Oct. IS, 1914 Heart-Rot of Oaks and Poplars 67 



elements of the wood. All, or only the outer rows, of cells of the large 

 medullary rays may be delignified, the middle lamellae dissolved, and the 

 completely delignified cell membranes partially absorbed. 



Isolated areas between the large medullary rays may also be delignified. 

 The cells of some of the medullary rays and of the wood parenchyma 

 often contain starch grains even after the absorption of a portion of the 

 inclosing cell walls. A ferruginous substance is also present in many of 

 the cells of the small medullary rays, in the lumen of the wood fibers, 

 and even in some of the other wood structures. Many of the vessels 

 adjacent to each large medullary ray contain hyaline branching hyphae 

 0.5 to i/t in diameter. The association of the delignified areas with the 

 medullary rays is readily seen in a cross section of the wood where 

 delignification is just beginning, but later in the more advanced stages 

 of the rot this association is not so evident when the delignification of 

 the wood fibers has become general throughout the rotting area. The 

 early absorption of portions of the delignified tissue prevents the forma- 

 tion of long continuous strands of cellulose fibers, although in a tangential 

 view irregular white lines may be seen which consist of fragments of the 

 delignified cells (PI. VIII, fig. 5). In very advanced stages of the rot near 

 the center of the tree white longitudinal lines are seen in a radial view 

 (PI. VIII, fig. 4). These usually consist of remnants of partially absorbed 

 cellulose fibers bound together by strands of white mycelium, which 

 also fill the vessels and the minute cavities left by the absorption of the 

 delignified tissue. 



PIPED ROT IN CHESTNUT OAK 



The rot produced by Polyporus dryophilus in the chestnut oak {Quercus 

 prinus) is slightly different from that in white oak. The diseased wood 

 is hazel in color, with very narrow concentric zones of ivory-yellow 

 cellulose. These zones are adjacent to the large spring vessels of each 

 year and consist of the delignified wood fibers of this tissue. The large 

 vessels in radial-longitudinal view are seen, even under a hand lens, to be 

 filled with cobwebby strands of colorless hyphae. It is in the tissue 

 adjacent to such hyphae-filled vessels where the deUgnification is most 

 pronounced. 



PIPED ROT IN THE WESTERN OAKS 



The rot caused by Polyporus dryophilus in these oaks differs but little 

 from that found in the white oak. The mottled appearance of the rot 

 in its earlier stages is not so pronounced. In the final stage of the rot, 

 after a very large proportion of all the elements is delignified, there is 

 but little apparently sound heartwood. In the older rot in the center 

 of the heartwood the white color by far exceeds the brown, of which 

 there is very little. 



