SUMMARY. 71 
and much more abundant on root-grafted trees. Hairy-root of the 
simple form is frequent on apple seedlings and on budded and root- 
grafted trees. The woolly-knot form of hairy-root is the most 
common form of the disease, especially on 3-year-old root-grafted 
trees in the nursery and on orchard trees. The broom-root form 
occurs occasionally on trees grown on loose soils. 
Crown-gall of both forms develops chiefly the first year on seed- 
lings and root-grafted trees in the nursery. It gains entrance almost 
entirely through wounds. On root-grafted trees it occurs most com- 
monly on the lower end of the scion at the union. In the experiments 
less crown-gall was found on nursery trees the second and third years 
than the first, which is strong evidence that it ceases to develop to 
any great extent. Hairy-root develops on root-grafted trees to some 
extent the first two years, and to a less extent the third. 
In the experiments varying the depth of planting the union had 
little effect on increasing or decreasing the amount of disease present 
in apple trees grown from root grafts, but a better stand of trees was 
obtained by the shallower planting of the union. Very little difference 
was shown in the amount of disease resulting from the use of the 
upper half and the lower half of seedling roots for making root grafts. 
An increase of both crown-gall and hairy-root occurred in root- 
orafted trees when apparently healthy scions or roots were taken from 
trees otherwise diseased. The use for making root grafts of roots 
from apple seedlings diseased with the simple form of hairy-root 
resulted in an increased stand of trees in the nursery, but also in a 
large percentage of inferior trees diseased with hairy-root of the simple 
form. The disease did not as a rule extend from the root to the scion 
portion of the tree during the three years of growth in the experiment. 
Cuttings from seedlings diseased with this form of hairy-root usually 
sent out roots more readily than healthy cuttings and often developed 
into vigorous-growing trees. 
Where scions for root grafts were taken from yearling trees and 
from bearing trees in the orchard, no great difference in the number 
of healthy trees obtained from either was noted, but there was a slight 
increase of disease in the trees from the scions taken from yearling 
stock, 
Leaving a bud near the lower tip of the scion did not increase the 
disease in trees grown from root grafts. No great difference in the 
amount of disease present in trees from root grafts was noted where 
seedlings grown from both French and American seed were used. 
The results, however, were decidedly in favor of stock grown from 
American seed, since the stand of trees with the latter was 25 per cent 
better. 
186 
