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Crown-Gall in the Apple Nursery 3 
grafts. This proved to be the case. In a number of experiments 
performed in 1925 complete ¢onfirmation of results of experiments 
initiated in 1921 with the formaldehyde solution and in 1923 with the 
organic-mercury preparation has been obtained. In practically all 
of these experiments the grafts were wrapped either with raffia or 
with a cheap grade of muslin in such a manner as to cover completely 
the graft unions. The trees were dug as 1-year grafts. Neither the 
stand nor the amount of growth was reduced by the use of the or- 
ganic-mercury compound as compared with untreated grafts grown 
as checks. The trees were classified into three grades: (1) Galled 
trees, with further subdivision into those with large and those with 
small galls; (2) doubtful trees, that is, trees exhibiting symptoms so 
slight as to be open 
to question or differ- 
ence of opinion; and 
(3) clean trees, that 
is, those trees which 
showed no symptoms 
of gall or hairy-root. 
It should be stated 
that practically all 
of these so-called 
doubtful trees would 
have been classed as 
clean trees in an or- 
dinary _inspection. 
The accompanying 
illustrations were 
made from _ photo- 
graphs of trees 
grown in the experi- 
ments of 1925. Fig- 
ure 1 illustrates ex- 
amples of clean 
trees. Figure 2 il- 
lustrates the type of 
tree which has been gre. 2.—Type of tree classified as possessing a small gall 
classified as possess- 
ing a small gall, whereas Figure 3 illustrates two types of trees classi- 
fied as having large galls, which have invariably encircled over 40 
per cent of the circumference of the tree. Figure 4 represents one of 
the types of trees classified as doubtful. 
TABLE 1.—Comparison of results obtained with all. grafts treated with the 
organic-mercury compound and untreated grafts grown as checks 
Treated grafts . Untreated grafts 
| Percentage of galls Percentage of galls 
Number Number 
Large Total Large Total 
eRe si a ei es Se oe 2.0 Giele 2 GLO eer een ee Tae 28. 7 | 32. 6 
