18 BULLETIN 722, U. S. DEPARTMENT OF AGRICULTURE. 
that the average infection age for the slope type is higher than that 
for the river-bottom type. This is undoubtedly due to the fact that 
the environmental factors in the river-bottom type are more favor- 
able to early attack by the fungus. Crowded stands, much shade 
and suppression, and a higher percentage of atmospheric and soil 
moisture all presumably contribute to the earlier infection in the 
stands situated along the river bottoms. 
It is to be understood that the figures as given in the tables that 
follow are not to be taken as absolute. The small numerical basis 
for some of the data, especially in Table I and part of Tables IT and 
III, and other sources of unavoidable error, make it plain that the 
figures given are to be interpreted as indicative of the true conditions 
and not as an absolute analysis. The general tendencies must first 
be ascertained and the methods for determining them developed 
before absolute figures are presented. 
Tasie I].—Average annual increase in the volume of heart-rot in infected wesiern hem- 
lock trees of the several age classes, on plats of the river-bottom and southwestern-slope 
types. 
Average volume of 
rot (cubic feet). 
Interval Nupiek 
Age class. soe eee Annual | fected 
| classes. |As meas-| 12Crease | __trees 
i aanede between | (basis). 
age 
classes. 
River-bottom type: - Years. Years. 
AGiTOLOONV CATS oss: ose ake ae Jao seen OZ mince eee ae | 0. 27 0 6 
DiMUONOZNV CATS Bye = sees seiner) ae eee eer 60 8 55 035 7 
OSiLONAONVCARS is 7 aes Sores eee eer Ree ee 66 6 . 82 - 045 32 
TAO SO Wee ahes be sose -esacoedoreoouocbocescouce 75 9 | 2.23 -16 39 
Sito 90 Wears2os= ste tecc sea tS son ee eee ae 86 ES) 3. 62 13 19 
Oto dO 2 CaTS 2 a-ha eee eee 95 9 4.04 -05 7 
OA CO REZ GayiCaliS year = ee eer eee 114 | 19 4.21 01 6 
Alliage Classes 4 sé 55 25 Ja ene ee eee ee eae ee ee | 2225 .07 116 
Slope type: 
DAs TONMOKVOAES Mee cos eee oe ye eee mame eS GOs leaeees ates ete ee os 
TAO WO VY CONS Seo esate ns 2 smae See He Bee ee 74 | 10 31 | 02 2 
GONGO 99S V Cars aloe OEE NG So Sei oe ae aetee ie eee 4 | 20} 5 ei 42 - .06 6 
LOM Gow 2OnyiCars 22 24eee ence ee eee eee 110 | 17 14,31 | .8l 6 
ABAETTO WGOkKy ears 5. -e ees Aee ae See eee ee 149 38 16.89 07 9 
NG2ZiCOULO Veanse aide ese sence Saat eee eee 172 23 19.16 -10 ibs 
1LS4°t0: 200) VeatS sa -5 4s Ba ee eo eee eee 193 21 46. 62 1.31 12 
AVEO PPA Nice} aan ke one SSCUSe Een AONE SOEs oes 216 23 46. 56 a .62 13 
226; tO: 306; Wears s fossa. Saeeeie eens le a Pease ee 254 38 73.43 S7All 12 
Alllkace ClASSeS: Sh ai aokee se es cee ce eee Paar Weaacatoces 24.30 46 73 
a Interpolated. 
RELATION OF DECAY TO SITE AND TO AGE. 
Western hemlock, which ranges in decay from 50 to 100 per cent 
of trees infected in some localities and quite generally so over large 
areas where the species occurs in nearly pure stands, may be entirely 
free from its principal disease (heart-rot, caused by Hchinodontwum 
tinctorwum) in some regions. 
hy Cat een 
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