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 mcrease 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 mterpreted 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. Tliis 

 sHght 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, rangmg 

 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 

 mfection 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 necessarily 

 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 tj])e. 

 This is evidenced by the facts brought out in Table III (figs. 1 1 and 12), 

 which show that decay is more pronounced m 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 



