124 College of Forestry 
yellow color acquired by the late wood tracheids diminished 
in intensity in the tracheids of the early wood. 
From the above tests “described in full detail, and from 
still other tests employed for the differentiation of both cel- 
lulose and lignin, it is evident that of the individual cells 
the middle lamella is more strongly lgnified than any other 
layer of the cell-wall. The tests employed indicate that the 
tracheids of the late wood are lignified to a much greater 
degree than the other elements of the growth ring. The 
medullary ray cells in the late wood apparently are no more 
strongly lignified than those in the early wood of the growth 
ring. rom the dissimilar structure and microchemical 
reactions of the various elements we would expect the 
tracheids of the late wood to be far more resistant to decay 
than those of the early wood. The cells of the medullary 
rays of the wood examined responded strongly to the iodine 
test for starch, since the wood was cut late in the autumn. 
Macroscopic Appearance of Decayed Wood.— As in the 
other woods studied the first evidence of decay is the oceur- 
rence in the wood of small irregular areas in which the 
tissues have lost their natural light brownish coloration and 
appear as though bleached. As the decay progresses it 1s © 
evident that it is confined to numerous centers of activity, 
resulting in the formation of small pockets separated by 
narrow zones of wood which decay far less rapidly. At first 
the future pockets appear as bleached areas separated by a 
network of wood retaining its natural color. Within the 
individual pockets the decay progresses in a direction parallel 
to the woody elements, and in time the wood in these areas 
rapidly disintegrates and becomes pith-like. ven when the 
decay in the individual pockets is more or less complete the 
wood between the pockets is but little decayed so that it 
appears as a network of lines bounding the pockets. 
The fungus usually begins to decay at the point of union 
of two growth rings. In hemlock wood the progress of the 
decay seems to be dependent upon the physical qualities of 
the woody tissue in the different portions of the growth ring. 
