i 
70 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE. 
lings in a nursery row without further treatment. Of those living at 
the end of one year, 14, or 36.8 per cent, recovered; 16, or 42.1 per 
cent, developed traces of crown-gall; 3, or 7.9 per cent, developed 
large galls; and 5, or 13.2 per cent, developed hairy-root. At the 
same time there were planted in an adjacent row a number of the 
same lot of seedlings with both hard and soft galls remaining attached. 
During one season’s growth 12, or 37.5 per cent, made no further 
development; 15, or 46.9 per cent, Increased in size in pace with the 
growth of the tree; and 5, or 15.6 per cent, developed hairy-root 
from their surface. All that hved made a good growth. Of the first 
lot 25 per cent died, presumably nearly all from wounds, and of the 
second lot only 3 per cent died. 
In planting an orchard it is better to plant healthy trees and take 
no risk of diseased trees recovering, since only about one-third of 
the trees diseased with crown-gall, as shown by experiments, fully 
recover. The initial cost of the orchard is only a small portion of 
the total cost of mamtenance, and in general it pays to plant the 
best rather than to plant and attempt to cure diseased trees. 
SUMMARY. 
The disease or diseases of apple trees manifested by the forms or 
types known as crown-gall and hairy-root occur in nurseries and 
orchards in the United States wherever apple trees are grown. They 
have been reported in one or more forms from Europe, South Africa, 
New Zealand, and Australia. 
The crown-gall type of the disease occurs on apple trees in two 
forms; the soft and the hard. The former differs slightly from the 
latter, especially in its more rapid growth, softer texture, and less 
permanent nature. Apple crown-gall in both forms is related to the 
crown-gall of the almond, apricot, blackberry, cherry, chestnut, 
grape, peach, pear, plum, prune, raspberry, rose, and walnut. 
The hairy-root type of the disease is of four forms: The simple 
form, characterized by numerous roots springing at right angles 
from a larger or main root; the woolly-knot form, characterized by 
numerous more or less parallel roots springing from a hard gall or 
swelling on a longer root; broom-root, a side root which is much 
fasciated with fine branch roots, often negatively geotropic; and aerial 
tumors, or knots, which are the woolly-knot form on the limbs of the 
trees. All of these forms of hairy-root are probably directly related 
to the forms of crown-gall, but for convenience and clearness they 
are discussed and treated separately. 
The soft form of crown-gall is most common on yearling apple 
seedlings, though usually not abundant. It is occasionally found on 
budded and root-grafted trees. The hard form is common on budded 
186 
