134 College of Forestry 
This, however, depends largely upon the age of the tree, 
structure of the wood, and the durability of the heartwood of 
the attacked species. 
In still later stages of the decomposition two or more 
adjoining decayed areas or pockets frequently coalesce into 
one so that the wood has a decided ** pocketed ” appearance. 
The individual pockets are highly irregular in outline and 
their size depends entirely upon the extent of the decay. 
The largest pockets observed were in yellow birch wood, 
where they attained a maximum size of three mm. in 
diameter and three em. in length. In general the greatest 
dimension of the pockets occurs in the same direction that 
the woody elements extend; occasionally, however, it extends 
at right angles to them. In the later stages of the decay the 
individual pockets are quite empty of contents save for a few 
scattered tubular elements — the vessels. Owing to their 
greater lignitication these elements are the last ones to dis- 
appear under the dissolving action of the fungus in most 
woods. | 
In woods with very broad pith-rays, such as the maples 
and oaks, the larger pith-rays outlast the vessels and are the 
last element to disintegrate under the dissolving action of 
the fungus. In those woods having such broad pith-rays the 
tendency to the formation of pockets is more or less retarded 
by the presence of these pith-rays which are very resistant 
to decay. The broad pith-rays possessed by both maple and 
oak offer exceptional resistance to the spread of the mycelium 
in any other than a radial or horizontal direction. In the 
late stages of the decay these broad pith-rays which trans: 
verse the annual rings of growth in a radial direction, serve 
to bind together the layers of growth so that there is no 
separation of the decayed wood along the line of the annual 
rings as usually oceurs in those woods which lack the broad 
pith-rays. Woods possessing such broad pith-rays would tend 
to resist the decay produced by Polyporus pargamenus much 
longer than other woods which lack them. The former type 
of woods, when decayed while in use, would hold under the 
