BULLETIN 490, U. S. DEPARTMENT OF AGEICULTURE. 



site on which the trees were located. The amount of butt-rot (prob- 

 ably caused by Polyporus schweinitzii) present on the areas ex- 

 amined was so small that it was not included in the table. This ex- 

 plains any apparent discrepancy between the sum of the sound and 

 defective trees and the total number of trees listed in the table. 



TABLE I. Data on sound and defective felled trees of black jack and yellow pine. 



DISCUSSION OF THE DATA PRESENTED IN TABLE I. 



A study of Table I shows several interesting facts : ( 1 ) There is a 

 marked difference in the percentage of black jack and of yellow pine 

 affected by western red-rot. (2) The site seems to have a decided 

 influence on the occurrence of this rot, especially in the yellow pine. 

 (3) The variation in the percentage of western red-rot on the dif- 

 ferent areas shown in the table is due to several factors, the three most 

 prominent ones being the relative proportion of black jack and yellow 

 pine which had been cut on each area, the influence of the site on the 

 growth of the trees, and the age of the timber. For instance, on area 

 No. 3 the percentage of this rot in yellow pine is high, due apparently 

 to unfavorable growth conditions and the age of the timber cut. 



Table I should give a fairly accurate idea of the occurrence of west- 

 ern red-rot in black jack of merchantable size in this region, since 

 1,855 trees of this kind were examined over areas where 30 to 50 per 

 cent of the black jack 11 inches, d. b. h., and over had been cut. 

 As an indication of the amount of this rot present in the yellow T pine, 

 Table I is not so conclusive, since, with the exception of areas 3 and 

 4, all of the yellow pine shown in the table was of small diameter (12 

 to 18 inches, d. b. h.) and was cut for hewn ties only. This means 

 that the percentage of trees showing western red-rot in the yellow 

 pine on these areas will be greater than is shown in the table, except 



