572 BULLETIN 347 
“As to the nature of the wound necessary for infection, they conclude 
that any kind of wound in the bark deeper that the outer green cortex — 
may furnish an entrance. £ 
The fact that a large proportion of incipient cankers occur about dead 
twigs, or small branches, has suggested that the pathogen gains entrance 
to the living tissue through the dead tissue of such branches. But it is 
usually impossible to tell whether the dying of the twig preceded the 
entrance of the fungus, or whether the twig died as a result of the canker 
having been formed about it. Other reasons could be assigned as explain- 
ing the above condition. The rough bark around the insertion of small . 
branches remains moist longer than does smooth bark, and thus furnishes 
more favorable conditions for spore germination. Insect injuries are 
more numerous at such places and also the bark often becomes cracked 
above the insertion, thus offering more opportunities of entrance to the 
parasite. 
Age of tree and parts of host affected.— After the first year the age and 
the size of the tree make no difference in its susceptibility. Not only 
may cankers be found in the woods just as often on trees an inch in 
diameter as on those two feet in diameter, but also inoculations on large 
trees produce the disease just as surely as do those on small trees. Also, 
there is no difference in susceptibility between the trunks and the branches 
of any size. Inoculations produce the disease equally well on all. 
All inoculations of green leaves have failed. Murrill.(1906 a) was unable 
to produce the disease on green shoots of the first year. Metcalf and 
Collins also state that green twigs are not affected. Metcalf (1913:365) 
states: ‘Late in the season it will readily attack wood of the current 
year.” Anderson and Babcock (1913), however, successfully inoculated 
first-year green shoots both with ascospores and by inserting diseased 
bark; Rankin (1914) also produced the disease on first-year shoots 
by inoculation with ascospores at Napanoch, New York. Yet it is readily 
apparent that green shoots are less often attacked than are older ones; 
also the percentage of infection is higher during the latter part of the 
growing season than during the early summer. ll inoculations made 
by the writers on green burs have failed. 
Metcalf and Collins (1910) state that roots are rarely, if ever, attacked, 
but the pustules of the fungus are commonly. found on exposed roots; 
Anderson and Babcock (1913) were able to grow the fungus on subter- 
ranean roots, also, but no typical cankers were produced. It is certain 
that the roots are not killed by the fungus, because they seem not to lose 
their power of producing new shoots even when the part of the tree above 
ground is entirely killed by the parasite. 
The orientation of lesions on the trees shows no relation to the points 
of the compass. Data compiled for nearly a thousand trees taken at 
