- 
- 
Crown-Gall in the Apple Nursery 5 
sponding lot of trees resulting from untreated grafts which were 
used as checks. The variety used in each case was Summer 
Rambo. In both illustrations the galled trees are on the left, the 
doubtful trees in the middle, and the clean trees on the right. 
Figure 7 shows a lot of Ben Davis trees selected as a sample of 
some of the best results obtained from grafts treated with the 
mercury compound, and Figure 8 shows the corresponding lot of 
Ben Davis trees resulting from untreated grafts used as checks. 
Reading from left to right, in both illustrations, it will be seen 
that there were no galled trees grown from the treated grafts, as 
compared with 48 galled 
trees in the check lot. 
This, of course, represents 
an example of absolute 
control that has not been 
met with very often in the 
experiments. 
DISCUSSION 
Recently Riker and 
Keitt + have advanced the 
working hypothesis that 
“the malformations dealt 
with in the rejected nur- 
sery trees were not induced 
by the crown-gall organ- 
ism.” This hypothesis 
was formulated because of 
their negative results in 
attempts to isolate the or- 
ganism from 175 trees 
which had been rejected 
on account of malforma- 
tions supposedly due to 
crown gall. Since appar- 
ently similar malforma- frig. 5.—one of the lots of trees which, after 
} 2 classifying, represented approximately the 
tions WEKE not only con average of results obtained with the organic 
trolled SRS VAS but also ee aan’ etek cede y Pe 
ambo. Reading from left to right: Galle 
were largely prevented trees (5), doubtful (11), clean (77) 
from forming by the ac- 
tion of germicides in the writers’ experiments, their results are not 
in accord with the hypothesis of Riker and Keitt. It is difficult to 
assume that these malformations are due to any agency other than 
a pathogenic organism, since they are so definitely prevented by 
germicices. 
Referring to Riker and Keitt’s statement that malformations 
occur on grafts treated as aseptically as possible and “that gall- 
like formations may develop without the intervention of Bacterium 
zumefaciens,” attention is called to the fact that Hedgcock? per- 
1 Riker, A. J., and Keitt, G. W. Crowngall in relation to nursery stock. Jn Science, 
vol. 62, p. 184-185. 1925. 
2 Hedgecock, G. G. Field studies of the crown-gall and hairy-root of the apple tree. 
U. S. Dept. Agr., Bur. Plant Indus. Bul. 186, 108 pp., illus. 1910. 
