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Bul. 186, Bureau of Plant Industry, U. S. Dept. of Agriculture. ; PLATE |

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FIG. 2.—WoOOLLY-KNOT FORM OF HAIRY-ROOT OF THE APPLE.

Fig. 1.—HARD FORM OF CROWN-GALL OF THE APPLE.

U. S. DEPARTMENT OF AGRICULTURE,
BUREAU OF PLANT INDUSTRY—BULLETIN NO. 186.

B. T. GALLOWAY, Chief of Bureau.

FIELD STUDIES OF THE CROWN-GALL AND
HAIRY-ROOT OF THE APPLE TREE.

BY

GEORGE G. HEDGCOCK,

PATHOLOGIST, FRUIT-DISEASE INVESTIGATIONS.

IssuED NOVEMBER 17, 1910.

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WASHINGTON:
GOVERNMENT PRINTING OFFICE.

O10.

BUREAU OF PLANT INDUSTRY.

Chief of Bureau, BEVERLY T. GALLOWAY.
Assistant Chief of Bureau, G@. HAROLD POWELL.
Editor, J. E. ROCKWELL.

Chief Clerk, JAMES E. JONES.

FRUIT-DISEASE INVESTIGATIONS.
SCIENTIFIC STAFF.
Merton B. Waite, Pathologist in Charge.
W.M. Scott and C. L. Shear, Pathologists.
W.S. Ballard, L. A. Hawkins, George F. Miles, F. V. Rand, J. W. Roberts, and J. M. Shull, Assistants.
Clara H. Hasse, Laboratory Assistant.
Leslie Pierce, Special Agent.

186
2

LETTER OF TRANSMITTAL.

U.S. DEPARTMENT OF AGRICULTURE,
BUREAU OF PLANT INDUSTRY,
OFFICE OF THE CHIEF,
Washington, D. C., April 15, 1910.

Str: [I have the honor to transmit herewith a manuscript entitled
“Wield Studies of Crown-Gall and Hairy-Root of the Apple Tree,”’
by Dr. George G. Hedgecock, at present Pathologist in Investigations
in Forest Pathology.

This paper embodies the results of several years of ceetientan
and experiment and covers the distribution of crown-gal! and hairy-
root, a description of their different forms, their probable relations,
and their development; the effect of the diseases upon apple trees;
the susceptibility of varieties; communicability in the nursery and
orchard; and prevention and cure. The paper marks the comple-
tion of Doctor Hedgcock’s work on this subject. The field study
of these diseases will be continued by the Office of Fruit-Disease
Investigations.

Studies of the etiology and interrelations of crown-gall have been
made by Messrs. Smith and Townsend and by Miss Brown, of the
Bureau of Plant Industry, and are still in progress.

I respectfully recommend that this manuscript be published as
Bulletin No. 186 of the series of this Bureau.

Respectfully, ear
a GATE LO WAN:

Chief of Bureau.
Hon. JAMES WILSON,
Secretary of Agriculture.

Go

186

CONE Nan Sy

HMEROCATChIOMMrery ete ear ck Ns el ne ere ey Rei ayesha) ena
iElistoricalenotes on crown-gall'and hairy-root---5....2-.2..--.--5----...4.---:
Distribmtionto® the disease and related forms: ...2.2....:....-...............

Geoorap nica idistributionss .: Gaeta eee = re ie ee
ID IStEUO ML ONBINSINUITSeEICSs tens {eee cee nee one a elon ee a

Description of the different forms of the disease on apple trees..............--

OEMS OMChO wile tet ee Se el eh eps Meee cies cue 2 Pk pans
SONG Crowne ae eee a ts el pei eas 0 ae Reet meir Beet oi a0 2
TE LBMRGL GIRONA TRESS Se eae ha aes cee mn cass pg ee At a Ra
IBOKIMSIOlMMANKV TOOL sa eas. fogs hee ine epee ea ae eee
PS UUT AN ONS S Uo) eo aah airs ah wy are 8 rel Ne Grae deans
Woolly Skat Ob etO ri see se ica ee beta ee oe eS
BTOOM-FOOG LOMMi seat Se ea is ae ee ee i nee eae

Relation of sott;crowm-gall tohard crown-gall:-.-.5..-.-2.5....2..5----:*
Relation or Malky-root toxcrowm-Calli=. 2495 an 9 ig
Relationsof theorms of hairy-root to each) other! ...225-5 222-5... sae.

Development ofthe formsvotthediseases:+.25255-- 25-0852 52 552525. 2a Sea.

No development of the disease on seedlings without wounds..............-
Greenhouse experiments with uninjured seedlings...................
Greenhouse experiments with wounded seedlings....................
Nursery experiments with young seedlings.........:...........--...-
Nursery experiments with older seedlings.......-.::.........--.....--

Relative development of the disease on budded and root-grafted trees in

EMOMMMINS CI peer te ae Sener s Sees ee ya ee
Bevelopment-on-budded. trees: ....... 25.2. 82.52 2-225. sses eee e-
Development on-root-erafted trees. .........-.:2..- 22.2 22 222-2-se525-

Relative development of each form of the disease in the nursery.......-..-.
Development on_root-gratted trees:.-2.--..-.2-.--2-222.252+242-eeeee-
Developmentron: budded. treess <2 cans. . sees yee se se

Relative development of each form of the disease in the orchard..........

A study of nursery methods in root grafting as related to the development

Gin CRG CAS Cait ote e fone st Cee eee Ae ae see ye a

The slight effect from using different portions of seedling roots in root
EIEN MNOS SEER eA eR en Men ume re tee he ees Pr ass ue
Increased development of the disease due to the use of seedlings
diseased with hairy-root in making root grafts...............-------
Increased development of the disease due to the use of seedlings
diseased with crown-gall in making root grafts.............--.------

186 5

15

6 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

Development of the forms of the disease—Continued.

A study of nursery methods in root grafting, etc —Continued.

The slight effect of using for root grafts scions from younger and older

No effect from leaving a bud near the lower end of the scion in making
root grafts... 2.22.2 setae eee eee eee ee
Experiments comparing American and foreign-grown apple seedlings.
The use of seedlings from old nursery districts for making root Ba
may not increase the development of the disease........... :
Heavy, wet soils favor the development of crown-gall in the nursery -
Period for the maximum development of crown-gall and hairy-root in
the nursery 2.222. 22 eee i ee ee

Effect of the disease upon apple trees=- = 4 22— 2-5 oe ee
Observations by others onjerown-call= 2]. 2222 ee
Observations by othersion hairy-root.- 222-2 ----5---
Experiments on the effect of the disease on apple trees.........--.....---.

Effect ontseedlings not uniionm = 3 - Sa. 2 ote eae eee
Slight. effect on grafted trees in the nursery ..-.-.._..---.-2-2__4.__-
Little or no effect on orchard trees shown in experiments....-.....-..
Experments:bysothers sees eae gee Jaa Nests ae aS
Experimental orchards 522. ee ee

Susceptibility of varieties of apple trees to the disease...........--....--.--.-
Data upon a number of common varieties used in experiments.........--.
Susceptibility of scions grown in different localities.....................-

Communicability of the disease in the nursery and the orchard.............--
Previous publications on the communicability of apple crown-gall....._..
Previous publications on the communicability of hairy-roct.............-
Experiments on the communicability of the disease. ...........--.-...--

Studies on the for.aation of callus as related to crown-gall..-.........-
Studies on root formation as related to hairy-root....-.--....--..-----
No communication of the disease to healthy uninjured seedlings......
The disease is communicable to wounded seedlings.....-..-.......--
Increase of the disease in root-grafted trees due to the inoculation of

grafts... 2... ee 2. i a ee ee
Increase of the disease due to poorly fitted root grafts............--.-.
The use of scions from diseased trees increases the amount of disease. .
The spread of the disease from tree to tree in nursery rows is almost

negligible after the first years-2 = 95.2 ie ee
Pruning and the grafting knives are not responsible for much of the

disease... . 2. 2225.9 .22 Re ee ee eee
Crown-gall not readily eoueninnnceies to dormant trees stored in

bundles... =: 2.22224: 51225 So Sa
The disease only slightly communicable in orchards............--..-

Prevention and cure... 2:5... 23. gee ee
Probable futility of attempts at preventiom==25-= === = eee
Methods for the control of the disease in nursery bins........--......-----
Propagation of susceptible varieties of apple trees by budding.-....... baee
Improvement in methods of reoteraftings.- 9) a ee

186

Selection of healthy scions mecessaryea--) eee
Selection of healthy seedling roots mecessary--........-2...--..-.-_--
Careful fitting of root grafts neeessanyce === ae ee ee

' Page.

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CONTENTS.

Prevention and cure—Continued.

Improvement in methods of root grafting—Continued.
Experiments on the best methods of wrapping root grafts..........---
Nira ppineswith cloth... 2. seen jee oe Cee eg (en
NWiirap pli maa Gh rub betas aia etree, ee penis emma iaay Ge
Witappineswith: Waxed: paper: ohne tes Wachee ey alee gett at
Wirappinerwith: plane thread 33. 52sc em geier laaees eaten win etm 8
Wrappimeswath waxed: thread: scsi: tess 0s ee eee ree
Witaxsimoct he: UM1ONsS 5. onee eee eas eeera Oe mae ae trey caret
Wimgrap pinot e Tatts hac yee na Seven mine ere RES
VESTS Ole SPERIMeMtsas a= seas Ane Nate ees Ls ene ae ene
Hatenexperiments 1m wrapping root crafts... 22220. 222. te. 2
The use of weak antiseptics for the prevention of disease in root grafts of
ombtiibevalieGes sms tee eine ee ce Sete ee Ca eee
a ekun caamcestOnine FOO oTalts: ss 222" sacs ao oe een
SIT ELOIaLAINGINe TOOt Chaltseae. <n wee ay eee eyes Se Rae aay ae, oh es
Careinethe culiivation-of trees im the nursery. -.2.-.252..-.2..-2222.1-.:
Selection of healthy trees for the scion orchard necessary..-.....--.------
Selection of the best kinds of soil for growing trees.............----------
Cure of diseased trees in the orchard........-- Highs re ace eth RO MR Pca aS
EXMenimM EnitseoVyaO (MOTs Soo. wie ety. Stan is a eet te ae eee
Recommendations for the treatment of the disease in orchards...-...--
STUDIO Ace Sean eS SST SS Bie GLI E Bey Ieee ek eis lee eee er ae Gea
Nec ommMen dations: = cea rienin bas ee Ae aD Sora Sue ee a

APPENDIX.

