DEVELOPMENT OF FORMS OF THE DISEASE. Pit 
of healthy trees of the same varieties grown by root grafting. Of 
27 budded trees planted, 5 became diseased, all with traces of the 
woolly-knot form of hairy-root. Of 31 grafted trees, 3 became dis- 
eased with traces of woolly-knot and 1 with the hard form of crown- 
all. 
In the results of these and other experiments in orchards 3 and 4, 
the following facts are prominent: That of the healthy trees trans- 
planted, about the same proportion became diseased as is usual 
in the nursery, but only with traces of the disease, consisting mainly 
of hard crown-gall and woolly-knot; that nearly a third of the trees 
diseased with the hard form of crown-gall recovered; that the soft 
form of crown-gall may develop into the hard form; and that the 
hard form of crown-gall in many instances developed into the woolly- 
knot form of hairy-root. 
A STUDY OF NURSERY METHODS IN ROOT GRAFTING AS RELATED TO 
THE DEVELOPMENT OF THE DISEASE. 
The slight effect of varying the depth of planting the union in root 
grafts.—The effect of deep planting upon gall and hairy-root forma- 
tion has been a matter of much discussion among nurserymen and 
others. Howard (24) concludes from experiments “that the gall 
develops least where the root is long, thus causing the point of union 
between the scion and stock to be near the surface of the ground. 
Especially is this true of clay soil.” 
A number of wholsesale nurserymen growing apple trees on a large 
scale assert that little benefit is gained by using short scions and long 
roots, and that a happy medium of length between the two is best. 
If a long scion is used, placing the union too deep in the soil, and at 
the same time using a short root piece, a poorer stand of trees and a 
slower growth takes place as compared with trees grown from equally 
long scions and root pieces or from short scions and long root pieces. 
In order to test the influence of the depth of planting the union 
of grafts upon the occurrence of disease, two experiments were con- 
ducted in independent plat 1 (see pp. 77-78). In the first experiment 
root grafts were made with scions 63 inches and roots 34 inches in 
length, and these were planted with the union 6 inches beneath the 
surface of the soil. An equal number of grafts of each variety were 
made with the scions 34 inches and the roots 64 inches long and planted 
with the union 24 inches below the surface of the soil. Sixty-four 
varieties of trees were used. Scions and roots from the same lot were 
used by the same workmen for making up each variety. They were 
planted in 1905. One-half of the trees were dug that year, taking 
every alternate tree, and the remainder in 1906, at the ages of 1 and 
2 years, respectively, with the results shown in Table III, in the 
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