Crown-Gall in the Apple Nursery 7 
Since this disease is 
caused by a germ easily 
killed by germicides when 
it can be reached and since 
this germ may be present 
over the surface of the 
) roots, the problem of kill- 
i) ing the organisms present 
on the surface and of dis- 
infecting the material re- 
solves itself into the ques- 
tion of finding a suitable 
germicide or fungicide and 
a suitable dosage which 
will kill the bacteria and 
not materially injure the 
roots of the trees. In this 
respect the organic-mer- 
cury compound, used as a 
dip in these experiments, 
represents a distinct im- 
provement over the for- 
Fic. 7.—Lot of Ben Davis trees selected as show- 
maldehyde solution. ing some of ee lees pete neh a control- 
ing crown ga y the use of the organic- 
Well-made grafts prop- mereury compound. Reading from Jett to right: 
: 7 alled trees (none in this case), doubtful (1), 
erly fitted, especially those cette: 
which have no overhang 
at the lower end, were shown by Hedgcock to be less susceptible 
to crown gall. ‘They have, in fact, less exposed callus. The wrap- 
ping, of course, should be thoroughly done, whatever method is 
selected. Since the material 
has to be handled so much 
and since the freshly made 
grafts will stand this disin- 
fectant, part of the writers’ 
experiments also included 
dipping the grafts the same 
day they were made, in 
order to disinfect and satu- 
rate the wrappers with the 
germicide and to give a 
second coating to the grafts 
themselves. 
Since there is still a pos- 
sibility after the grafts have 
been stored and the young 
tender callus developed that 
this may carry incipient in- 
fections and as it is desir- 
able to give another dose of 
the germicide just before 
Fic. 8.—Trees from untreated Ben Davis grafts planting, a third dipping 
grown as checks for the lot illustrated in Was tried and found to be 
Figure 7. Reading from left to right: Galled 
trees (48), doubtful (4), clean (61) noninjurious to the graft 
