Feb. i 9t 1917 Arsenical Injury through the Bark of Fruit Trees 
293 
from a comparison of any two treatments. It is possible that a 
thorough anatomical and histological study of branches that showed 
wide differences under identical treatment might have revealed the 
explanation, but the importance of the question did not seem to 
warrant the expenditure of time. 
One of the most striking facts connected with this type of injury 
is the self-limitation of the streaks. At the end of two weeks they 
have practically always run their course, unless the treatment was 
given in late fall or winter. For a week or two longer the margins 
continue to grow sharper and the dead bark becomes more sunken, 
but almost never is there any material lengthening or broadening. 
The explanation of this early limitation is not clear to us. At first 
it seemed possible that the chemicals used contained some soluble 
impurity which became entirely absorbed during the first week, after 
which there was little injury; but this idea has been wholly aban¬ 
doned. We have used chemicals made up with especial care as to 
purity, and we have washed them in many changes of distilled water, 
but the results in this respect were the same (see p. 302). Also, we 
get this same limited course from bandages kept saturated with the 
soluble arsenicals, such as sodium arsenite and arsenic acid. We 
have established quite conclusively that this discolored wood and 
bark conducts the solutions very poorly; this probably has much 
to do with the phenomenon. However, it must be remembered that 
liquids pass rapidly up the xylem ducts and some would be expected 
to reach the leaves at the tip of the branch very quickly before any 
visible change takes place. That some arsenic does actually reach 
distant parts that continue to appear healthy has been established 
by chemical tests made by the Station chemist. It seems quite 
probable that by the action of the tissues through which the chem¬ 
icals pass some of the arsenic is withdrawn from solution, enough so 
that what passes on is too weak to cause the complete death of the 
cells or a noticeable discoloration of the ducts. 
To determine further the relation of the absorption of solutions 
through wounds to the killing of tissues by the solutions absorbed, 
the following experiment was conducted: Three wounded limbs 
were each treated with 10 gm. of calcium arsenite, three others with 
10 gm. of calcium arsenite and 1 gm. of methylene blue, and three 
others with 1 gm. of methylene blue alone. No injury was produced 
by the stain alone, and the injury by the arsenical alone was about 
like that with the arsenical plus the stain. When examined a month 
after treatment, it was found that where the stain was used alone it 
made relatively narrow streaks up and down from the wound. These 
streaks were not visible externally and affected only the youngest of 
the inner bark and extended into the wood for a depth of one to three 
annual rings. They were of an intense blue color near the wound 
