DESCRIPTION OF PLATES. 
PuiaTE I. Frontispiece. Fig 1.—A 2-year-old York Imperial apple tree diseased with 
the hard form of crown-gall. This tree was planted in orchard 1 and is typical of 
the most seriously diseased trees planted in the experimental orchards. Fig. 
2.—A 2-year-old Ben Davis apple tree diseased with the woolly-knot form of 
hairy-root. This tree was planted in orchard 4 and is typical of many of the trees 
in this orchard. 
PuateE II. Fig. 1.—Two seedling apple trees diseased with the soft form of crown-gall. 
These were grait- inoculated with pieces of live soft crown-galls from the roots of 
rose bushes before they were planted out. Fig. 2.—Two seedling apple trees dis- 
eased as those in figure 1, except that they were inoculated with pieces of live soft 
galls from the roots of raspberry plants. Fig. 3—Two yearling Wealthy apple 
trees diseased with the hard form of crown-gall. These trees were grown from 
root grafts, and the galls formed on the scion portion of the trees above the union 
of the scion and root pieces. Fig. 4.—A 2-year-old root-grafted York Imperial 
apple tree diseased with the hard form of crown-gall on the lower end of the scion. 
Fig. 5.—The same form of disease as that shown in figuresland 2 ona 2-year-old 
a7, OW: ealthy apple tree in which the gall surrounds the union. 
PuateE III. Fig. 1.—Yearling apple tree diseased with the simple form of hairy-root. 
These are ‘typical of the: seedlings used in the experiments with this form of the 
disease. Fig. 2.—A 2-year-old Jonathan apple tree diseased with the broom-root 
form of hairy-root, from cooperative plat 3. Fig. 3.—A healthy, smooth-rooted 
apple tree, typical of those planted in orchards 1 to4. Fig. 4.—A healthy seedling 
apple tree with an excess of fibrous roots, but not a trace of either crown-gall or 
hairy root. 
Priate IV. Fig. 1.—An early stage of the aerial form of hairy-root at the base of a ter- 
minal bud on a Charlamoff apple-tree twig. Fig. 2—Another portion of the same 
twig, showing the knot that formed during each of the preceding years at the base 
of the terminal bud. Fig. 3.—Early stage of the aerial form of hairy-root at the 
base of buds on a much larger limb of the same tree from which the twigs shown 
in figures 1 and 2 were taken. 
PLATE V. Fig. 1.—Mature stage of the aerial form of hairy-root on a limb of a Winesap 
seedling apple tree. Fig. 2.—Another diseased limb of the same tree, showing a 
development oi roots (woolly-knot) from some of the knots after the limb had been 
placed in a moist chamber for two weeks. 
PuaTe VI. Fig. 1.—A longitudinal section of a grafted apple tree through a soft crown- 
gall 2 months old, formed on the lower end of the scion of a poorly fitted root erat 
in an experiment. Fig. 2.—An early stage in the development of the simple form 
of hairy-root, showing the origin of roots from the base of buds on a yearling apple 
seedling when placed in moist sand in early springtime. Fig. 3.—A later stage in 
the development of the same form. Fig. 4.—An older stage of the simple form of 
hairy-root, showing how the small roots dry up and become hair-like. It was from 
this form that the disease received the name “hairy-root.’’ Fig. 5.—A longitu- 
dinal section through a Wealthy apple tree diseased with the woolly-knot form of 
hairy-root. Both the tree and the knot are 2 years old, the latter originating in a 
wound, as indicated by the dark line in the tissues beneath the knot. Fig. 6—A 
longitudinal section through a hard crown-gall on a 2-year-old Wealthy apple tree, 
showing the origin of the gall from the lower end of the scion. 
PrATE WIL Pigvile ~The root of a seedling apple tree grown from a cutting taken from 
a seedling apple tree diseased with the simple form of hairy-root. Fig. 2.—The 
root of a Charlamoff apple tree grown from a root graft, the scion of which was taken 
from a tree diseased with the aerial form of hairy-root. Both this and the former 
tree show only traces of the woolly-knot form of the disease and were exceptionally 
vigorous trees. Fig. 3.—Roots of a yearling Fameuse apple tree grown from a 
root grait made from a healthy scion united with a root piece diseased with the 
simple form of hairy-root. The scion has thrown out healthy roots. This is 
typical of the varieties of apple trees which root readily from the scion. Fig. 4.— 
Roots of a Jonathan apple tree grown similarly to the previous one. This tree has 
not thrown out roots from the scion and is typical of those varieties of apple trees 
which do not root readily from the scion. 
186 
98 
ee a 
