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. 47^8) 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 

































































































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O 20 40 60 80 IOO 20 40 60 80. 200 ZO AO GO 80 300 SO 40 60 SO 400 



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, commonry 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 woimded 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 



