HARVARD UNIVERSITY. 
BULLETIN 
OF THE 
BUSSEY INSTITUTION. 
No. 1. — On the Power of some Peach Trees to Resist the 
Disease called ‘‘ Yellows.” By E. W. Morsr, Instructor 
in Natural History. 
In the light of the knowledge concerning life processes that we 
now possess, the phenomenon known as ‘‘peach yellows” is 
; manifestly a reaction of the peach tree tissues to some external 
influence. Inasmuch as this reaction is not normal to peach trees, 
it must be due to some weakness induced by an unfavorable envi- 
ronment either during the life of the individual plant in question 
or that of its ancestors. Since the trees which suffer from 
‘¢ yellows” usually show no sign of the disease in their youth 
(if it were otherwise they would never have been transplanted to 
a cultivated orchard), the only reasonable supposition is that they 
have been subjected to some unfavorable influence during the 
same generation in which the disease appears, or at the most in 
an earlier generation not very remote. In other words, a peach 
tree in which the malady occurs is, or has been, subjected to 
an environment differing from that of its ancestors, for otherwise 
the latter could not have survived to reproduce their kind. 
Suggestions of external factors which might produce the disease 
have been many, but they may be classified as follows : — 
(a) Microbes. 
(6) Mechanical injuries. 
(c) Improper soil conditions. 
(ad) Punctures of insects. 
(e) Unsuitable climate. 
(f) Enzyms. ; 
