APPLE DISEASES 
isolated from several kinds of plants have 
proved easily cross-inoculable artificially 
to numerous other species in different 
plant families. More than one orchardist 
has also had practical proof of cross in- 
fection through contaminated soil. Con- 
sequently wise growers will hesitate to 
risk the chance of transmitting crown 
gall from one kind of cultivated crop to 
another by planting susceptible varieties 
in ground from which plants diseased 
with crown gall have recently been rooted 
out. 
In the following paragraphs we give 
some information regarding the character 
and seriousness of crown gall as it ap- 
pears on some of the more important 
cultivated fruits: 
The Apple 
Upon seedlings and root-grafted trees 
in the nursery we find principally the 
hairy root condition. or galls of a some- 
what fleshy nature. (See Fig. 2, A and 
B.) On older trees the persistent peren- 
nial hard galls are more frequent and in 
the orchard there appears also upon the 
461 
trunks and branches an aerial form of 
the disease. Aerial tumors are rarer than 
the root or crown form in most localities. 
They are characterized by the growth 
of smooth, woody, persistent swellings, 
which later become warty from the ap- 
pearance of numerous stubby roots which 
break out. just to the surface. It is not 
possible for us-to state at present exactly 
how these aerial tumors originate, but 
the causal organism is similar to that pro- 
ducing other forms of crown gall. 
Crown gall and hairy root are very 
prevalent in the nurseries, and because 
of laws forbidding the sale of trees affect- 
ed with this contagious disease, the an- 
nual loss to nursery men is very large. 
Unscrupulous dealers sometimes cut off 
the galls and sell the trees, but tumors 
may reappear on such trees. Certain pre- 
cautions may be adopted, however, in the 
care of young trees and in the methods 
of grafting which will reduce greatly the 
amount of disease in the nursery.7 
+See Bulletin 168, Bureau of Plant Industry, 
U. S. Department Agriculture. 
Vig. a A, 
Crown Gall on Young Apple Tree. 
B, Hairy Root on Young Apple Tree. 
