Feb. ip. i9i7 Arsenical Injury through the Bark of Fruit Trees 
1,5, and 6, while above the ground it had darkened but slightly. A 
corresponding change had taken place in the texture of the bark. All the 
dead bark was very tough and fibrous when first killed, and on all aerial 
portions it remained so, but on the crowns below the surface of the 
ground it gradually became so disintegrated, especially on those with 
the darkest color, that it could easily be picked apart with the fingers. 
When dry, it was rather brittle; when wet, it was so soft as to be almost 
pasty in certain portions. It seems probable that this disintegration 
is largely due to the invasion of saprophytic microorganisms rather 
than to the direct action of the arsenicals. 
Comparing the injury through rough bark with that through the 
smooth bark of the crown, in both cases unwounded, we find that the 
smooth bark is vulnerable through lenticels and the rough bark through 
cracks or fissures caused by growth in the cambium region. Either is 
sufficient to make possible the girdling of the tree or limb at the point 
of application. Which permits the more rapid absorption depends 
upon conditions and is, indeed, of little moment. 
INJURY THROUGH ROOTS 
As most of the spray mixture applied to a tree eventually reaches the 
ground under it, the likelihood of injury to the roots or to the whole tree 
through the roots is a subject of interest. 
INJURY FROM BANDAGES 
A few roots were treated by the bandage method used largely on the 
branches. The number so treated, however, was relatively small for two 
reasons: First, the amount of work required is vastly greater than if 
branches are used, and, second, it is almost impossible to uncover roots 
and apply bandages to them without wounding them. Most apple 
roots of a suitable size are covered with fine rootlets the removal of which 
makes wounds that readily admit the arsenic. However, enough were 
found free from all side roots to make it possible to establish the following 
facts: (1) That the unbroken periderm is quite resistant to the absorp¬ 
tion of arsenical compounds, (2) that some of the lenticels will admit it, 
and (3) that when admitted through a wound the effect is about the same 
as in a branch of the same size. Indeed, we came to regard the suscepti¬ 
bility of roots X inch in diameter or larger as about the same as that 
of branches of equal size. 
INJURY BY ABSORPTION THROUGH THE FINE FEEDING ROOTS 
In addition to the possibility of a localized injury of crowns or roots 
by a heavy accumulation of arsenical insecticides that have run down 
the trunks, we must consider the likelihood of small amounts mingling 
