48 
BULLETIN" 871, U. S. DEPARTMENT OF AGRICULTURE. 
order to emphasize the fact that while the increase in the number of 
wounds is closely followed by an increase in infections, the increase 
in the amount of cull due to decay is not a direct function of the 
increase in infections, but is also dependent upon the factor of age 
and thrift, as previously explained. 
Meinecke (16, pp. 47-48) found in white fir that a combination of 
suppression and severe wounding was a prerequisite for serious 
decay in trees up to the age of 150 years. This does not hold for 
incense cedar. Of the ten severe cull cases in suppressed trees up 
to the age of 165 years, five occurred in trees slightly wounded, one 
in an entirely unwounded individual, and only four on severely 
wounded trees. Of the four dominant trees below the same age 
with severe cull cases, two are severely wounded and two slightly 
90 
80 
70 
60 
l 40 
30 
20 
JO 
ofs 
1>V 
i 
V 
20 40 60 
40 CO SO 300 20 40 60 60 ACQ 
\0O 20 40 60 80. 200 20 
Age - Vears 
Fig. 3.— Relation of the age of incense-cedar trees to wounds, infections, and cull. 
wounded. And, in fact, throughout all the age classes occur trees 
slightly wounded but with severe cull cases. 
The foregoing considerations lead to the following conclusions: 
(1) Fire is responsible for by far the greatest number of dry-rot 
infections, commonly leading to serious decay, resulting in heavy 
cull. Fire is three times as important as its closest competitor, 
knots. (2) Knots are responsible for some far-reaching decay, but 
most of the infections through knots are confined to the immediate 
vicinity of the knot. (3) Aside from fire and knots all other means 
of entrance for decay are of little import. Lightning would be 
serious except that wounding from this source is rare. Frost is of 
no importance in promoting inoculation, since the wounded surface 
presented is small and frost cracks are relatively few. However, 
frost cracks often assist in carrying the dry-rot over a greater length 
of the bole than would be normal. Damage from unknown causes 
leads to some infection, but it is not of much importance. Infections 
