6 Department Circular 376, U. S. Dept. of Agriculture 
formed almost identical experiments over 15 years ago and arrived 
at the following significant conclusions: ““The two regions where 
the formation of callus in root grafts was most abundant * * * 
coincide exactly with the position of more than 90 per cent of the 
galls, * ™ * indicating a close relation between the formation 
of callus and the development of the disease.” All of the writers’ 
observations and experiments furnish additional evidence to sup- 
port these conclusions of Hedgecock. 
It should also be noted that the failure to find a parasitic organism 
or agency in diseased tissue at any given time does not necessarily 
justify the conclusion that the organism or agency is not present or 
that it has not been present 
at some previous. time. 
Until conclusive evidence 
is brought forth proving 
that malformations “sup- 
posedly crown gall” are 
not due to the strongly 
pathogenic organism Bac- 
tertum tumefaciens Sm. 
and Tn., the present rigid 
inspection and rejection of 
crown-gall trees should be 
maintained. It is consid- 
ered that this particular 
question is of vital impor- 
tance to the orchardist. 
RECOMMENDATIONS FOR 
CONTROL 
Seedling apple trees of 
l-year’s growth ordinarily 
show a certain amount of 
hairy root and crown gall. 
These seedling trees with 
si 4 s 
Fic. 6.—Lot of untreated Summer Rambo trees either type of the disease 
grown as checks for those shown in Figure 5. when lined out for budding 
Speer (Gy, enn ae Galledwerees 29)7) or whem sed wor erafting 
continue to carry the dis- 
ease, in the great majority of cases at least. The experience of the 
writers is that the apple-seedling growers inspect the seedling stocks 
rather critically. Only an occasional gall and a few hairy-root trees 
may escape their scrutiny. However, when these diseased stocks are 
planted out or cut up into pieces for piece-root grafting, the nursery- 
man is simply propagating the disease. The best practice, therefore, 
is to inspect critically the seedling stocks before using them for 
grafting and to burn all the obviously infected ones. It has been 
generally accepted by both pathologists and nurserymen, at least since 
the work of Hedgcock, that the selection of roots free from crown- 
gall and hairy-root infection is an important factor in the control of 
this disease. 
