DEVELOPMENT OF FORMS OF THE DISEASE. 25 
thirds of the trees grown on the hairy-root pieces would be graded 
as culls, especially those grown from the Jonathan, the Scott Winter, 
and the Wolf River varieties, and the use of such seedlings for grafting 
must be condemned, the same as those diseased with crown-gall. 
In these experiments a careful count was made by the writer of 
he number of trees diseased with each form of crown-gall and hairy-: 
root. -In the first series of experiments, of the 3,976 trees grown from 
erafts made from seedlings diseased with hairy-root of the simple 
form, 0.5 per cent was diseased with the soft form and 6.8 per cent 
with the hard form of crown-gall, while 69.1 per cent was diseased 
with the simple form, 5.2 per cent with the woolly-knot form, and 2.8 
per cent with the broom-root form of hairy-root. Of the 2,864 trees 
erown from grafts made from seedlings with smooth roots, 0.7 per 
cent was diseased with the soft form and 11.9 per cent with the hard 
form of crown-gall; and 2.8 per cent was diseased with the simple 
form, 4.1 per cent with the woolly-knot form, and 3.3 per cent with 
the broom-root form of hairy-root. 
Increased development of the disease due to the use of seedlings diseased 
urth crown-gall in making root grafts.—In connection with the previous 
set of experiments (see Table VII, in the appendix), in addition to 
the two sets of root grafts prepared for that experiment, a third set 
was prepared in which the same stock of scions on root pieces cut 
from seedlings diseased with the soft form of crown-gall was used. 
Care was taken in each case to cut away the portion of the root con- 
taining the origin of the gall, so as to use the apparently healthy 
portions of the roots. These root grafts were made, planted, and 
erown with those in the previous experiment, the same set of root 
grafts beimg used for a control. The results of the experiment are 
given in Table VIII, in the appendix. 
The results of this experiment prove that the use in making root 
grafts of apparently healthy root pieces from seedlings diseased with 
soft crown-gall increases the amount of the disease, the increase in 
this case amounting on an average to 12.9 per cent of crown-gall and 
2.3 per cent of hairy-root or a total of 15.2 per cent. 
In some nurseries workmen do not always discard seedlings diseased 
with crown-gall, but cut away the galls and use the remaining portion 
of the root, as was done in the experiment just given. Such a prac- 
tice must be condemned, since it increases considerably the develop- 
ment of the disease in root-grafted trees. 
The slight effect of using for root grafts scions from younger and older 
trees—An experiment was conducted to determine the effect on 
the development of crown-gall and hairy-root of grafts made with 
scions taken from fruiting orchard trees as commenced with those 
made with scions taken from yearling trees in the nursery. Two 
186 