Methods and conditions of experimentation in the study of crown-gall and hairy-

IB EXe MIME ise tirecOTCCMMOUSCL A.) S20 a ne pee ee ay a ere ie ei cee
RSapenimentselnataenMultseLry sac 0c i a0 2s ot ee eee eg ece eye Sees
Imdependentmursernyaex periments... 2.1 a0 eee oe ee ee ee
Cooperative mursery experiments... ..22 22.22... -2 = ee ee

EPXeMe HIM MUSPIMAORCMALASeescincen <a Piao. ola esse ORS es eae ee eee:
Tables giving the results of experiments in the study of crown-gall and hairy-

PONG. BSR: TAG) LAVAS ISN UEP, eI a eae ere Ss on aps
Ai eal LNOMIRO MOR ee a Sore sc, Se ie ee cle 22 a oe cep ee Ae

PLATE I.

1B Es

Ill.

TV:

Wal

VALE:

Vid:

ILLUSTRA PIONS:

Fig. 1.—Hard form of crown-gall of the apple. Fig. 2.—Woolly-knot

Page.

form. of hairy-root.of the apple) = 5 = Frontispiece.

Fig. 1.—Soft form of crown-gall of the apple, from inoculation with
rose galls. Fig. 2.—Soft form of crown-gall of the apple, from inoc-
ulation with raspberry galls. Fig. 3.—Hard form of crown-gall on
the scion portion of root-grafted apple trees. Fig. 4.—Hard form of
crown-gall at the lower end of the scion in a root-grafted apple tree.
Fig. 5.—Hard form of crown-gall surrounding the union in a root-
erafted apple tree: 2.22, oa en Se SS eee

Fig. 1.—Simple form of hairy-root on apple seedlings, typical of those
used in the experiments. Fig. 2.—Broom-root form of hairy-root on
a 2-year-old apple tree. Fig. 3.—Healthy root-grafted apple tree,
showing the type of the healthy trees planted in the experimental
orchards. Fig. 4.—Healthy seedling apple tree with fibrous roots.

Fig. 1.—Early stage of the aerial form of hairy-root on an apple twig.
Fig. 2.—Later stage of the aerial form of hairy-root on the same twig
as that shown in figure 1. Fig. 3.—Early stage of the aerial form
of hairy-root on an older limb of the same tree as that from which
the twigs shown in figures 1 and 2 were taken...........---....--

. Fig. 1.—Mature stage of the aerial form of hairy-root on a Winesap

seedling apple tree. Fig. 2.—Root production from the aerial form
of hairy-root on a limb from the same tree as that from which the
limb shown in figure © was:takencs. 422 o-etee ee
Fig. 1.—Radial section through a soft crown-gall in an apple root
graft. Fig. 2.—Early stage of the simple form of hairy-root on an
apple seedling. Fig. 3.—A later stage in the development of the
same form as that shown in figure 2. Fig. 4.—An older stage of the
simple form of hairy-root, many roots being hair-like. Fig. 5.—
Radial section through a woolly knot originating in a wound on the
scion of a root-grafted apple tree. Fig. 6.—Radial section through
a hard crown-gall originating on the lower end of the scion ofa
root-grafted apple tree.) 2 S22 222 see ee
Fig. 1.—Root of an apple tree grown from a cutting taken from a seed-
ling apple tree diseased with the simple form of hairy-root. Fig. 2.—
Root of a grafted apple tree grown from ascion taken from a diseased
limb of the tree twigs and a limb of which are shown in Plate IV.
Fig. 3.—Roots of a Fameuse apple tree grown from a root graft with
the root piece diseased with hairy-root, but with healthy roots on
the scion. Fig. 4.—Roots of a Jonathan apple tree grown from a
root graft diseased with hairy-root, but with no roots on the scion.
Fig. 1.—Apple root grafts showing nine kinds of wrapping used in the
experiments. Fig. 2.—Root grafts left too long in storage, showing
excessive development of callus. = 2-3 = = ee

. Fig. 1.—The woolly-knot form of hairy-root on the crown of a Collins

apple tree in orchard 1. Fig. 2.—Apple root grafts and seedlings
used in the experimentg®: 22. (362 oe eee

. Typical rows of trees in orchard 1: A, A row of Collins apple trees dis-

eased with the hard form of crown-gall when planted in the orchard;

B, a row of the same variety, planted at the same time, but with

healthy roots... .. 2... 2 2S he See ee eee
186
8

100

100

100

100

100
100

100

100

B. P. 1.—580.

FIELD STUDIES OF THE CROWN-GALL AND HAIRY-
ROOT OF ithe AP Th En.

INTRODUCTION.

Growers of fruit trees have noted for many years a diseased con-
dition of apple trees which usually manifests itself on young trees
in the formation of galls and of clustered or fasciated roots at or near
the surface of the ground, and on older trees in the form of knots
or tumors occurring on the branches. These forms of disease have
been variously designated as ‘‘galls,”’ “crown-gall,” ‘“crown-knot,”’
“hairy-root,”’ ‘woolly-knot,” ‘woolly-root,” “broom-root,” ‘root
knots,” “‘root galls,’ and “‘tumors.”’

In recent years these forms of the disease have been brought promi-
nently before the public by a number of investigators. As a result of
the consequent agitation, following statements alleging their danger-
ous nature, many States have enacted stringent laws for prevention
and control. Although such laws, as a rule, should be enacted as a
matter of precaution, in this case they have entailed great hardship
and loss tonurserymen. An estimate of this loss, based upon reports
received from leading wholesale nurserymen in various parts of the
country, places the amount at not less than half a million dollars
annually. The actual loss to orchardists is uncertain. In fact, data
from exact and careful orchard experiments have not hitherto been
available.

A very unsatisfactory condition has arisen from the widely diver-
gent opinions of observers relative to the communicability of crown-
gall and to its effect. State laws upon the control of these forms of
disease vary as much as the opinions of those who have made observa-
tions upon their effect. Consequently, there has arisen an urgent de-
mand from nurserymen and horticulturists for more exact data on
their nature. In response to this demand, a series of studies and ex-
periments, embracing the greater portion of the United States, has
been conducted by the writer for a continuous period of seven years.
This investigation has included the forms of disease ordinarily known
as “crown-gall” and “hairy-root” attacking many kinds of trees,
vines, and shrubs, embracing a study of the cause, communicability,
effect, and extent of the various forms of disease.

186 9

10 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

This bulletin embodies the results of that portion of the investiga-
tion which relates to apple® trees. An endeavor is made to set forth
clearly the nature of the disease and its effect upon trees in the nur-
sery and the orchard, as well as to reeommend methods for its con-
trol in the orchard. Of no less importance is the information for
nurserymen resulting from a large number of experiments in nursery
practice. Methods are given whereby loss caused by some forms of
crown-gall and hairy-root may be either lessened or almost completely
eliminated without greatly increasing the cost of growing trees in the
nursery. Finally, it is shown by actual experiment that in the case
of the milder and usual forms of the disease little or no injury is ap-
preciable in young orchards. More intense forms, however, may be
injurious, but in an orchard these rarely develop from the milder
forms. No proof has been found that any of the forms are beneficial,
as in case of the root tubercles of legumes.

The writer has briefly described in this and in previous publica-
tions a number of forms of crown-gali and hairy-root. There remain
some points of doubt to be cleared up by other investigators, since
this publication concludes the writer’s work on this subject. In the
discussion which follows, for reasons given later and in order not to
confuse the reader, all forms of crown-gall and hairy-root will be con-
sidered as forms of the same disease.

The results of many experiments are given, some of which were con-
ducted in Missouri, Illinois, Iowa, Nebraska, Kansas, and Arkansas,
and others in the District of Columbia and Virginia. It is necessary,
for brevity, to say in the beginning that all experiments were prepared
and conducted under the personal supervision of the writer and that
all portions of each experiment were equally well prepared and cared

for under similar conditions. Where such is not the case mention

is made of the fact. |

In the index to literature, on pages 93 to 96 of this bulletin, are cited
all of the principal publications on apple crown-gall and hairy-root
published in the United States, as well as many of those in other
countries. A number of American and foreign publications on the
subject of crown-gall deal with the disease on other hosts than the
apple, and these have not been cited.

Prior to July, 1907, the work of investigation was conducted in the
Mississippi Valley Laboratory of the Department of Agriculture at
St. Louis, Mo., under the supervision of Dr. Hermann von Schrenk.

@ Owing to the confusion in the nomenclature of many of the common varieties of
apples, all of the names used in this bulletin are in accordance with the ‘‘ Nomenclature
of the Apple,’ by W. H. Ragan, Bulletin 56, Bureau of Plant Industry, issued January
25, 1905.

186

HISTORICAL NOTES. Aah
HISTORICAL NOTES ON CROWN-GALL AND HAIRY-ROOT.

The forms of the disease originally known as ‘‘crown-gall,” con-

- sisting of fleshy outgrowths on the roots of fruit trees, have been

known by nurserymen to occur in the United States for nearly half
a century, although the first published mention of them is much later.
In fact, about all the literature on the subject dates since 1890. No
one can be certain as to the time of the first appearance of the disease
in this country. In the opinion of the writer it was introduced with
plants from Europe. The Europeans have known the disease, or a
similar one, for many years. According to Sorauer (57 “) the Wurzel-
kropf, which may be considered the same disease, occurs on the apple
and the pear in Germany.

Owing to its wide geographic distribution, crown-gall has attracted
the attention of a number of investigators in this country. Bailey
(5) and Stewart (62) in New York; Clinton (8) in Connecticut; Selby
(49) in Ohio; Taft (65) in Michigan; Woodworth (79), Wickson (77),
and W. E. Smith (56) in California; Toumey (68) in Arizona; Forbes
(10) in Illinois; Alwood (1) and Phillips (40) in Virginia; and E. F.
Smith (53), E. F. Smith and Townsend (54), von Schrenk (71), and
Hedgcock (19) of this Department have published articles concerning
the crown-gall forms of the disease. Others are cited later in this
bulletin.

The forms of the disease known as hairy-root have been observed
by some of the older nurserymen ever since they have grown apple
trees, dating back nearly fifty years. Attention was first called to
the disease in this country by Stewart, Rolfs, and Hall (64). In 1900
they described the simple form of hairy-root on apple seedlings in
New York, giving it the name “‘hairy-root,’’ which had already been
applied to the disease by nurserymen. This form and three other
forms of the disease have since been recognized and described by the
writer (21).

In Europe at least two forms of the disease have been described
by German investigators. That known in Germany as ‘“ Wurzel-
krop{” is apparently identical with crown-gall. Frank (14) and
Sorauer (58) have described this disease on the apple and the pear.
A second form of the disease in Germany, which is apparently iden-
tical with the aerial form of hairy-root, is called ‘‘Kropfmaser” by

Frank (14) and Sorauer (61). Kissa (30) describes this disease on

Pirus malus sinensis. Julie Jaeger (28) describes the same disease on
the limbs of apple trees. Wakker (74) describes a similar disease on
species of Ribes in Holland.

@ The numbers in parentheses used in this paper refer to the index to literature on
pp. 93-96. -
186

12 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

DISTRIBUTION OF THE DISEASE AND RELATED FORMS.
GEOGRAPHICAL DISTRIBUTION.

