A STUDY OF HEART-ROT IN WESTERN HEMLOCK. 



25 



of the protective, tissues of the host plant was necessary in order to 

 produce infection. A portion of the field data was obtained with the 

 principal object of determining the part played by the degree of injury. 

 All injuries were noted as to size, height on tree, side of tree affected, 

 total number, and condition (whether healed or not healed) ; when- 

 ever possible the age when the injury was inflicted and the time taken 

 to heal were also noted. A special effort was made to determine, if 

 possible, the particular injury causing the original infection. This was 

 generally taken to be at the point on the trunk where the oldest sporo- 

 phore appeared. Table IV gives summaries for the river-bottom 

 and southwestern-slope types, respectively, based upon an age-class 

 division of the trees. 



Table IV. — Relation of injuries causing heart-rot to' the age and to the total stand of 

 western hemlock trees on plats of the river-bottom and southwestern-slope types. 





Infection traced to— 







Av- 

 erage 



de- 

 gree 

 of in- 

 jury. 



1 





Type and age class. 



Branch 



stubs. 



Frost 

 cracks. 



Broken 

 . tops. 



Miscellane- 

 ous injuries. 



Uninfected 

 trees. 



Num- 

 ber of 





Num- 

 ber of 

 trees. 



Per 



cent. 



Num- 

 ber of 

 trees. 



Per 



cent. 



Num- 

 ber of 

 trees. 



Per 

 cent. 



Num- 

 ber of 



trees. 



Per 

 cent. 



Num- 

 ber. 



Per 

 cent. 





River-bottom type: 

 41 to 100 j'ears.. 



103 



7 



110 



91.2 

 100.0 



1 

 



1.0 



3 

 



2.6 



a2 

 



1.7 



4 

 



3.5 



1.19 

 2.05 



113 



101 to 160 years... 



7 







Total 



92.5 



1 



.1 



3 



2.5 



2 



1.6 



4 



3.3 



1.14 



120 







Slope type: 



41 to 100 years 



9 

 12 

 16 

 22 



60.0 

 66.6 

 70.0 

 88.0 



1 

 



1 







6.7 

 "i'.O 





 1 

 3 

 2 



5.' 7' 

 13.0 

 8.0 





 2 

 3 

 1 



'ii.'i' 



13.0 



4.0 



5 

 3 

 

 



33.3 

 16.6 



1.3 

 2.1 

 2.5 

 2.6 



15 



101 to] 60 years 



18 



161 to 200 years 



23 



201 years and older 



25 



Total 



59 



72.8 



2 



2.6 



6 



7.4 



6 



7.4 



8 



9.8 



2.1 



81 







a Windfall scars. 



Table IV shows that by far the greatest percentage of infection was 

 attributed to branch stubs (figs. 6, 7, and 8). 



This amounted to 92.5 per cent in the river-bottom type and 72.8 

 per cent in the slope type for the total stand in each type. Broken 

 tops come second, and miscellaneous injuries, such as windfall and 

 logging scars, etc., reached a percentage of 7.4 in the slope type and 

 1.6 in the river-bottom type. Grouped under miscellaneous causes 

 were such injuries as blazes, logging, windfall and fire scars, lightning, 

 etc., and a considerable amount of sapsucker injury. The first infec- 

 tion was not attributed to a certain injury unless the development of 

 a sporophore on it (fig. 2) showed this to be the most apparent point 

 of infection. The relative degree of injury as determined upon a 

 basis of age class is shown in figures 11 and 12, taken from Table IV 

 under the head of "Average degree of injury." This shows an increase 



