﻿38 BULLETIN 1128, U. S. DEPARTMENT OF AGRICULTURE. 



from a white-ash longeron with this incipient decay is illustrated in 

 Plate I, right side. 



Apparently mycelium does not occur in the brown discolored wood 

 in advance of the white spots. It would seem that the wood is not 

 weakened until the white spots are found, and the wood with the 

 brown discoloration alone need not be rejected. It is an excellent 

 hint for close scrutiny of an affected piece, however. The incipient 

 decay is somewhat obscured in rough lumber, but is usually readily 

 apparent on smooth surfaces. This stage does not extend many feet 

 beyond the typical decay, and on long boards the latter will most 

 likely also occur. Once the presence of the typical decay is ascer- 

 tained it is a relatively simple matter to determine the limits of the 

 incipient stage. 



Areas in which the wood failed to change color upon transition 

 from heartwood to sapwood (see p. 16) can be differentiated from 

 the initial stages of white-rot by their larger size, by the straw-yel- 

 low color as opposed to the whitish of the decay, by the sharp line 

 between the two colors, and by the fact that the spots are much 

 larger, without becoming soft and spongy, than would be the case 

 with the decay. 



Sweet birch and yellow birch are subject to a white heart-rot (SB) 

 which, although very- similar to the foregoing, is caused by a dif- 

 ferent fungus, the false tinder fungus (Fomes igniarius (L.) Gill.). 

 The first indication of the incipient decay is a brown discoloration, 

 not very apparent against the reddish brown heartwood. Next, 

 faintly paler streaks or. spots appear, which finally become a yel- 

 lowish white, strikingly apparent against the dark background. 

 This stage is illustrated by Plate VII. In the center of these streaks 

 small spots are found in which the yellowish white wood appears 

 to have collapsed. Usually the long axis of these spots is parallel to 

 the grain, but in some it may be at right angles to it. The wood up 

 to this time appears firm and hard. Next the white streaks merge, 

 the wood becomes soft, and finally the entire affected portion of the 

 heartwood is reduced to a yellowish white fibrous mass composed 

 principally of cellulose, the result of the delignification by the fun- 

 gous hyphse. As in the white-rot of ash, hyphse are not found in the 

 brown discoloration. Hence, no reduction in the strength of the 

 wood may be expected until the very first indications of the whitish 

 streaks or spot, which may be found as much as 8 feet in advance 

 of the typical decay. 



One of the most common decays (&4) on oaks and also on cer- 

 tain poplars (Populus) is the heart-rot caused by the oak fungus 

 (Polyporus drj/ophilvs Berk.). The incipient decay of this whitish 

 piped rot in white oak has a water-soaked appearance in the unsea- 

 soned wood, but when dry the discoloration becomes hazel to tawny 

 in color. The discoloration may extend from 1 to 10 feet in advance 

 of any other indication of the decay. The next stage of the decay, 

 which is best seen on a radial face, is characterized by whitish spots 

 or streaks, usually following the medullary rays, which produce a 

 mottled appearance of the wood. This mottling is the result of a 

 delignification process: that is, the lignin is removed from the wood, 

 leaving only the cellulose. In the final stages the decayed wood is 

 firm, with a white, stringy appearance, and the delignification is 

 practically complete. 



