Brown : Timber Rot 
7 
of this fungus on chestnut and oak, compared with the condition 
of the normal wood, may now be described.® 
Character of Normal Wood . — The wood of chestnut is of the 
ring-porous type.^- There are several rows of large vessels in 
the spring wood out of which branching rows of smaller vessels 
extend radially into the summer wood. The transition from large 
to small vessels is usually very abrupt (Fig. 6) and the radial 
arrangement of the small vessels is often somewhat obscure. An- 
nual ring formation is pronounced, each ring being sharply de- 
limited from the others. The width of the ring varies within 
wide limits; sometimes in coppice growth it is over half an inch 
in thickness. The pith rays are minute and scarcely distinguish- 
able with the naked eye. 
Miscroscopically the wood of chestnut is seen to consist of (a) 
uniseriate pith rays, (b) pitted vessels, (c) metatracheal paren- 
chyma with simple or semi-bordered pits, (d) tracheids and (e), 
wood fibers. The last are not typical fibers, but of the nature of 
fibrous tracheids.® The vessels are discernible in cross section 
by their size. Fibrous tracheids, tracheids, and wood paren- 
chyma look much alike; the last may be distinguished, however, 
through its protoplasmic contents. The vessels exhibit the greatest 
variation in size in the annual ring. The cell lumina of the paren- 
chyma and prosenchyma are somewhat wider in the spring wood 
than in the summer wood, but show no great range of variability 
in actual size. 
Description of Decay in Chestnut . — The first evidence of in- 
cipient decay in chestnut wood is the appearance in the wood of 
irregular areas in which the tissues have lost their natural brown 
coloration and become grayish-white (Fig. 5, lo). These areas are 
I mm. or less in cross diameter by 5-25 mm. in longitudinal di- 
rection. The wood between the lighter areas remains as sound 
5 Direct evidence of the causal connection of Hymenochaete rubiginosa 
with the peculiar rot which accompanies it, has not been obtained in the pres- 
ent study. It is reasonable to assume that the rot in question is caused by 
this species since it always accompanies this form on chestnut. Further, the 
same type of rot is associated with this fungus on oak. This evidence, though 
not conclusive, leads to the inference that this peculiar decay of oak and chest- 
nut is caused by H. rubiginosa. 
« In length and taper, fibrous tracheids resemble fibers ; in width and 
bordered pits, tracheids. 
