20 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE. 
root form of hairy-root. This result is considered representative of 
the relative proportion of each form of the disease occurring upon 
1, 2, and 3 year old trees in the Mississippi Valley during 1905, 1906, 
and 1907. 
Development on budded trees —No experiments were conducted on 
budded trees in the nursery. Observation made at the time of dig- 
ging indicated that although budded trees develop much less crown~- 
gall than root-grafted trees, there is often a considerable develop- 
ment of the forms of hairy-root. This may in part be due to the 
poor grade of seedlings which are often planted for the purpose of 
budding. 
RELATIVE DEVELOPMENT OF EACH FORM OF THE DISEASE IN THE 
ORCHARD. 
Four orchards were planted and studied during the present inves- 
tigation. In addition, observations were made of the trees in a 
number of orchards grown by others. The trees in experimental 
orchards 1 and 2 (for conditions of experiment see pp. 38 and 57 in 
the appendix) were dug at the close of the period of investigation, 
at which time they were 8 years old. Notes were taken on the con- 
dition of the roots of each tree in these orchards when it was planted 
in the orchard and again at the time of digging. Out of 234 apple 
trees that were healthy when transplanted into the orchards, 153, or 
65.4 per cent, remained healthy; 23, or 9.8 per cent, died; 11, or 4.7 
per cent, developed traces of the hard form of crown-gall; and 47, 
or 20.1 per cent, showed traces of the woolly-knot and aerial forms 
of hairy-root. Out of 235 apple trees diseased with crown-gall at 
the time of transplanting to the orchards, 73, or 31.1 per cent, 
entirely recovered from the disease; 30, or 12.8 per cent, died; 63, 
or 26.8 per cent, were diseased with the hard form of crown-gall; 
and 69, or 29.3 per cent, developed the woolly-knot form of hairy- 
root, chiefly from the surface of former hard galls. 
The results of the experiment, briefly stated in another form, are 
these: Traces of the hard form of crown-gall developed on 4.7 per 
cent of the healthy trees, but none of the soft form was found. 
Traces of hairy-root, chiefly of the woolly-knot form, developed on 
20.1 per cent of the healthy trees. Nearly a third of the trees (31.1 
per cent) diseased with the hard form of crown-gall recovered; al- 
most another third (29.3 per cent) developed the woolly-knot form 
of hairy-root from the hard form of crown-gall; and the remaining 
trees (31.1 per cent) were still diseased with the hard form of crown- 
gall, which had not developed as rapidly as the growth of the trees. 
Orchard 1 contained both budded and root-grafted trees. Four 
rows of healthy trees grown by budding were planted near four rows 
186 
