporus borealis. In Studies of some shade tree 

 and timber destroying fungi. Cornell Univ. Agr. Exp. Sta. Bui. 

 193: 202-208, figs. 66-63. 1901. 



Hartig, R. Polyporus borealis Fr. In Die Zersetzungserscheinungen 

 des Holzes etc., pp. 54-58, pi. 10. 1878. 



