2 BULLETIN 490, U. S. DEPARTMENT OF AGRICULTURE. 



areas are often fan shaped and radiate outward from the center of 

 the log, like spokes from the hub of a wagon wheel, or they may he 

 isolated and occur anywhere in the heartwood. (2) A more ad- 

 vanced, or what might be called an intermediate stage, of the rot, in 

 which the affected heartwood is whitish or grayish in color and is so 

 disintegrated that small pieces can be pulled out. The rotted wood 

 consists of soft white strands of cellulose, intermixed with less rotted 

 wood particles. The rotten wood in this stage is often so w r et and 

 soggy that water can be squeezed out of it. The white-rot or gray- 

 rot stage is usually in the center of the log and is often surrounded 

 by the brownish fanlike areas seen in the first stage of the rot. (3) 

 A third or final stage of the rot, in which much of the heartwood 

 has been destroyed, leaving the remainder in a very brittle, rotten 

 condition, so that it easily crumbles when handled. In this final 

 stage of the rot all of the cellulose has been absorbed by the fungus, 

 while the wood particles left are reddish to dark brown in color. 

 This stage sometimes occupies only a small portion of the heartwood 

 in the center of the log and may be surrounded by one or both of the 

 other stages. 



LONGITUDINAL-SECTION VIEW. 



In a longitudinal section, as seen in sawed lumber, the different 

 stages of the rot gradually merge into one another. In the place 

 where the fungus entered the tree will be found the oldest stage 

 which the rot has reached in that particular lesion. If the entire 

 lesion originated from only one center of infection (one dead branch) 

 and the rot has been in the tree for many years, then the three stages 

 described will probably be represented in the one lesion, which may 

 be anywhere from 12 to 20 feet long. There will usually be some 6 

 to 10 feet in the center of the log which belong to the second and 

 third stages of the rot. while the extremities of the rot lesion will 

 consist of the first stage of the rot. 



DEVELOPMENT OF WESTERN RED-ROT IN THE TREE. 



This rot advances nearly as rapidly radially as it does longitu- 

 dinally in the heartwood of the affected tree. Its radial development 

 in the wood is rather peculiar. From the central cylinder of the rot, 

 at irregular intervals along its entire length, narrow radial patches 

 of rot extend outward toward the sapwood. These radial patches 

 are the fanlike or spokelike discolored areas on the end of the log. 

 described under the first stage of the rot. The centers of these radial 

 patches usually consist of whitish delignified tissue, bordered by red- 

 dish to dark-brown areas of heartwood which have not yet been de- 

 lignifiecl but are in the early stages of the rot. Often some of the 

 cellulose in the center of these patches has been entirely absorbed, 

 leaving small irregular cavities extending to the sapwood. 