The hard and soft forms of crown-gall on the apple tree and on
various other plants have either been observed by the writer or
reported to him by others in practically every State in the Union.
The writer has found both forms of the disease on apple trees in every
locality where nurseries were inspected by him, and in many where no
nurseries were located. The disease, in both forms, is most abundant
in the more southern States of the apple-growing belt, from Virginia
to Texas. The writer collected data in 31 States and Territories and
received reports of occurrence from correspondents in all of the others
except Nevada.

In Europe, as previously mentioned, crown-gall or a similar disease
(Wurzelkropf) occurs on apple and pear trees in Germany. The
writer finds it common on apple seedlings imported direct from Hol-
land and France. W.S. Blair, in a letter, reports its occurrence in
Ontario, Canada, on apple trees.

The forms of the disease known as hairy-root have been found as
widely disseminated as crewn-gall on apple trees in nurseries and
orchards in the United States. In orchards hairy-root is more com-
mon than crown-gall.

In Europe the aerial form of hairy-root or a similar form (Kropf-
maser) occurs on apple trees in Germany (60). W. S. Blair, by
letter, reports the occurrence of hairy-root on the roots of apple trees
in Ontario. Hairy-root of the simple and of the woolly-knot form has
been found by the writer on trees imported into the United States
from New Zealand.

DISTRIBUTION IN NURSERIES. ~

In seedling nurseries apple trees are grown for one season from seed,
then dug and used for propagation in budding and root grafting.
The writer inspected the stock at the time of digging in a number of
the largest seedling nurseries in Kansas, Nebraska, Iowa, and Mis-
sourl. In one lot of 300,000 apple seedlings examined, sorted, and
and counted under his supervision, less than one-half of 1 per cent
was diseased with crown-gall, almost entirely of the soft form, and
about 1 per cent with hairy-root, chiefly of the simple form. This
percentage holds good for all of the nurseries examined.

In nurseries where trees are propagated by budding and root grait-
ing, as compared with seedling nurseries, there is a much greater per-
centage of disease. On trees grown from root grafts there is more
disease than on those propagated on seedlings by budding. The rela-
tive percentage of disease of each form found on budded and grafted

trees in nursery experiments is shown on pages 18 and 19.
186

DIFFERENT FORMS OF THE DISEASE. lis

DESCRIPTION OF THE DIFFERENT FORMS OF THE DISEASE ON
APPLE TREES.

FORMS OF CROWN-GALL.

The: term ‘“crown-gall”’ as used in this bulletin applies to the
fleshy outgrowths, or galls, occurring rarely on the stems and fre-
quently on the crown and the roots of apple trees. It is applied only
to those galls that are not accompanied by an excessive formation of
either roots or incipient roots and are not caused by insects. Two
forms have been recognized by the writer—the soft and the hard (19).

Soft crown-gall.—The term “soft crown-gall’’ has been applied to
the form most frequently found on young seedling, grafted, and
budded apple trees (Pl. II, figs. 1 and 2). These galls consist at first
of a soft, succulent growth of young cells thrust out from the cam-
bial layer of roots or shoots. They commonly originate in wounds
and their initial growth is quite similar to that of an enlarged cailus
(Pl. VIII, fig. 2), which they resemble in form, color, and structure.

‘The surface of the galls, owing to an unequal growth of the elements

in the tissues, soon becomes coarsely convoluted. Curled and dis-
torted masses of wood cells and vessels are gradually formed through-
out the softer tissues, often causing the galls to become hard and
woody in the interior. At first the color of the surface is white, but
later it either changes to the color of the adjacent healthy tissues or
becomes brown or black from the decay of the surface cells, which at
no time are protected by an epidermis.

In size these galls usually vary from that of a pea to that of a man’s
fist, but in exceptional cases they may grow to the size of a man’s
head. They do not develop roots from their surface, and under
natural conditions in the nursery they generally decay at the end of
the growing season. In general appearance and structure they
resemble the crown galls of the almond, apricot, blackberry, cherry,
chestnut, grape, peach, pear, plum, raspberry, rose, and walnut, to
which they are related (22).

Hard crown-gall.—The term ‘“‘hard crown-gall’’ has been applied
to the form occurring more frequently on older trees in nurseries and
orchards (PI. II, figs. 3, 4, and 5). The earlier growth of these hard
galls is similar to that of soft crown galls, but later they become cov-
ered with bark and develop a woody interior. They finally have a
texture intermediate between that of healthy wood and that of soft
crown galls. Roots often spring from their tissues and they thus
develop into a form of hairy-root (see p. 57). Unlike the soft galls,
they do not decay, but continue their growth the following season.
The hard galls finally attain the same size as the soft galls, but are
much slower in their development. They usually have a more finely
convoluted surface and are of the same color as the adjacent healthy

186

14 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

tissues. During each period of new growth the bark of the hard
galls is usually ruptured, only to be re-formed at the close of the
eTrowing season.

FORMS OF HAIRY-ROOT.

The term “‘hairy-root’’ as used in this bulletin is a general term
applying to four closely related forms of the disease occurring on
shoots and roots of apple trees. In these there is an increased and
abnormal production of either roots or incipient roots. Four forms
have been recognized: The simple, the woolly-knot, the broom-root,
and the aerial.

Simple form.—The term ‘‘simple hairy-root’”’ has been applied to
the form of hairy-root originally described by Stewart, Rolfs, and
Hall (64) (PI. III, fig. 1). This form is the common one on apple
seedlings, but occurs less frequently on grafted and budded apple
trees in the nursery and the orchard. It consists of numerous small
roots growing out at nearly right angles, either singly or in tufts, from
an older root or stem (PI. VI, figs. 2, 3, and 4). This root formation
takes place from adventitious buds in the cambial layer, either directly
from a root or stem or from swellings thereon. Such roots from the
first are more succulent than normal ones. The cells of the par-
enchyma are hypertrophied and the formation of wood cells is
retarded. On exposure to air such roots dry up and become hair-
like in appearance.

Woolly-knot form.—A second form, which has been called ‘ woolly-
knot,” is infrequent on young apple seedlings, but common on older
seedlings and on grafted and budded trees in nurseries and orchards.
This form originates as follows: A smooth, irregular swelling
develops, usually in a larger root near the surface of the soil. This
projects at first half an inch or so from the surface of the root. Mean-
while, in the interior of the swelling an incipient root formation takes
place. In a few months this usually develops to such an extent that
it breaks through the epidermis, producing a warty knot. Under
favorable growing conditions, during either the same or succeeding
years, there is thrown out from each root center on the surface of the
knot a rapid-growing, succulent root, which resembles in develop-
ment and structure those of the simple form. Many roots usually
develop from a single knot. These are often fasciated, and through
intricate branching develop into a great mass of fine roots (PI. I,
fig. 2). This form may develop from hard crown-galls. (See p. 57.)

Broom-root form.—A third form of hairy-root occurs frequently on
budded and grafted trees in nurseries in States bordering on the
Missouri River. It consists of a broom-like formation of fine roots,
occurring usually at the end of a side root which otherwise appears

186

¢

DIFFERENT FORMS OF THE DISEASE. ES

healthy (PI. III, fig. 2). Frequently a broom-root springs from a
root which has its origin in a hard crown-gall. Broom-roots resemble
those of the woolly-knot in structure, and they develop in much the
same way, except that they do not originate directly in swellings, but
develop by the excessive branching of root ends. They usually
grow upward from their point of origin toward the surface of the soil,
in contrast with normal fibrous roots, which grow more nearly
parallel to the surface.

Aerial form.—A fourth form of hairy-root, which also has been
called ‘‘stem tumors”’ (22), occurs on the trunks and limbs of apple
trees, more commonly on older trees in orchards. This form con-
sists at first of smooth, fleshy swellings (Pl. IV, figs. 1, 2, and 3) in
which the cambial layer is much thickened. These swellings are
more or less rounded, but are often irregular in outline, vary in width
from half an inch to 2 or 3 inches, and project from a half inch to an
inch beyond the surface of the tree. They develop, internally, incip-
ient adventitious roots, which as the disease progresses break forth,
throwing off the outer bark and forming a warty knot (PI. V, fig. 1).
Cuttings containing the disease in its earlier stages readily throw out
roots when placed in moist sand or soil in the springtime, developing
directly into the woolly-knot form of the disease (PI. V, fig. 2). On
orchard trees as the knot grows older the incipient roots in the center
of the knot die, and in some cases new ones are formed in the adja-
cent healthy tissues, increasing the diameter of the knots but not
their projection.

RELATIONS OF THE FORMS OF THE DISEASE TO EACH OTHER.
RELATION OF SOFT CROWN-GALL TO HARD CROWN-GALL.

The work of Smith and Townsend (54) in discovering and demon-
strating that Bactervum tumefaciens is the cause of the crown-galls of
the Paris daisy, the peach, etc., and the work of Townsend with the
same or a similar organism from the galls and hairy-root of apple
trees indicate that all of the forms of the disease may be caused by
the same species of bacterium or some of its forms.”

Since the soft and the hard forms of crown-gall are alike in their
initial development and since the latter may develop from the former,
the two thus differing only in the final form and in duration, it follows

that they both may be due to the same cause. It may be that in

the case of the hard form the apple tree partially resists the organism
causing the disease by healing over the surface of the galls and con-
fining the disease to limited areas, and the soft form may be a more
virulent type of the disease.

@ See also Smith, Erwin F., Science, n. s., vol. 30, no. 763, August 13, 1909, p. 223.
186

16 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

RELATION OF HAIRY-ROOT TO CROWN-GALL.

Smith, Townsend, and Brown have isolated from hairy-root a bac-
terlum with which they have reproduced the disease on the sugar
beet and on the apple. It has not yet been proved that the hairy-
root forms of disease may be produced by inoculation of apple trees
with Bacterium tumefaciens, unless the two organisms Smith, Town-
send, and Brown have isolated are identical, but the production of
these forms is not morphologically impossible. In the orchard
experiments described on pages 38 and 57 it was noted that a con-
siderable number of the trees diseased with hard crown-gall developed
hairy-root from the galls.

RELATIONS OF THE FORMS OF HAIRY-ROOT TO EACH OTHER.

The forms of hairy-root are closely related to each other, the essen-
tial feature of each consisting of an excessive development of roots,
evidently the result of the same sort of stimulus acting upon dormant
root centers or buds in the twigs and the trunk of the tree in the ease
of the aerial form, upon root buds on the main roots in the case of the
simple and woolly-knot forms, and upon the side roots in the case of
the broom-root form. The woolly-knot form is directly related to
the hard form of crown-gall (see p. 20).

European investigators of these forms of disease have always con-
sidered the crown-gall (Wurzelkropf, tuberculosis) a different dis-
ease from the aerial tumors or the aerial form of hairy-root (Kropf-
maser, broussin). As the identity is not completely established, these
forms will be treated separately in the experimental data recorded,
and all data will be given under.the separate forms as hairy-root and
crown-gall. :

DEVELOPMENT OF THE FORMS OF THE DISEASE.
NO DEVELOPMENT OF THE DISEASE ON SEEDLINGS WITHOUT WOUNDS.

