6 
Colorado Experiment Station 
ditions, the bark of the crown has' been completely disintegrated and 
almost always that of the roots next to the crown. Its structure has 
been wholly destroyed and the woody tissue beneath has been stained 
brown. In bad cases its structure too has been destroyed so that under 
the' rasp it often acts as though thoroughly charred, outwardly it is 
often blackened. The bark of such trees is usually a reddish yellow 
frequently showing longitudinal cracks. The woody tissue of the lower 
portion of the trunk is stained brown though the tree may still be alive. 
This is shown in Plate 3, Fig. 3, p. 14, Bulletin 131, which is a portion 
of the lower part of the trunk of a Ben Davis tree dug up when in full 
bloom. The bark on this portion of the tree was intact and the staining 
was not due to dead wood exposed to the air. 
The*Yellowish-Red, Bark Not Diagnostic. 
The yellowish-red color of the bark of the limbs and twigs of such 
trees is probably the result of malnutrition rather than of the direct 
action of the arsenic and while this color is very commonly present in 
cases of this trouble, I cannot consider it as a diagnostic feature. 
The Point of Attack in Cases of Irritant Poisoning. 
The attack on the bark is evidently made from the outside because 
we find patches on some of these trees where the girdling is not yet 
complete and while the outer portions of the bark may be disintegrat¬ 
ed the inner portion may be apparently entirely healthy. There are no 
signs in such cases that the bark has ever been raised or loosened from 
the underlying tissues. These facts necessitated the examination of trees 
in which the trouble had not advanced to this stage. Samples were 
easily found showing all stages of the progress from the inciptent at¬ 
tack in which the disintegrated hark formed only a very thin layer on 
the outside to tnose in which it had finally perforated the bark and 
attacked the underlying wood. In some orchards we find some degree 
of this girdling- on almost every tree. I have in mind at this writing 
a pear orchard, containing possiblv 300 trees, in which I failed to find 
a single tree which did not show this corrosive action of arsenic in a 
marked degree and in many cases the bark had already been per¬ 
forated. 
The Roots. 
The above remarks apply to the roots especially at their juncture 
with the trunk; sometimes we find the whole of this portion of the 
root involved, again only the upper portion, if the attack has not ap¬ 
proached very near to the final stages. On the roots we often find a 
very sharply defined limit to the trouble just as we u ually do as we 
approach the surface of the ground. The distal portion of the roots 
are as a rule in better or even good condition. This point was well il¬ 
lustrated by the case of a pear tree root which I dug out. The root 
was entirely dead near the trunk, but was apparently healthy a few 
feet away and had thrown up sprouts. 
