20 BULLETIN 722, U.S. DEPARTMENT OF AGRICULTURE. 
as in semiswamp, bottom sites, decay is prevalent and a retardation 
of growth also results. No relation between the composition of the 
soil and the prevalence of the fungus has been observed. Hemlock 
growing on lime, sand, or clay soils as a base for the regular humus 
layer exhibits no greater proclivity to fungus attack than do other 
species. Of the total answers received, 41 stated definitely that the 
least defective hemlock was found at the upper elevations and slopes 
and upon well-drained soils. The most defective stands were en- 
PER? 1O TRLEF 
CROWN §12E 5QFK 
DEGREE OF INILRY 
NO OF GPOROPA ORES 
EIGHT - FEET 
CROWN RATING 
D.OFL -/NCAES 
*X DEGHEL OF INFECTION 
fay LACK OF IGOR 
Seok 
N a TOTAL VOL CUFF 
N YOL. OF = CUFT, 
5 
8 
% 
8 
t 
s 
ae meee 
NX 
3 
oe 
8 
60 
‘ 
ZO 
N 
@ 
NINES 
N 
GQ 
Q 
4 
4 
A 
4 
4 
& 
~ 
S 
ok 
a 
vA 
: 8 
4 
4 N 
- 
8 
G 
8 
Ee 
a a 
/ 
U 
U 
SX 
Lee 
: <e 
Se 
aa 
ae 
: 
| 
8 
9 
N Ny 
O009 
Fic. 11.—Diagram showing the relation of various factors to the age classes of western hemlock on plats 
of the river-bottom type. j 
countered at lower elevations, on flats and bottom sites, and upon 
poorly drained soils. | 
As the tree grows older it reaches a certain period in its life at which 
its vigor seems to have rached its maximum, after which time the 
vitality of the tree ebbs. This is often spoken of merely as old age and 
is the resultant lowering of vigor due to the increased unfavorable 
environment of its surroundings. Many factors enter into this rela- 
tionship, competition with younger and sturdier trees for light, water, 
and food being the principal ones. - Not the least of these factors is 
the effect of cumulative injuries received throughout its life. Many 
writers on forest pathology have expressed this opinion, and the data. 
following (Table IV) convey a like conclusion. Von Schrenk! states 
that ‘‘it has been pointed out that as trees grow older they become 
1 Schrenk, Hermann von. Some diseases of New England conifers: A preliminary report. U.S. Dept. 
Agr., Div. Veg. Phys. and Path. Bul. 25, p. 51. 1900. 
—— ee ee 