Greenhouse experiments with uninjured seedlings—In experiments
conducted in pots and beds in the greenhouse with uninjured seed-
lings grown directly from seed (see p. 77), 102 apple seedlings kept
free from wounds remained healthy, showig no traces of crown-gall
or hairy-root. Of 48 apple seedlings grown under similar conditions,
except that the surface layers of soil were mixed with finely chopped
pieces of living hard and soft apple galls after the seed had germinated,
none became diseased.

Greenhouse experiments with wounded seedlings—In connection
with the experiments mentioned in the preceding paragraph, 98 apple
seedlings were grown under the same conditions as the first lot, with-

out soil inoculation. When they were 2 months old each was
is

[or

DEVELOPMENT OF FORMS OF THE DISEASE. it

wounded on the root just below the surface of the soil with a sterile
knife. In each case the cut extended upward and through the
cambial layer. The blade of the knife was sterilized in a 1-to-1,000
solution of mercuric chlorid before each cut was made. Four seed-
lings became diseased with small, hard galls, which formed from out-
growths from the cambial layer on the upper edge of the wound. All
other wounds healed normally. No formation of hairy-root occurred.

Nursery experiments with young seedlings.—In the nursery it is
quite impossible to grow seedlings entirely free from injuries. To
ascertain to what extent wounds favor the develapment of crown-
gall and hairy-root, 100 consecutive trees in a nursery row were
wounded by a knife cut in the cambial layer, just below the surface
of the soil. These trees were about 2 months old when wounded.
For a control, the same number of consecutive trees in an adjacent
row were selected, in which no wounds were made. At the end of
the growing season the trees in both rows were dug. Of the wounded
trees, 3 died. Of the remaining wounded trees, 8 were diseased with
soft crown-gall, 2 with the simple form of hairy-root, and 2 with the
woolly-knot form. Of the control trees, 1 was diseased with soft
crown-gall and 2 with the simple form of hairy-root. Thus, four
times as many wounded as unwounded trees became diseased.

The percentage of diseased trees in apple-seedling nurseries is
usually small. In exceptional cases only is it considerable, no doubt
due to injuries received by the young trees during the first two or
three months of their growth. ‘This is certainly true in the case of
the development of crown-gall, and may apply also in that of hairy-
root.

In order to ascertain the relation of wounds to the various forms
of crown-gall and hairy-root, 300 diseased yearling apple seedlings
were selected, as follows: 100 with soft crown-gall, 50 with hard
crown-gall, 100 with the simple form of hairy-root, and 50 with the
woolly-knot form of hairy-root. These were dissected to ascertain
the presence of wounds in the roots at the time that the disease
attacked the seedlings. Such injuries are indicated by the presence
of a small discolored rift, showing a break in the tissues near the
heart of the tree beneath the outgrowth of the diseased portion.
Certain indications of wounds were found under 90 of the soft galls,
47 of the hard galls, and 22 of the woolly-knots. In the case of most
of the trees diseased with simple hairy-root, there were discolored
areas which were not considered rifts or breaks in the tissues. On
the whole, there was decided proof that the first three forms just

named are quite closely connected with injuries to the young roots.

Nursery experiments with older seedlings.—In a field experiment at
Louisiana, Mo., 350 apple seedlings were transplanted and grown
50414°—Bul. 186—10——2 3

18 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

under ordinary nursery conditions. One-half of the trees, taking
alternate trees in each row, were dug at the end of one year after
transplanting, and the remaining trees at the end of two years. In
transplanting, the taproot of each seedling was cut off. Table I, in
the appendix to this bulletin, gives the results of the experiment.

Twenty trees died from the effects of transplanting. It will be
noted in Table I that there was an increase of crown-gall amounting
to 0.8 per cent the first year and 0.1 per cent the second year after
transplanting. At the same time there was an increase of 8.6 per
cent of hairy-root the first year, and a decrease of 2.3 per cent the
second year.

No experiment was made with seedlings grown from seed in which
the trees were allowed to grow in the original place of planting for
longer than a year. Nurserymen assert that there is little or no
increase of disease after the first year, and that where seedling trees
have been pulled with a tree puller at the age of 10 years in the
seedling nursery there is no greater percentage of disease present
than during the first year. :

RELATIVE DEVELOPMENT OF THE DISEASE ON BUDDED AND ROOT-
GRAFTED TREES IN THE NURSERY.

Development on budded trees.—In the propagation of varieties of
apple trees by budding, seedlings at-the age of 1 year are tipped;
that is, the taproot is cut off. Then they are planted in rows in the
nursery. These are budded the following summer. The slit in the
bark where the bud is inserted is just above the surface of the soil.
Crown-gall of both forms usually develops, if at all, at the two points
where wounds are made, i. e., at the place where the bud was
inserted and at the tip of the root. As arule, much less crown-gall
develops on trees propagated by budding than on those propagated
by root grafting. Hairy-root develops more frequently than crown-
gall on budded apple trees. The simple and the woolly-knot forms
are common, the former developing on portions of the root below
the surface of the ground and the latter at or near the surface, often
from the region of the wound made in budding.

Development on root-grafted trees—In the propagation of apple
trees by root grafting, whether by whole roct or piece root, more
extensive wounds are necessarily made than are usual in budding.
Wounds occur at the point of union where the scion piece is spliced
to the root piece—at the lower end of the scion piece and at the upper
and lower ends of the root piece.

Crown-gall, both soft and hard, like callus, develops usually at two
points in the root graft—the lower end or tip of the scion piece (PE

VI, figs. 1 and 6) and the lower end of one root piece. More than 90
"186

2

DEVELOPMENT OF FORMS OF THE DISEASE, 19

per cent of the galls ordinarily develop at the former point. An ex-
ception occurs with some varieties, like the Wealthy, which are sus-
ceptible to the hard form of crown-gall and woolly-knot. Such varie-
ties often develop the disease from the scion above the union (PI. II,
M23).

It was found in experiments where the seedlings used for root graft-
ing were carefully selected and only smooth roots used that hairy-root
of the simple form was nearly eliminated. Such was not the case
with the woolly-knot form.

It is asserted by. practically all of the nurserymen from whom data
have been collected, and the list includes nearly all of the large grow-
ers of apples in the United States, that apple trees propagated by
budding yearling transplanted seedlings are as a rule much freer from
both crown-gall and hairy-root than root-grafted trees.

Reports have been received from a number of nurseries giving the
number of diseased trees among budded and root-grafted trees grown
under similar conditions. These are combined and given in Table II,
in the appendix.

From Table II it will be noted that-there is a decrease of 3 to
39 per cent of disease on budded trees as compared with root-grafted
trees. Thisis representative of the reports received. Two exceptions
not given in the table must be mentioned: One occurred in Utah, the
other in Virginia. In these two instances budded trees were reported
badly diseased with crown-gall.

Under the conditions that generally prevail in the Central and
possibly in the Eastern States, propagation by budding is advised at
least in the case of varieties susceptible to erown-gall and woolly-knot.
Owing to the fact that it takes one season longer to propagate an apple
tree by budding than by root grafting, 1t will be more profitable to
use the latter method of propagation in such States as California,
where an apple tree is easily grown for market from root grafts in one
season.

RELATIVE DEVELOPMENT OF EACH FORM OF THE DISEASE IN THE
NURSERY.

Development on root-grafted trees—In all of the larger nursery
experiments records were kept of the number of apple trees diseased
with each form of crown-gall and hairy-root. In the set of experi-
ments conducted on cooperative plats 1 to 8 (see p. 78), 50,472
trees were grown from root grafts made from healthy scions and
seedlings. Of these trees, 77.2 per cent was healthy, while 0.6 per cent
was diseased with the soft form and 13.3 per cent with the hard form
of crown-gall; with 2.6 per cent diseased with the simple form, 3.5
per cent with the woolly-knot form, and 2.8 per cent with the broom-

186

20 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

root form of hairy-root. This result is considered representative of
the relative proportion of each form of the disease occurring upon
1, 2, and 3 year old trees in the Mississippi Valley during 1905, 1906,
and 1907.

Development on budded trees —No experiments were conducted on
budded trees in the nursery. Observation made at the time of dig-
ging indicated that although budded trees develop much less crown~-
gall than root-grafted trees, there is often a considerable develop-
ment of the forms of hairy-root. This may in part be due to the
poor grade of seedlings which are often planted for the purpose of
budding.

RELATIVE DEVELOPMENT OF EACH FORM OF THE DISEASE IN THE
ORCHARD.

Four orchards were planted and studied during the present inves-
tigation. In addition, observations were made of the trees in a
number of orchards grown by others. The trees in experimental
orchards 1 and 2 (for conditions of experiment see pp. 38 and 57 in
the appendix) were dug at the close of the period of investigation,
at which time they were 8 years old. Notes were taken on the con-
dition of the roots of each tree in these orchards when it was planted
in the orchard and again at the time of digging. Out of 234 apple
trees that were healthy when transplanted into the orchards, 153, or
65.4 per cent, remained healthy; 23, or 9.8 per cent, died; 11, or 4.7
per cent, developed traces of the hard form of crown-gall; and 47,
or 20.1 per cent, showed traces of the woolly-knot and aerial forms
of hairy-root. Out of 235 apple trees diseased with crown-gall at
the time of transplanting to the orchards, 73, or 31.1 per cent,
entirely recovered from the disease; 30, or 12.8 per cent, died; 63,
or 26.8 per cent, were diseased with the hard form of crown-gall;
and 69, or 29.3 per cent, developed the woolly-knot form of hairy-
root, chiefly from the surface of former hard galls.

The results of the experiment, briefly stated in another form, are
these: Traces of the hard form of crown-gall developed on 4.7 per
cent of the healthy trees, but none of the soft form was found.
Traces of hairy-root, chiefly of the woolly-knot form, developed on
20.1 per cent of the healthy trees. Nearly a third of the trees (31.1
per cent) diseased with the hard form of crown-gall recovered; al-
most another third (29.3 per cent) developed the woolly-knot form
of hairy-root from the hard form of crown-gall; and the remaining
trees (31.1 per cent) were still diseased with the hard form of crown-
gall, which had not developed as rapidly as the growth of the trees.

Orchard 1 contained both budded and root-grafted trees. Four
rows of healthy trees grown by budding were planted near four rows

186

DEVELOPMENT OF FORMS OF THE DISEASE. Pit

of healthy trees of the same varieties grown by root grafting. Of
27 budded trees planted, 5 became diseased, all with traces of the
woolly-knot form of hairy-root. Of 31 grafted trees, 3 became dis-
eased with traces of woolly-knot and 1 with the hard form of crown-
all.

In the results of these and other experiments in orchards 3 and 4,
the following facts are prominent: That of the healthy trees trans-
planted, about the same proportion became diseased as is usual
in the nursery, but only with traces of the disease, consisting mainly
of hard crown-gall and woolly-knot; that nearly a third of the trees
diseased with the hard form of crown-gall recovered; that the soft
form of crown-gall may develop into the hard form; and that the
hard form of crown-gall in many instances developed into the woolly-
knot form of hairy-root.

