46 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE. 
From the preceding citations, which are representative, it is appar- 
ent that the opinions of plant pathologists, with few exceptions, 
have been as follows: 
(1) Apple crown-gall spreads rapidly in the nursery and the orchard 
from tree to tree. 
(2) It may be communicated from diseased to healthy trees by 
contact, in bundles, etc. 
A review of the literature on the subject reveals that little has been 
done previously in the way of experimentation to substantiate these 
views as to the degree and the rapidity of the spread of the disease 
in the nursery and the orchard. 
PREVIOUS PUBLICATIONS ON THE COMMUNICABILITY OF HAIRY-ROOT. 
The previous citations bore upon the communicability of crown- 
gali, but i most cases the statements made no separation of crown- 
gall from hairy-root, both types of disease being included under the 
term “ crown-gall.”’ 
Stewart, Rolfs, and Hall (64), who first described hairy-root of 
the apple, did not express their opinion as to the communicability 
of the disease, but regarded it as separate and distinct from crown- 
gall. 
EXPERIMENTS ON THE COMMUNICABILITY OF THE DISEASE. 
Studies on the formation of callus as related to crown-gail.—In order 
to study the relation of callus to wounds an experiment was prepared 
with a number of sets of apple cuttings, seedlings, and root grafts. 
Some of the cuttings were made with blunt or square ends, others 
with slanting or pointed ends. Some were cut with longitudinal 
incisions, some with spiral incisions, and some with cross incisions 
through the bark and cambial layer; others lacked such incisions. 
The seedlings were washed clean, sterilized for five minutes in a one- 
tenth per cent water solution of corrosive sublimate, and again 
washed in boiled water. They were cut off at both ends, roots and 
shoots, to the length of 9 inches. The root grafts were made of the 
tongue or whip-graft pattern, some closely fitted, some poorly fitted, 
others with the upper end of the root cut off bluntly, and others with 
the lower end of the scion cut off in the same manner. 
The materials were prepared for the experiment the Ist of Febru- 
ary, the usual time for root grafting at the larger nurseries in the 
Mississippi Valley. The cuttings, seedlings, and root grafts of each 
pattern were tied for storage in bundles in the same manner as root 
grafts are tied for storage at nurseries. They were divided into two 
equal series, one of which was stored in a cool cellar at a temperature 
186 
