(2 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE. 
No essential difference was noted in trees grown from root grafts 
made from healthy seedling trees taken from a locality where nursery 
stock had been grown for many years as compared with those taken 
from a new locality where stock had not been grown previously. 
Heavy, stiff, clayey, wet soils apparently increase the amount of 
disease, especially of crown-gall, in nursery stock. Some lighter soils 
show an increase of hairy-root. 
In nursery experiments the amount of crown-gall present after the 
first year decreased considerably from year to year, while hairy-root 
increased slightly, especially during the first two years. In the 
orchard experiments the amount and intensity of the forms of the 
disease decreased instead of increasing, indicating that older apple 
trees In many cases successfully resist both hairy-root and crown-gall 
and that many may recover completely. 
Crown-gall and hairy-root affected nursery trees in the experiments, 
stunting them very slightly and causing them to be only 90 to 94 per 
cent as large as healthy trees. In the experimental orchards the 
apparent effect on the growth of trees was even less—in fact, hardly 
perceptible. These experiments prove that the effect of crown-gall 
and hairy-root upon apple trees in the orchard has been overrated, 
at least in the established apple districts of the Contra) and Eastern 
States. 
A marked difference in the susceptibility of varieties of apple trees 
to crown-gall and hairy-root has beennoted. Trees of some varieties, 
when grown from rootgrafts, tend to develop a large amount of crown- 
gall; others of hairy-root, in both cases chiefly on the scion portion of 
root-grafted trees. In these experiments, the Wealthy, the Yellow 
Transparent, and the Wolf River were the varieties most diseased 
with crown-gall; and the Ben Davis, the Wolf River, and the North- 
ern Spy were most diseased with See sere | 
The period when most apple root grafts become diseased with 
crown-gall is apparently the time when the wounds in the union are 
being healed by the formation of callus. If the disease could be kept 
out during this period it is quite probable that little would occur on 
nursery stock except as it gained entrance later through wounds made 
in cultivation. 
In the experiments, with the fitting of root grafts, where poorly 
fitted, especially if the lower end of the scion projected, an increase 
of both crown-gall and hairy-root occurred. The disease apparently 
did not spread from tree to tree in the nursery rows in the experiments, 
since there was little or no increase of disease after the first year. 
Little of the crown-gall occurring in root-grafted trees can with 
certainty be accredited to the fact that grafting knives as a tule are 
not sterilized. 
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