A STUDY OF NURSERY METHODS IN ROOT GRAFTING AS RELATED TO
THE DEVELOPMENT OF THE DISEASE.

The slight effect of varying the depth of planting the union in root
grafts.—The effect of deep planting upon gall and hairy-root forma-
tion has been a matter of much discussion among nurserymen and
others. Howard (24) concludes from experiments “that the gall
develops least where the root is long, thus causing the point of union
between the scion and stock to be near the surface of the ground.
Especially is this true of clay soil.”

A number of wholsesale nurserymen growing apple trees on a large
scale assert that little benefit is gained by using short scions and long
roots, and that a happy medium of length between the two is best.
If a long scion is used, placing the union too deep in the soil, and at
the same time using a short root piece, a poorer stand of trees and a
slower growth takes place as compared with trees grown from equally
long scions and root pieces or from short scions and long root pieces.

In order to test the influence of the depth of planting the union
of grafts upon the occurrence of disease, two experiments were con-
ducted in independent plat 1 (see pp. 77-78). In the first experiment
root grafts were made with scions 63 inches and roots 34 inches in
length, and these were planted with the union 6 inches beneath the
surface of the soil. An equal number of grafts of each variety were
made with the scions 34 inches and the roots 64 inches long and planted
with the union 24 inches below the surface of the soil. Sixty-four
varieties of trees were used. Scions and roots from the same lot were
used by the same workmen for making up each variety. They were
planted in 1905. One-half of the trees were dug that year, taking
every alternate tree, and the remainder in 1906, at the ages of 1 and
2 years, respectively, with the results shown in Table III, in the

186

22 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

appendix, in which all forms of disease, both crown-gall and hairy-
root, are combined. A large increase of hairy-root, but not of crown-
gall, was noted the second year. |

The second experiment was made with five varieties, Northwestern
Greening, Grimes, Duchess, Walbridge, and Ben Davis, grafted on
seedling roots of the same stock. The same number of grafts of each
variety was made in two equal sets, one with scions 6 inches and
piece roots 4 inches in length, the other with scions 4 inches and roots
6 inchesin length. The former were planted with the union 5 inches
below the surface of the ground, and the latter with the union 3 inches
below the surface. An equal number of each set and of each variety
were planted in cooperative plats 1 to 8 (see p. 78). A definite
proportion of the trees, selected in a numerical series in the rows, was
dug each year for three years, at the ages of 1, 2, and 3 years, respec-
tively. The results are shown in Table IV, in the appendix, in which
the number of trees and the percentage diseased with crown-gall and
hairy-root are given.

From the results of these two experiments (see Tables III and IV)
it will be noted that there was an actual increase of the disease in the
case of the shallower planting of the union, in the first experiment
amounting to 6.5 per cent and in the second to 2.5 per cent. The
greatest development of crown-gall took place the first year and of
hairy-root the first and second years. If the results of the two
experiments be combined by adding the number of healthy and
diseased trees in each, the result is 19.2 per cent of diseased trees
where the union was planted deeper and 22.2 per cent where planted
shallower, or a difference of 3 per cent in favor of the deeper planting
of the union. This, however, is much more than offset and the
practical results of the experiment are reversed by the fact that 13.2
per cent more trees were raised when planted shallowly than when
planted deeply, or, in other words, there was a gain of 10.2 per cent
by planting the union 24 to 3 inches below the surface of the soil as
compared with planting it 5 to 6 inches deep.

The slight effect from using different portions of seedling roots in root
grafting.—In making piece-root grafts the root of the seedling tree is
cut into two or more pieces. The opinion has been expressed by
nurserymen that when the upper or collar piece of the seedling root
is jomed to a scion in a root graft there will be a greater prevalence
of disease than when the lower or middle piece is used. In order to
test this assumption a series of experiments was conducted in which
equal numbers of grafts were made on the collar or upper pieces of
the seedling roots and on the tip or lower pieces of the roots. Scions
from five varieties of apples—Northwestern Greening, Walbridge,
Grimes, Duchess, and Ben Davis—were used. These were grown in

186

:
.
‘
J

DEVELOPMENT OF FORMS OF THE DISEASE. 23

equal numbers in cooperative plats 1 to 8 (see p. 78). <A definite
proportion of these trees, selected in a numerical series,* was dug for
each of three successive years—1905, 1906, and 1907—at the ages of
1, 2, and 3 years, respectively. The combined results from the eight
plats are given in Table V, in the appendix.

The results of the experiments show an increase of hairy-root on
trees grown from grafts made on the upper pieces of seedling roots.
This is the portion of the seedling root that is most susceptible to
the simple form. This increase of disease, 3.6 per cent, was more
than offset by the greater stand of trees resulting from the use of the
upper piece root, since an increase of 408 trees, or 15.9 per cent,
was obtained. For practical purposes, then, the upper portion of
the seedling root grows the greater number of healthy trees, in spite
of the slight increase of disease. The tip pieces are smaller than the
collar pieces, and root grafts made from them, being smaller, do
not grow as vigorously as those made from collar pieces. :

Increased development of the disease due to the use of seedlings dis-
eased with hairy-root in making root grafts.—Two sets of experiments
were conducted to determine to what extent the use of seedlings
diseased with crown-gall and hairy-root would increase the develop-
ment of the disease in root-grafted trees in the nursery.

Two series of eight experiments were conducted on cooperative
plats 1 to 8. About three thousand apple seedlings diseased with
the simple form of hairy-root (Pl. IX, fig. 2, Nos. G and H), but
entirely free from galls, were selected for these experiments. Whip
or tongue grafts were made, all of the pieces of the roots from these
diseased seedlings being used. Some of these pieces from the root
tips were apparently healthy. All of the pieces from the upper or
collar pieces were diseased with hairy-root. As a control, an equal
number of root grafts were similarly made on roots from healthy
seedlings of the same diameter as the hairy-rooted seedlings selected
from the same stock. These two sets of root grafts were made
with scions from the following varieties of apple: Fameuse, Scott
Winter, Wolf River, Jonathan, and Salome. A definite proportion
of the trees grown from these root grafts was selected in a numerical
series and dug at the ages of 1, 2, and 3 years. The results of the
experiment are summarized in Table VI, in the appendix.

A second and smaller series of eight experiments was prepared
and conducted the same as the first set, except that scions were
used from the Yellow Belleflower apple. Two equal sets of grafts
were prepared from the same stock of seedlings, one set made on

aJn this bulletin the term ‘‘numerical series” means the selection of trees in
sequence, as every second tree, every third tree, etc., depending on whether one-
half, one-third, etc., of the trees were dug each year.
186

24 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

piece roots from seedlings with smooth roots and one on piece roots
from seedlings with hairy roots of the simple form. These were
grown also in cooperative plats 1 to 8. Table VII, in the appendix,
gives the combined results of the experiments.

These experiments yielded three positive results:

(1) The use of root pieces from hairy-rooted seedlings did not
increase the amount of crown-gall, since in the two sets of experi-
ments 7.3 and 2.6 per cent of crown-gall developed on trees grown
from hairy-root pieces, as compared with 12.6 and 7.3 per cent,
respectively, on trees grown from smooth-root pieces.

(2) A greatly increased stand of trees resulted from the use of
hairy-root pieces, since 4,956 trees were grown from grafts made on
such pieces, as compared with 3,802 grown from the same number
of grafts made with smooth-root pieces, an increase of 30.4 per cent.

(3) The use of hairy-root pieces resulted in an increased number
of trees diseased with hairy-root, since 77 and 83.7 per cent of the
trees grown from grafts made with such pieces were diseased with
hairy-root as compared with 10.2 and 8.9 per cent from grafts made
with smooth-root pieces.

The reason for the increased stand of trees from the root grafts on
hairy-root pieces is as follows: Since the season was dry and unfa-
vorable for the rooting of the grafts at the time of planting in the
first experiments, the hairy-root grafts rooted more readily, and, as a
results, fewer of them died and an increased stand resulted. The
results of the following experiments are given in proof of this state-
ment. It was found by a small experiment with cuttings from seed-
lings diseased with simple hairy-root that 25 per cent of such cut-
tings rooted (Pl. VII, fig. 1) and became trees in a bed in the green-
house, whereas only 5 per cent of cuttings taken from smooth seed-
lings of the same lot and planted in the same bed with the former
cuttings took root, and then feebly. This experiment was made
with 100 cuttings of each kind on an ordinary greenhouse bench
with 8 inches of soil, without bottom heat.

The trees grown from the different varieties of apples grafted on
the hairy-root seedlings behaved differently in their root formation.
Those varieties which rooted readily from the scion or stock—for
example, the Fameuse and the Salome—sent out smooth roots,
with very few exceptions, above the hairy-root piece (PI. VII, fig. 3).
Such trees very often formed a well-balanced root system from the
stock, and there followed the second year an atrophy of the hairy-root
pieces, which did not injure the tree. In the case of varieties that
did not root readily from the scion—for example, the Jonathan and
the Scott Winter—most of the roots were poorly balanced and sprang

from near the union (Pl. VII, fig. 4). On the whole, nearly two-
186

DEVELOPMENT OF FORMS OF THE DISEASE. 25

thirds of the trees grown on the hairy-root pieces would be graded
as culls, especially those grown from the Jonathan, the Scott Winter,
and the Wolf River varieties, and the use of such seedlings for grafting
must be condemned, the same as those diseased with crown-gall.

In these experiments a careful count was made by the writer of
he number of trees diseased with each form of crown-gall and hairy-:
root. -In the first series of experiments, of the 3,976 trees grown from
erafts made from seedlings diseased with hairy-root of the simple
form, 0.5 per cent was diseased with the soft form and 6.8 per cent
with the hard form of crown-gall, while 69.1 per cent was diseased
with the simple form, 5.2 per cent with the woolly-knot form, and 2.8
per cent with the broom-root form of hairy-root. Of the 2,864 trees
erown from grafts made from seedlings with smooth roots, 0.7 per
cent was diseased with the soft form and 11.9 per cent with the hard
form of crown-gall; and 2.8 per cent was diseased with the simple
form, 4.1 per cent with the woolly-knot form, and 3.3 per cent with
the broom-root form of hairy-root.

Increased development of the disease due to the use of seedlings diseased
urth crown-gall in making root grafts.—In connection with the previous
set of experiments (see Table VII, in the appendix), in addition to
the two sets of root grafts prepared for that experiment, a third set
was prepared in which the same stock of scions on root pieces cut
from seedlings diseased with the soft form of crown-gall was used.
Care was taken in each case to cut away the portion of the root con-
taining the origin of the gall, so as to use the apparently healthy
portions of the roots. These root grafts were made, planted, and
erown with those in the previous experiment, the same set of root
grafts beimg used for a control. The results of the experiment are
given in Table VIII, in the appendix.

