A STUDY OF HEART-ROT: IN WESTERN HEMLOCK. 20) 
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 originalinfection. 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— 
\ Uninfected | Av- 
Branch Frost Broken | Miscellane- trees. erage | m- 
Type and age class. stubs. cracks. tops. ous injuries, gee BEnOE 
ge otek RISENER ce trees 
of in 
Num- Num- Num- Num- jury. 
ber of at ber of et ber of et ber of B oe pe eee : 
trees. *| trees. * | trees. | * | trees. VELelleats . 
River-bottom type: 
41 to 100 years.-...._..- 103 | 91.2 1 ale) Salen 256 OX Ns 7 4} 3.5 | 1.19 113 
101 to 160 years..._.__:. 7 ;100.0 On east OR |S Aaee On eeens= OF ES see 2.05 7 
Lotaleetye sashes a 110 | 92.5 1 at Salen 2a laeleG 4] 3.3]1.14] 120 
Slope type: SA 
41 to 100 years.......... 9 | 60.0 IL f8R 7 QHESSASc ah feet 8 ae 5 | 33.3 | 1.3 15 
101 to 160 years......_.. 12 | 66.6 Os|asees 1 5.7 2} 11.1 3 | 1656) 221 18 
161 to 200 years....._... 16 | 70.0 1} 4.0 3 | 13.0 3 | 13.0 On| Fee 2.5 23 
201 years and older..___. 22 | 88.0 CO) eal eee PAN? 0) Ii} ZE@ Od ee seers 2.6 25 
MO bale eee 59 | 72.8 Zia 256 Gullearierd: 6| 7.4 8 | 9.8] 2.1 81 
a Windfall sears. 
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 
