306 Journal of Agricultural Research voi. viii, no. s 
From these repeated experiments, therefore, it seems safe to conclude 
that when arsenicals are applied by this method to either wounded 
or unwounded limbs they injure the different varieties of apple about 
equally. Certainly neither the Ben Davis nor the Gano is especially 
susceptible under these conditions. However, as the governing factor 
seems to be the outer protective covering, and as this covering is very 
different on the smooth-barked limbs and on the rough-barked crowns 
extensive tests on the latter might yield different results. No Ben Davis 
or Gano trees were available for crown treatment, however, and many 
might be required to make conclusions free from experimental error. 
Without these two varieties such a test would miss the point of greatest 
interest. 
EFFECTS OF SEASON UPON INJURY 
As this investigation was carried on during several months of spring, 
summer, and fall, it is of some importance to know whether the season or 
stage of growth influences the extent or character of injury. To deter¬ 
mine this, a considerable number of tests was made during every month 
from March to October, inclusive. From the specific treatments made 
for this purpose and others that have contributed to our information on 
the relation of season to injury, we conclude that when the trees are 
frozen the injury is very restricted, being confined wholly to the exposed 
tissues of the wounds. When the trees are more or less active, even 
before the leaves come out in the spring and after they drop in the fall, 
the injury will readily extend a considerable distance from the point of 
treatment. Throughout this active period the extent of injury from a 
given treatment is about the same, but it runs its course a little more 
rapidly just after the leaves come out and more slowly about the time 
they are dropping in the fall. 
INJURY THROUGH THE ROUGH BARK OF LIMBS, TRUNKS, AND 
. CROWNS 
Casual observation might lead one to believe that the heavy, rough 
bark on the trunks of trees is a better protection against all kinds of harm¬ 
ful agencies than the thin, smooth bark of the small branches. That 
it does offer a greater protection against mechanical injuries is undis¬ 
puted, and it is also true that the thicker, projecting portions of the rough 
bark are highly protective against the absorption of arsenical compounds 
when added to the unwounded surface. Between these thick ridges 
however, are the furrows in which the corky layer is more or less broken. 
As the tree expands in diameter new rifts are formed or the old ones 
are reopened. Microscopic study confirms what close macroscopic obser¬ 
vation suggests, namely, that the rough bark has vulnerable points of a 
character not found in the periderm of the branches above. 
It has often been observed that when a tree is thoroughly drenched 
with a spray mixture a considerable quantity of this runs down the trunk 