The results of this experiment prove that the use in making root
grafts of apparently healthy root pieces from seedlings diseased with
soft crown-gall increases the amount of the disease, the increase in
this case amounting on an average to 12.9 per cent of crown-gall and
2.3 per cent of hairy-root or a total of 15.2 per cent.

In some nurseries workmen do not always discard seedlings diseased
with crown-gall, but cut away the galls and use the remaining portion
of the root, as was done in the experiment just given. Such a prac-
tice must be condemned, since it increases considerably the develop-
ment of the disease in root-grafted trees.

The slight effect of using for root grafts scions from younger and older
trees—An experiment was conducted to determine the effect on
the development of crown-gall and hairy-root of grafts made with
scions taken from fruiting orchard trees as commenced with those
made with scions taken from yearling trees in the nursery. Two

186

26 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

sets of grafts were made on the same lot of seedling roots—one from
scions selected from orchard trees 12 years old, the other from year-
ling nursery stock of the Northwestern Greening variety. These
were grown in cooperative plats 1 to 8. Table IX, in the appendix,
gives the results as tabulated each year for three years, a definite
proportion of the trees being dug each year at the ages of 1, 2, and 3
years, the trees being selected in a fixed numerical series in the row.

It will be seen from Table IX that there was an increase of 2.4 per
cent of crown-gall and of 3.1 per cent of hairy-root in the case of
trees grown from scions taken from rapidly growing yearling trees in
the nursery as compared with trees grown from scions of harder wood
taken from fruiting orchard trees. The difference, however, is more
than counterbalanced by the increased stand of trees, 7.8 per cent,
obtained from the scions from yearling trees. It must be concluded
that the difference, though small, is not in favor of the use of scions
with softer wood from young and rapidly growing trees.

No effect from leaving a bud near the lower end of the scion in making
root grafts.—It has been asserted by some of the older workers in
nurseries that the increased amount of crown-gall on the union at
the poimt or lower end of the scion is due to cutting the scions so
that a bud is left near the lower end. This matter was tested in an
experiment, with the result that the assertion was found to be
without facts to support it.

In this experiment scions from the variety Jonathan were cut in
two ways: One set was made without a bud at the lower end of the
scion, another equal set with a bud in close proximity to it. These
were grafted on healthy seedling roots of the same lot and planted in
ordinary soil in independent plat 1 (see p. 77). Two lots of one hun-
dred root grafts of each kind were planted. Of the trees grown from
grafts with buds on the lower ends of the scions, 19.2 per cent were
diseased, and of the trees grown from those without buds, 21.1 per
cent were diseased, showing positively that the bud has no direct
influence in increasing the amount of disease.

Experiments comparing American and foreign-grown apple seed-
lings.—There exists in many localities the opinion that seedlings
erown from foreign seed are less apt to develop crown-gall and hairy-
root than those grown from American seed. To test this theory, two
equally large sets of grafts were prepared, scions from the following
varieties of trees being used: Maiden Blush, Winesap, Baldwin,
Yellow Transparent, and Missouri. One set was grafted on seedlings
grown from apple seed imported from France, the other on seedlings
of the same grade grown in the same field from American apple seed.
The grafts were divided into eight equal lots and planted in coopera-

tive plats 1 to 8. A definite proportion of the trees, selected in a
186

DEVELOPMENT OF FORMS OF THE DISEASE. Dat

numerical series, was dug each year for three years. Table X, in the
appendix, gives the combined results of the experiment.

The results of the experiment were in favor of the use of American
seed for growing seedlings, since there was an increase of 4.9 per cent
of crown-gall on the trees on roots grown from French seed, and, on
the other hand, an increase of 1.3 per cent of hairy-root on trees grown
from roots from American seed. If we combine the number of trees
diseased both by crown-gall and hairy-root, there will be found an
increase of 3.6 per cent of disease, due to the use of French seed.
This difference is further accentuated by the number of trees grown
from the same number of grafts on the roots from American seed, 2,255
as compared to 1,802 on roots from French seed, or a gain of 25.1 per
cent in favor of the use of the former. The experiment proves that
the assumption that the use of American seed in growing seedlings
tends to increase the development of crown-gall is erroneous and it
indicates a superiority in seedlings from American seed.

The use of seedlings from old nursery districts for making root grafts
may not increase the development of the disease.—It has been asserted
by some growers of nursery stock that seedlings purchased from
regions where they had been grown year after year, and especially
from Kansas, developed more crown-gall than those grown in new
regions in soil where nursery stock had not been previously grown.
To test the matter, two lots of grafts were made from the same stock
of scions, including the following varieties: Yellow Transparent,
Baldwin, Winesap, Maiden Blush, and Missouri. One set was made
on seedling roots grown from French apple seed in the Kansas River
valley, near Topeka, Kans., on soil subject to inundation from the
river and overflow from neighboring nurseries and on which nursery
stock had been previously grown; the other set was from another
stock of seedlings grown from the same stock of seed by the same
nursery company in a new locality near Lincoln, Nebr., on soil which
had been cultivated in field crops for a number of years and on which
nursery stock had never been grown. This set contained half as
many root grafts.as the former. The grafts were made, planted,

and grown with the same care as in all of the experiments. They

were grown on cooperative plats 1 to 8, and a definite proportion,
selected in a numerical series in each row, was dug each year at the

ages of 1, 2, and 3 years. Table XI, in the appendix, gives in a

condensed form the results of the experiment.

In giving the results of this experiment it must be noted that the
conditions under which the seedlings for the experiment were grown
were not quite comparable for two reasons: The localities where they
were grown (Kansas and Nebraska) varied in latitude, and the soil
conditions were not quite the same, since these seedlings were grown

186

28 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE:

in different valleys. The trees from the two sets of grafts made from
these seedlings, however, were grown under similar conditions, and
the results of the experiment are of value, since they show what
variation may be expected from seedlings grown in different locali-
ties and since they disprove the prevalent idea that Kansas seedlings
are more apt to develop crown-gall than others. The results show
a decrease of 3.4 per cent in crown-gall and of 1.1 per cent in hairy-
root on trees from grafts on Kansas seedling roots. This is almost
entirely offset by the increased stand of trees, 3.1 per cent, obtained
from the trees grown from grafts on Nebraska seedling roots. The
experiment, then, yields no positive proof of an increase of the dis-
ease where seedlings are purchased from localities where nursery
stock has been grown for years.

Heavy wet soils favor the development of crown-gall in the nursery.—
The consensus of opinion of nurserymen, based upon observation, has
been that heavy wet soils underlaid with or composed largely of clay
favor the development of crown-gall. No extensive set of experi-
ments on this subject has been recorded. The most extensive experi-
ment recorded in scientific publications is that of Howard regarding
the increase of crown-gall due to clayey soil as compared with loess.

A large number of experiments have been conducted by the writer
on different kinds of soils, only two sets of which were conducted
in the same locality. These were on cooperative plats 1 and 2.
Plat 1 consisted of a low wet tract of land, composed of a colluvial
clay loam laid to a depth of 3 to 4 feet on a stratum of yellow clay.
Plat 2 was an upland, well-drained, light clay loam of about equal
depth, sloping gently to the south. The two plats were planted with
an equal number of root grafts made from healthy stock and prepared
in equal lots from twenty-four varieties of apples. The names of these
varieties are given on page 85. One-third of the trees, selected in a
numerical series, were dug each year for three successive years, at
the ages of 1, 2, and 3 years. The results are given in Table XII, in
the appendix.

Nearly the same amount of disease occurred in the two plats, 24.9
per cent in plat 1 and 24.1 in plat 2. There was a preponderance of
5.3 per cent of crown-gall on the heavier, wetter soil, and 4.5 per cent
of hairy-root on the higher, drier soil. Without regard to the cause
of the different forms of the disease, the usual rule with regard to the
increased production of roots in drier soils holds good in these experi-
ments. The well-drained upland soil in plat 2 yielded 20.2 per cent
more good trees than the other plat. These, however, were at least
a third smaller in size.

Six other cooperative plats, 3 to 8, were planted with experiments
identical with those in plats 1 and 2, since the root grafts for each

186

DEVELOPMENT OF FORMS OF THE DISEASE. 29

experiment in these plats were all made at one time in the same
nursery, divided into eight equal lots, and planted in each of the
plats. The location of each plat and a description of the soil are
given on page 78. It was noted that more diseased trees occurred
on the plats with the wettest, heaviest soils. The results from the two
plats with the heavier, wetter soils and from the two plats with the
lighter, better-drained soils are given in Table XIII, in the appendix.

The wet, heavy soils gave from 8.1 to 11.1 per cent more diseased
trees than the light, dry soils. The highest percentage of disease in
a number of smaller experiments has invariably occurred on wet,
heavy soils. It therefore appears that such soils are more favorable
to the development of crown-gall.

Period for the maximum development. of crown-gall and hairy-root umn
the nursery.—After compiling the data from a large number of experi-
ments, involving many trees dug at different ages, certain regular
variations were noted in the amount of crown-gall present at different
ages on root-grafted trees in the nursery aiden the Goud manus of
experimentation.

The results which follow are compiled from seven large sets of
parallel experiments carried on in four of the cooperative plats—
1, 2, 3, and 4 (see p. 78). The root grafts for each set were made
from carefully selected healthy stocks of scions and seedlings at the
same nursery, divided into four equal parts and planted in the four
cooperative plats just named. Twenty-four varieties of apples were
used, the same as are given in Table X XI, page 85, in the appendix.
One-third of the trees in each plat, selected in a numerical series in
each row, were dug each year, at the ages of 1, 2, and 3 years. The
results are given in Table XIV, in the appendix.

The results in Table XIV indicate plainly that in the nursery and
under the conditions given root-grafted trees developed crown-gall
chiefly during the first year, and that during the next two years many
of the trees threw off the disease, which decreased the second year
from 26.7 per cent to 9.1 per cent, and the third year from 9.1 to 4.7
per cent. This table also shows that the development of hairy-root
took place chiefly during the first year, but increased considerably
the second year, 3.1 per cent, with little increase the third year, 0.1
per cent.

An objection to making such conclusions from average results may
be offered for the reason that the average may be that of two widely
differing extremes, either of which might include the results of a
large number of the experiments, and that such extremes if taken
separately would warrant the formation of entirely opposite conclu-
sions. This objection can not hold here, since all of the sets of experi-
ments gave approximately the same general results as the average,

186 :

30 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE. ~

and even the smaller units or variations combined in these sets, with
very few exceptions, gave the same results. None of these excep-
tions varied widely from the general trend of the results. <A refer-
ence to the tabular results of a number of other experiments given
both earlier and later in this bulletin will lead to the same conclusions
as are drawn from Table XIV.

EFFECT OF THE DISEASE UPON APPLE TREES.
OBSERVATIONS BY OTHERS ON CROWN-GALL.

