120 College of Forestry 
radial direction than in any other. In the more advanced 
stages of decay the broad medullary rays are still fairly 
sound and can be separated readily from the other elements 
which are considerably decayed. The numerous broad 
medullary rays which transverse the annual rings of growth 
serve to bind together the layers of growth so that there can 
be no separation along the line of the annual rings. In this 
way the medullary rays act as reinforcing structures so that 
the decayed wood responds far less to radial than to tangen- 
tial compression. They likewise serve to increase materially 
the transverse breaking strength of the decayed wood. In 
consequence of the strengthening effect afforded by the 
medullary rays of this wood a trunk of chestnut (or any 
other) oak rotted by Polyporus pargamenus would resist 
breaking longer than those of most any other kind of wood 
decayed to a like extent by the same species of fungus. 
Microscopic Characters of Decayed Wood.—The dissolu- 
tion and course of the delignification of the woody elements 
is as near like that described for yellow birch wood as could 
be expected of a wood of such dissimilar structure. The 
thick-walled wood prosenchyma elements are the first to dis- 
appear and are closely followed by the thin-walled ones. 
After the disappearance of these elements the decayed wood 
appears skeletonized. At this stage of the decay the uni- 
seriate pith-rays, the tangential. rows of wood parenchyma 
cells, and the partially dissolved small vessels are still visible 
and are the only elements remaining within the intersections 
formed by the radially extending pith-rays and the tangen- 
tial rows of. wood parenchyma cells of the late wood. In 
this connection it may be mentioned that the late wood decays 
faster than the early wood of the annual ring, since the latter 
is composed mostly of large vessels surrounded by tracheids, 
both of these elements being highly lignified in this portion 
of the growth ring. Within the late wood of the growth 
ring the wood parenchyma cells are the next elements to dis- 
appear. By the time the parenchyma cells have disintegrated 
more or less completely the uniseriate pith-rays and the 
small vessels begin to break up. The large vessels in the 
