14 
Colorado Experiment Station 
the roots joining onto the base of the trunk is almost invariably 
involved. The attack may, in a few instances, begin on the -roots 
but the number of these instances is small. 
The Effect of A rsenic on Trees. 
I have a record of about twenty trees, the greater portion of 
which I have seen myself, that have been injured or killed by arsenic, 
either in the form of arsenious acid, sodic arsenite, calcic arsenite or 
lead arsenate. 
In Bulletin 131, page 19, I referred to experiments of others 
made to establi h the effect of arsenic upon vegetation and gave the 
results of a few experiments made with greenhouse plants and cited 
the cases of two trees which I had met with, one of them presenting 
with great clearness the action of arsenic, particularly in the form of 
arsenious acid, upon the bark and woody tissues of the tree. I 
then stated that I gave the case in considerable detail because I be¬ 
lieved it to present as conclusive an illustration of the action of 
arsenic upon trees as could possibly be adduced. I have since then 
seen several trees injured by the same cause, sodic arsenite, and 
while they each present an essential reproduction of that case, none 
of them have been any more marked or presented any feature more 
forcibly than it. I shall therefore use it again to show that soluble 
arsenical compounds when present in sufficient quantities will 
kill trees, secondly to show in some detail what the action of arsenic 
is on the tissues of the tree, particularly upon the bark and the woody tis¬ 
sues. The condition of this tree in the following April is shown 
in Plate I, taken from Bulletin 131. 
The arsenic used in this accidental experiment was sodic arsenite 
emptied into an irrigation ditch, twelve feet distant from the tree. This 
was done in the month of June when the tree was in active growth. 
Two days later a portion of the tree was sick or dead, the person 
describing it said dead. I was not present that day. The limb 
never showed anv signs of life afterward, the killing was thorough. 
Mr Whipple and I subsequently dug out the poisoned root of this 
tree tracing it from the trunk to the point in the irrigating ditch 
where the arsenic had been emptied into it. The other roots of this tree 
which we encountered were aoparently normal. Even those branches 
of this root which ran parallel to the ditch and whose feeding area 
had not received any of the arsenic also appeared normal. The root¬ 
lets within whose feeding area the arsenic had come were dead, being 
black and brittle. We could see the course of the arsenical solution 
from the rootlets to the tip of the twigs as the root lay in the trench 
which we had dug to expose it. The lateral branches of the root 
and the two side sections were normal in appearance, the top section 
and also the bottom section had been very strongly attacked. The 
bark of the root on the two sections attacked was thoroughly dis¬ 
integrated and two irregular sections of the woody tissue of the root 
were killed and stained brown, shown in Plate II, Fig. I. The total 