It has generally been held by pathologists that crown-gall is very
destructive to trees. Frank (14), in discussing the Wurzelkropf on
apple trees in Germany, notes that trees with very large galls show
a weaker growth of the trunk and branches, probably due to the fact
that the swellings absorb considerable nutritive substance. Wickson
(77), in discussing the general subject of root knots on fruit trees,
makes the following statement:

Probably during the last twenty years hundreds of thousands of such trees (referring
to trees with galls) have split and died in the best soil and with the best treatment.
If disease has stunted the growth of a young tree, pluck it out and plant a new one.
If the knots are found on larger trees which are making satisfactory growth in spite
of them, remedial measures should be tried. The final result seems to depend upon
whether the natural or the diseased growth secures ascendancy early in the life of the
tree; but apricot trees have been taken up after thirty years of satisfactory growth
and bearing and found to have roots badly affected with the knots.

In the same bulletin Woodworth makes this statement:

The presence of a gall at the crown of the plant seems to effect an obstruction to
the flow of the sap, and in this way a tree or vine becomes weakened and finally dies.
The gall generally attacks small plants, but not always, and it often takes a number of
years before the plant is killed.

Yates (80), in speaking of the crown-gall, does not consider the
same a disease.

Selby (50), referring to apple crown-gall, says: ‘‘It seems unlikely
that such affected trees will be worth planting, and all of them suffer-
ing with this trouble should be burned.”

Stewart, Rolfs, and Hall (64), make the following statement: **We
find crown-gall not uncommon on apple trees in the nurseries in
western New York, but we know of no case where it has caused
material loss. * * * Wewould recommend that all trees showing
the least trace of the disease be rejected; for, although we have never
seen any ill effects from the planting of affected apple trees, it appears
probable that the disease may thus be spread.’’ They refer to a
nurseryman who writes that he planted a row of healthy apple trees
and at the same time a row of trees affected with crown-gall, and
who states that after two years the trees with the crown-gall had made

just as good a growth as the healthy trees near by.
186

KFFECT OF THE DISEASE ON APPLE TREES. Bul

Garman (16), expresses an opinion to the effect that crown-gall
trees can never be very profitable, since in their enfeebled condition
they will not bear well.

Alwood (2), who made an extensive study of this disease, in his
introduction, referring to the results of his experiments, states that
these results ‘“‘seem to point clearly to the conclusion that every
planter must be prepared to detect this trouble, and exclude it from
his orchard plantings.”’ Commenting further on the results of his
experiments, Alwood says: ‘‘Our observations in more recently
planted orchards show that it is not usual for trees showing an attack
of this trouble to form a normal root system; the root development
is weak and confined to the surface. * * * We are also of the
opinion that badly diseased trees, such as are now very commonly
found in nursery stock, will not ordinarily come into fruiting.” In
a lecture before the Maryland State Horticultural Society Alwood (4)
is quoted as saying, in speaking of orchard trees diseased with crown-
gall, that ‘‘they have scarcely grown at all, although they have been
cultivated for five years.”

Butz (7), in speaking of eleven apple trees planted on the Pennsyl-
vania Agricultural Experiment Station grounds, reports that after
two years’ growth the trees showed “‘immediate injury, due to the
galls.’

Norton (34) states that ‘‘trees affected with crown-gall set out in
the college yard have never done well.” In a later publication (37)
he makes the following statements:

The galls, when they occur on the main root, may interfere with the transfer of the
sap in the tree, and thus weaken it. The constriction by the gall may cause the tree
to fruit too young, or to overbear; they cause abnormal root development, and thus
hinder the growth. They are often so well developed as to cut off and cause the
death of the taproot, which is almost always killed when affected throughout by the
hairy-root condition. The tissue of the gall may decay and form an entrance for
wood-rotting fungi which will soon destroy the tree.

R. E. Smith (55) reports apple crown-gall to be very common in
nurseries, but apparently it ‘‘does not result as seriously in orchard
trees as with the similar disease on stone fruits.”

Morris (33) makes the following assertion: ‘‘The trees affected
with galls at the crown are doomed to death sooner or later. Some-
times the trees are completely girdled and starved to death, at other
times the root of the tree is so weakened that it is easily broken by
wind.”’

Sandsten (48), concerning crown-gall, says:

Some kinds of fruit trees are less resistant than others. For example, it is well
known that a young peach tree infested with the disease will live for a relatively short

time, while apple trees may live for a number of years * * *. Perhaps the chiet
reason why fruit growers fear the disease is that just about the time when the trees

186 .

32 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

become profitable, or when the trees have attained the age of 8 or 10 years, they begin
to rot off at the crown and die. This is especially true of apples. I have particularly
in mind a thriving orchard in the Southeast of 25 acres of apple trees, 11 years old,
which bore a few crops, then all at once about half of them began to fall. Upon
examination it was found that the trees had been killed by crown-gall.

Van Deman (70), in a discussion on fungous diseases, is quoted as
follows, in a Virginia Horticultural Society Report, in answer to a
question concerning an apple tree diseased with crown-gall: ‘‘ Yes, sir;
it lives right along until it begins to bear, and then it begins to dwindle,
and you wonder why. * * * It doesn’t attain the size of other
trees, though sometimes it is fairly vigorous. The gall will, however,
keep on growing for years and years.”

Popenoe (44) reports the following Snes: A lot of Ben Davis
trees, 2 years old, one half having visible galls on the roots and the
other half being similar trees without galls, were planted a few years
ago on rich, second-bottom, level, black land on the station grounds
at Manhattan. At the time the report was made, in 1903, Popenoe
says: ‘‘There is practically no difference in the growth above ground
of the trees of the two lots, and of the trees originally clean of galls,
ome are now affected.’

OBSERVATIONS BY OTHERS ON HAIRY-ROOT.

In the various citations as to the effect of crown-gall on trees there
is little or no reference to hairy-root. Stewart, Rolfs, and Hall (64),
referring to the hairy-root of seedlings, which we have designated as
the simple type, state that ‘‘affected trees are worthless for planting.”

Garman (16), discussing a knot disease of apple trees which is evi-
dently the aerial form of hairy-root of the woolly-knot type, makes
the following statement:

It undoubtedly weakens the trees attacked, but does not keep them from bearing
in all cases, and when but few knots are present the trees show no other outward
evidence of disease.

In a letter dated September, 1907, Garman writes as follows con-
cerning the disease: ‘I am satisfied it is not spreading, and I do not
regard it as particularly destructive, although I have no doubt it
affects the health of the tree when a great many of the knotty growths
are present.”

The gist of the foregoing quotations, which include a summary of
nearly everything that has been published on the effects of crown-
gall and hairy-root in this country, is that in the opinion of a majority
of those observers who have investigated these forms of disease, they
are to be considered dangerous and likely to weaken or kill affected
trees. This general opinion concerning the nature and effect of
crown-gall of apple trees seems to have gained ground largely as a

186

EFFECT OF THE DISEASE ON APPLE TREES. 30

result of the opinion expressed by Toumey (68) concerning crown-
gall of the almond, who proved that it may be highly contagious and
extremely destructive.

Beginning with the date of Toumey’s paper on crown-gall of the
almond, without waiting for further proof, the general assumption
has been that the effect of crown-gall upon the apple tree is identical
with that of this disease upon the almond. With the general opinion
prevalent in most parts of the country, vigorous methods have been
advocated very generally by pathologists, entomologists, nursery
inspectors, and others. Stringent laws have been enacted for stamp-
ing out the disease, with the assumption that the disease of the apple
is as injurious as that of the stone fruits.

In summing up the few opinions which were given from actual
experiments, it may be well to suggest that in all probability the
effect of root-rot has been confused with that of crown-gall. It is
well known that root-rot attacks orchards in many portions of the
apple-growing belt, especially in the South and the Southwest. In
collecting accurate data on the effect of crown-gall and hairy-root it
is absolutely necessary that each individual tree be examined and
the condition of the roots noted before drawing any conclusions as
to the cause of the death. A study of the connection between root-
rot and crown-gall is also necessary. Al! of the trees in the orchard
experiments of the writer have been free from root-rot, but borers
were present in orchards 1 and 2 and killed all of the trees that died
after the first year, but attacked healthy and diseased trees alike. In
forming conclusions as to the cause of the death of an apple tree, not
only root-rot but also these borers should be taken into account,
since they apparently attack smooth-rooted trees as often as those
diseased with crown-gall and hairy-root. These insects bore beneath
the bark into the wood of the tree and allow root-rot fungi to enter
the wounds made by them. Quite often death results in a couple of
years from the first attack.

Wherever an orchard has been reported as dying in a short time
from crown-gall it will be well to look deeply into the causes of the
death of the trees before accepting the report as a scientific fact. In
the writer’s opinion, which is based upon exact orchard experiments,
crown-gall never kills an apple tree suddenly, and where no other dis-
turbing factor enters, it may not be able to kill it at all. The wound-
ing of a projecting hard or soft gall may enable wood-rotting organ-
isms to enter the tree and kill it. Again, the presence of gall tissues
may the better enable insects to attack the tree, but in the writer’s
experiments he found no proof that diseased trees were more subject
than healthy trees to the attacks of insects and wood-rotting fungi.

50414°—Bul. 186—10——3

34 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

EXPERIMENTS ON THE EFFECT OF THE DISEASE ON APPLE TREES.
EFFECT ON SEEDLINGS NOT UNIFORM. |

No extended experiments have been made to determine the effect
of crown-gall and hairy-root on seedlings. From small experiments
and from observation the following conclusions have been reached:
On yearling seedlings with relatively large galls encircling the root
(Pl. II, fig. 2) or with a very abundant formation of fine side roots
(Pl. IIT, fig. 1), such as accompany extreme forms of hairy-root, there
is a perceptible stunting of the growth of the tree. Where the galls
are small and the hairy-root formation is not extensive, no apparent
effect on the growth is noted. In the latter case, as the trees grow
older, they may outgrow the effects of the disease.

The aerial form of hairy-root (stem tumors) was found in the
autumn of 1908 on 40 trees in a block of 500 8-year-old seedling apple
trees in a pedigree orchard near Mitchell, Ind., belonging to the Indiana
Agricultural Experiment Station. These were first reported in a
letter by Prof. C. G. Woodbury, of that station. Six of these trees
bore from 8 to 25 large, rough knots (Pl. V, fig. 1), in some cases
encircling the tree. None of these trees was quite as large as the
neighboring trees. No difference in size was noted in the other 34
diseased trees.

One striking effect of hairy-root of the simple form should again
be noted. Seedlings diseased with this form are enabled to root
more readily than healthy seedlings. Cuttings taken from such
seedlings root more readily than those from healthy seedlings (see
p. 24). Such cuttings usually develop into trees (Pl. VII, fig. 1),
affording to some extent a method of propagation not ordinarily
used and not to be recommended.

SLIGHT EFFECT ON GRAFTED TREES IN THE NURSERY.

