24. BULLETIN 722, U. S. DEPARTMENT OF AGRICULTURE. 
relations to the degree of infection and included within the first 
eight factors of the graph, there is apparently no one which stands 
out. The factors of height, diameter, crown size, total volume, and 
lack of vigor show increase with increased age, so that no special 
importance can be attached to these in so far as any one directly 
influences the rate of decay. The data herein given are not sufficient 
proof that vigor is the one outstanding factor influencing decay; 
since vigor is expected to decrease with increased age, the parallelism 
of increased decay and decreased vigor can not be interpreted as a 
direct influence exerted by vigor. No doubt vigor plays an im- 
portant part in the speeding up or slowing down of the rate of decay 
in a tree, if only this relation could be determined accurately and 
definitely. 
The total rot percentage for the entire stand of the bottom type 
is 26.6, as compared with 30.8 per cent for the slope type. This 
slight difference in the percentage of total rot for the two types (where 
a greater difference might be expected) is significant and is no doubt 
due to the fact that under each site are grouped all the trees, ranging 
from the youngest to the oldest. A comparison of the percentages of 
infected and uninfected trees for the two sites shows a striking differ- 
ence in results from different methods of presenting the amount of 
infection in a stand. In the river-bottom type, 97 per cent of the 
trees were infected and 27 per cent of the wood decayed. In the 
slope type, 90 per cent of the trees were infected and 31 per cent of 
the wood decayed. A comparison of these figures indicates that ease 
of infection is the factor in which the bottom type exceeds the slope 
type and the rate of spread of decay in the trunk is less speeded by 
bottom location, if at all. The latter belief seems to be borne out by 
the fact that the rate of spread in the bottom type must neeessarily 
have been slow, since the stand was composed of comparatively young 
trees of small heartwood content. 
In the slope type the environment is favorable to the full develop- 
ment of tree growth, with an environment equally unfavorable to the 
development of fungi. The reverse is true of the river-bottom type. 
This is evidenced by the facts brought out in Table II (figs. 11 and 12), 
which show that decay is more pronounced in the river-bottom type 
than in the other. The graphs also show that in the 41 to 100 year 
age class (Table III) the conditions for the best development of the 
health of the trees were far below those for the 101 to 160 year age 
class. 
RELATION OF DECAY TO INJURY AND TO SPOROPHORES. 
The relation of injuries to decay in respect to furnishing entrance 
points for infection has been accepted with little opposition, and in 
many instances in culturing fungi it has been found that the opening 
