AN APPLE STEM-TUMOR NOT CROWNGALL 1 
By NmiB A. Brown 
Pathologist , Laboratory of Plant Pathology , Bureau of Plant Industry , United States 
Department of Agriculture 
There are many kinds of apple-tree outgrowths or stem deformities; 
some are due to winter injury, some to weak variety conditions, some 
trees have short internodes, others, swellings of internodes or nodes. 
The type referred to in this paper as stem-tumor is the outgrowth with 
masses of rootlike projections or, as it occurs on some varieties of apple 
trees, an outgrowth with a smooth or nearly smooth surface. The out¬ 
growths vary in size from small warts (PI. 2, A) to tumors 2 to 6 inches 
in diameter, though they project scarcely more than one-half inch beyond 
the surface of the stem (PI. 1, G). On some trees the bark remains 
comparatively smooth and the tumors do not reach a breadth of more 
than two or three inches (PI. 3, B); but usually the bark breaks and 
masses of aborted roots appear, giving a roughened budlike surface to 
the outgrowth. The tumors of the bud type increase in size readily 
and in time the bark may become black and rough and broken if the 
tree is a very susceptible one. This may extend along an entire limb 
(PI. 2, C). The budlike type is the more common. 
These tumors are similar in macroscopic details to tumors produced 
by artificial inoculation with pure cultures of Bacterium tumefaciens. 
Furthermore, crowngall and hairy-root are widely prevalent on apple 
trees. Accordingly, although some entomologists 2 have referred to 
infestation by woolly apple aphis as capable of resulting in galls or warty 
swellings on twigs, limbs or trunk of apple trees, nursery inspectors, 
nurserymen, orchardists, plant pathologists and entomologists have in 
general referred to this type of outgrowth as aerial crowngall. How¬ 
ever, this so-called aerial crowngall, of which Plate 1, A, is a good repre¬ 
sentation, is seldom, if ever, caused by the crowngall organism under 
natural conditions. _ 
Since 1906 the writer has been concerned with crowngall on various 
hosts and during this period the attempts to isolate Bacterium tumefaciens 
from apple stem-tumors always have been unsuccessful, but as the tumors 
resembled the hairy-root type of crowngall as it occurs on apple roots it 
was believed that the disease was a form of crowngall. In 1923 the writer 
began a more critical study of the disease. 
Some of the material used was received from several different States, 
and some of it was collected near Washington by the writer, so that 
there was ample material in good live condition for the platings. 
Platings were made from tumors just starting to form, and in all stages 
of growth and development, the largest being 6 inches in diameter. 
1 Received for publication Dec. 20, 1923. 
2 'Rarer. A. C. the woolly apple aphis. U..S. Dept. Agr. Rpt. 101, p. 34 * * 9 * 5 * 
Journal of Agricultural Research, 
Washington, D C. 
VoL XXVII, No. 9 
Mar. 1, 1924 
Key No. G-378 
81990—24 
(69s) 
6 
