56 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE. 
apple trees inserted into slanting incisions in the roots and tied 
with grafting thread. One set was prepared about six weeks before 
planting and kept dormant by being stored in moist excelsior in a 
cool place; the other was prepared in the same way as the first and 
planted out immediately. For each set an additional set of-an 
equal number was wounded and wrapped with thread without 
inoculating. All were grown one year. Of the inoculated stored 
seedlings, 7.4 per cent became diseased with crown-gall; of the 
control, 4.3 per cent, chiefly of the hard form; of the inoculated set 
planted immediately, 34.1 per cent became diseased with crown- 
gall, chiefly of the soft form; and of the control, 2.9 per cent, chiefly 
of the hard form. 
In a second experiment, 500 root grafts were prepared from healthy 
scions of Wealthy grafted healthy seedling roots as a control set. 
A similar set of 500 grafts was prepared by rubbing the tongued end 
of both the scion and the root pieces on the freshly cut surface of a 
living soft gall from an apple tree before joining together the cut, a 
number of galls being used. These were planted in the nursery after 
being stored for six weeks in separate boxes in a cool cellar. At the 
end of one season’s growth there was approximately the same amount 
of disease in the control as in the inoculated sets, the control ‘con- 
taining about 19.5 per cent of trees diseased with crown-gall, and, 
the inoculated set 21 per cent, both chiefly of the hard form. | 
The results of the these experiments indicate that the communica- 
tion of crown-gall to wounds in apple trees is a variable factor and 
that the contact of wounded living galls with wounded surfaces 
when dormant may result in little or no infection, but that under | 
erowing conditions, where callus is formed abundantly, such as 
resulted at once where the seedlings were inoculated with pieces of 
living apple galls and planted immediately, the disease was com- 
municated readily. In these seedlings growth, with the formation 
of callus, took place at once, favoring the entrance of the organism. 
In the case of the stored seedlings and grafts, owing to the low temper- 
ature, the formation of callus was retarded at least one month before 
it became warm enough for its development. 
In the writer’s opinion, given in the light of the results of these 
and other experiments recorded in this bulletin, crown-gall is com- 
municable by contact only in wounds where fresh callus is being 
formed. Where trees are dormant there is little danger of communi- 
cation. 
The disease only slightly communicable in orchards.—Reference will 
again be made to orchards 1 and 2, already described. <A statement 
of the condition of the trees in these orchards at the beginning of the 
186 . 
