3*6 . 
'Journal of Agricultural Research 
Vol. VIII, No. 8 
in no case of trees entirely removed was this region affected except in 
those having the upper portion of the crown extensively killed and the 
dead area extending down underneath. This disproportionate injury 
of crown and branches suggested a systemic poisoning in addition to the 
effect brought about by girdling. 
A considerable search was made for evidence of parasites. Repeated 
examinations were made with a good traveling microscope, and material 
for cultures was taken back to the laboratory at Bozeman. A very 
small proportion of the crowns was found to be attacked by the blight 
organism Bacillus amylovorus , but these were easily distinguished from 
the others by field observation. A few cases differed from the blight 
and from the crown injury more commonly found in that the dead bark 
was tougher, juicier, and a more red-brown in color with a distinctly 
stratified appearance. By microscopic examination no microorganisms 
were found in these cases, and cultures from the inner bark yielded noth¬ 
ing. Our efforts to find parasitic fungi or bacteria in the more common 
form of the trouble, either by microscopical examination or by culture, 
yielded no positive results, though some saprophytes were found, as 
might be expected. We would, however, warn the reader against con¬ 
cluding from this evidence that the possibility of a parasitic agent was 
eliminated, for all experienced plant pathologists are aware that much 
more extended work would be required to justify such a contention. 
Our observations on this trip brought no evidence against the arseni¬ 
cal theory. On the other hand, the contention of Ball and others (i, 2) 
that this trouble is caused by alkali and seepage water appeared wholly 
untenable, as many of the trees were in positions where such conditions 
were absent and there seemed to be no especial prevalence of crown 
injury where they occurred. 
It is apparent from Ball's publications that he was confusing two 
troubles sharply separated by Headden,who alleged them to be due, 
respectively, to arsenical poisoning and to an excess of nitrates in the soil 
(6, 8, 9). That the latter may be due to alkali and seepage is debata¬ 
ble, but that is not within the scope of this paper. 
We have established conclusively that arsenical compounds used as 
insecticides can be made to injure the crowns of trees under conditions 
very similar to those that result from some orchard practices. Whether 
or not such compounds are responsible for killing the trees under dis¬ 
cussion in Colorado or elsewhere, or any portion of them, is quite a dif¬ 
ferent question, and each reader will form his own opinions from the 
evidence. 
We wish here to emphasize the importance of making further studies 
to eliminate or establish other factors as causative agents for this trouble, 
especially parasitic organisms and climatic conditions. The former 
possibility has been hardly touched so far as Colorado is concerned, 
though many brief studies of forms of “collar-rot” and “crownrot” 
