34 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE. 
EXPERIMENTS ON THE EFFECT OF THE DISEASE ON APPLE TREES. 
EFFECT ON SEEDLINGS NOT UNIFORM. | 
No extended experiments have been made to determine the effect 
of crown-gall and hairy-root on seedlings. From small experiments 
and from observation the following conclusions have been reached: 
On yearling seedlings with relatively large galls encircling the root 
(Pl. II, fig. 2) or with a very abundant formation of fine side roots 
(Pl. IIT, fig. 1), such as accompany extreme forms of hairy-root, there 
is a perceptible stunting of the growth of the tree. Where the galls 
are small and the hairy-root formation is not extensive, no apparent 
effect on the growth is noted. In the latter case, as the trees grow 
older, they may outgrow the effects of the disease. 
The aerial form of hairy-root (stem tumors) was found in the 
autumn of 1908 on 40 trees in a block of 500 8-year-old seedling apple 
trees in a pedigree orchard near Mitchell, Ind., belonging to the Indiana 
Agricultural Experiment Station. These were first reported in a 
letter by Prof. C. G. Woodbury, of that station. Six of these trees 
bore from 8 to 25 large, rough knots (Pl. V, fig. 1), in some cases 
encircling the tree. None of these trees was quite as large as the 
neighboring trees. No difference in size was noted in the other 34 
diseased trees. 
One striking effect of hairy-root of the simple form should again 
be noted. Seedlings diseased with this form are enabled to root 
more readily than healthy seedlings. Cuttings taken from such 
seedlings root more readily than those from healthy seedlings (see 
p. 24). Such cuttings usually develop into trees (Pl. VII, fig. 1), 
affording to some extent a method of propagation not ordinarily 
used and not to be recommended. 
SLIGHT EFFECT ON GRAFTED TREES IN THE NURSERY. 
The same observations made on the effect of crown-gall and hairy- 
root on seedling trees apply to young grafted trees, except that the 
stunting, as a rule, is not nearly so marked. A great variation in 
effect is shown, since some diseased trees exhibit as great or even a 
greater vigor of growth than healthy ones. On the average, how- 
ever, trees in the nursery rows that are diseased with the simple 
form of hairy-root are not quite so tall as smooth-rooted trees, and 
those with the woolly-knot form may be taller. Those affected with 
forms of crown-gall are somewhat shorter than those with hairy-root. 
In order to determine the effect of the disease on the height of 
trees in the nursery rows, measurements were taken of 18,042 1 and 
2 year old root-grafted trees grown in a number of the experiments 
mentioned earlier in this bulletin. These trees were grown in coop- 
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