The same observations made on the effect of crown-gall and hairy-
root on seedling trees apply to young grafted trees, except that the
stunting, as a rule, is not nearly so marked. A great variation in
effect is shown, since some diseased trees exhibit as great or even a
greater vigor of growth than healthy ones. On the average, how-
ever, trees in the nursery rows that are diseased with the simple
form of hairy-root are not quite so tall as smooth-rooted trees, and
those with the woolly-knot form may be taller. Those affected with
forms of crown-gall are somewhat shorter than those with hairy-root.

In order to determine the effect of the disease on the height of
trees in the nursery rows, measurements were taken of 18,042 1 and
2 year old root-grafted trees grown in a number of the experiments

mentioned earlier in this bulletin. These trees were grown in coop-
186

bers

EFFECT OF THE DISEASE ON APPLE TREES. 35

erative plats 1 and 2, in southwestern Iowa; plat 3, in eastern
Nebraska; plat 4, in western Illinois; and plat 6, in eastern Kansas.
In five of these sets of experiments, the results of which are given in
Tables XV and XVI, in the appendix, a definite proportion of the
trees, selected in a numerical series in the row, was dug at the age of
1 year, and the remainder at the end of the following season.

From Tables XV and XVI it will be seen that the average height of
healthy trees in the experiments at the age of 1 and 2 years was 37.2
and 56.4 inches, respectively, as compared with 33.5 and 51.3 inches
for trees diseased with crown-gall and 34 and 53 inches for trees
affected with hairy-root. In other words, galled trees were only
ninety hundredths and ninety-one hundredths and hairy-rooted trees
ninety-one hundredths and ninety-four hundredths as tall as healthy
ones. A few measurements of root-grafted trees made at the end of
three years indicate that approximately the same rate for each still

held at the end of the third year’s growth. A few measurements

were made of the diameter of healthy and diseased trees of some of
the rows in each experiment, but time would not permit of the meas-
urement of all. It was found that the ratio of the diameters was
approximately the same as that of the heights, viz, almost 10 to 9.5
for healthy and diseased root-grafted trees in the nursery.

In conclusion it must be said that taken collectively the forms of
crown-gall and of hairy-root do have a slightly stunting effect on
root-grafted trees in the nursery during the first three years, and for
that reason, at least, such trees are not equal to healthy ones for plant-
ing in orchards. This conclusion as to hairy-root is given with the
following modifying statements:

(1) The effect of the simple form of hairy-root in stimulating root
production in root grafts is described on a previous page. When
cuttings are taken from trees diseased with the knots or the aerial
form of hairy-root and planted or used as scions, root formation is
more abundant than with healthy cuttings. Roots are thrown out
readily, especially from the young knots, producing the woolly-knot
form (PI. V, fig. 2, and Pl. VII, figs. 1 and 2). Such trees are some-
times more vigorous growers for a time than healthy trees. The final
effect is not yet known.

(2) The abnormal root production of the woolly-knot form often
stimulates the growth of grafted trees, and, as a result, such trees fre-
quently become the largest in the row. This stimulation often con-
tinues after the trees are planted in the orchard. The largest tree in
experimental orchard 1 was diseased with woolly-knot (PI. IX, fig. 1). °

LITTLE OR NO EFFECT ON ORCHARD TREES SHOWN IN EXPERIMENTS.

Experiments by others—Orchardists and nurserymen, as well as
investigators, differ in their opinions as to the effect of crown-gall and
186

36 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

hairy-root on the apple tree. It would be interesting to cite the
statements of a number of nurserymen and orchardists, but it will be
better to give data from orchards grown by them with diseased trees.

The owners of one orchard, Marshall Brothers, at Arlington, Nebr.,
reported in a letter dated January 25, 1909, as follows:

We have 29 Wealthy apple trees that we planted thirteen years ago. All of them
were more or less galled, some galls being nearly as large as a hen’s egg. These trees
have grown well and have done splendidly. We have noticed no difference between
these and other Wealthy trees of the same age in growth and bearing. They have
given almost annual crops the last five or six years, and two or three very heavy crops.

The owners of a second orchard, of 10 acres, at Troy, Ohio, reported
May 16, 1907, as follows:

The orchard you ask about was planted five years ago this spring and consisted of
Yellow Transparent apples which were badly infested with crown-gall and aphis.
Inasmuch as the authorities in this State are opposed to the use of trees thus infested,
we have discontinued the growing oi apples at this place, and therefore did away with
the orchard this spring. However, we wish to say the trees were thrifty and in good
growing condition, and we do not believe there could be any objection to the showing
they made. There was some fruit on this orchard last season.

A third orchard is reported upon by Charles C. Bell, of Boonville,
Mo., January 4, 1908. He states that an orchard of about 20 acres
was planted in 1900 with 2-year-old trees diseased with crown-gall,
after samples of the trees had been condemned by experts, as unfit for
planting. He says: ‘‘To-day these trees which were condemned
* * * are a beauty’to behold; they are healthy and strong and
ready to bear fruit.”

A fourth orchard was planted and grown in 1902 near Mountain
Grove, Mo., by F. A. Faurot, a collaborator of the Bureau of Plant
Industry. This experiment was in cooperation with the Missouri
Fruit Experiment Station at that place. By permission of the di-
rector of the station, Paul Evans, Mr. Faurot furnished the data for
publication. The orchard is planted in two plats, one sloping gently
to the east, the other to the north. The soilisaclayloam. In the
first plat 275 apple trees were planted, one-fifth of which were diseased
with crown-gall. The diseased trees were in a separate row, but were
of the same varieties and of the same stock as the healthy ones. The
second plat consisted of 96 apple trees, one-third of which were
plainly diseased with crown-gall. In company with Mr. Faurot, the
writer visited the orchard in the autumn of 1908. No difference could
be detected in the growth and appearance of the trees in the diseased
rows of trees when compared with those in the healthy ones. Rela-
tively, in number, no greater proportion of the diseased trees had
died in six years of growth. No evidences of premature development,
such as early bearing, stunted growth, etc., were noticed in any of the
diseased trees.

186

EFFECT OF THE DISEASE ON APPLE TREES, Syl

A fifth orchard, belonging to the Arkansas Agricultural Experiment
Station, located at Fayetteville, Ark., has been under the observation
of the writer for five years. This orchard is 15- years old and was
planted as an experiment to test varieties of apples from a horticul-
tural standpoint. Twelve out of a hundred trees in this orchard,
mostly Russian varieties, have developed the aerial form of hairy-
root, with no apparent effect as yet upon the growth or the fruiting
of the trees.

A sixth diseased orchard is situated near Mitchell, Ind., on the farm
of the Burton Fruit Company. Among other older trees there are
planted over two hundred Benoni apple trees now 8 years old. This
orchard was visited by the writer in the autumn of 1908. More than
half of the Benoni trees are diseased with the aerial form of hairy-root,
with little or no apparent effect, as yet, on their growth. Mr. Joseph
A. Burton, superintendent of the orchard, asserts that many of the
knots disappear as the trees grow older, but that their immediate
effect is to make the trees bear younger. In an older orchard belong-
ing to Mr. Burton there is a thrifty 25-year-old Chenango apple tree
that has been diseased with the aerial form of hairy-root for years,
with no effect upon its fruitfulness.

In summing up the data from these orchards, the results show
that crown-gall and hairy-root have but little immediate effect on
the growth of trees in the orchard. Orchards that were reported
dying from disease have been examined by the writer, but the immedi-
ate causes on examination have proved to be heart-rot and root-rot,
usually accompanied in unfavorable soil conditions by poor drainage,
neglect of cultivation, etc. These diseases apparently attack and
kill the trees originally healthy, without regard to the presence of
crown-gall or hairy-root.

Experimental orchards—The orchard experiments conducted for
the study of the disease were four in number. ‘The location of these
orchards, designated as orchards 1, 2, 3, and 4, and a description of
the soil in each, with the methods of experimentation, are given on
page 79.

Orchard 1 was planted with trees of the following varieties: In-
gram, Gano, Collins, and York Imperial, grown in a nursery in
eastern Missouri. It was planted with 112 healthy apple trees
(Pl. III, fig. 3) and 96 diseased with the hard form of crown-gall, the
galls being near the crowns of the trees, just below the surface of the
soil as they grew in the nursery (PI. I, fig. 1). This orchard was on
well-drained soil, and the healthy and diseased trees were planted
in alternate rows.

Orchard 2 was planted in a soil similar to that of orchard 1, except
that it was situated at a lower elevation and was subject to seepage.

186

38 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

It was planted with the same varieties, but the healthy trees, 122
in number, were planted in blocks of several rows, rows of healthy
trees alternating with rows consisting of 139 diseased trees. Both
orchards were cultivated across rows, from diseased to healthy trees,
to facilitate the spread of disease by cultivation. One block of 36
diseased trees of the Collins variety in this orchard was composed of
trees diseased with the soft form of crown-gall, the other varieties
being diseased with the hard form. Most of the galls were from 14
to 2 inches in diameter.

Orchards 1 and 2 were cultivated with ordinary care, receiving
no special attention. The trees were planted thickly and stood 8
by 9 feet apart. The soil was not the best, owing to the fact
that it had been cultivated to grain crops without fertilization for
many years. No fertilizer was used, natural soil conditions being
preferred. The growth of the healthy and the diseased rows was so
nearly uniform that on repeated tests trained pathologists could
not pick out the rows of diseased trees. Photographs of represen-
tative rows of trees were taken at the age of 6 years (see Pl. X).

Owing to a fire which killed many of the trees in orchards 1 and rl
the experiments had to be discontinued, and the trees were taken up
when they were 8 years old; that is, after they had grown for six
seasons in the orchards. Just before the trees were taken out, the
trunk of each was carefully measured at a height of 6 inches above
the surface of the ground. At the time of removal careful notes
were taken of the condition of the roots as to increase of disease,
recovery therefrom, forms of disease, etc. The results of the experi-
ment are given in a condensed form on pages 20 and 57 and in Tables
XVII, XVIII, and XIX, in the appendix. Table XVII gives the
average diameter of the healthy and the diseased trees at the time
they were dug.

Tt will be seen from Table XVII that the effect of crown-gall and
hairy-root on the trees in the experiment was to diminish Very slightly
the diameter of the trunks. The trees with healthy roots had
developed in six years an increase in diameter of six one-hundredths
of an inch greater than those diseased with hairy-root, and of twenty-
nine one-hundredths of an inch greater than those diseased with
crown-gall. These diseases are thus shown to be very slightly
detrimental to the growth of orchard trees during the first few years,
and the assertions of many to the contrary are disproved.

In orchards 1 and 2, during the six seasons of growth the number
of healthy trees that died was 23 out of 234, or 9.8 per cent, and of
diseased trees 1t was 30 out of 235, or 12.8 per cent, indicating that
the presence of the disease may have slightly increased the death
rate. During the first four years 9 healthy and 9 diseased trees died.

186

EFFECT OF THE DISEASE ON APPLE TREES. 39

Of these 5 healthy and 7 diseased ones died from the effect of trans-
planting to the orchard. During the fifth year 10 healthy and 12
diseased trees died, and during the sixth year 4 healthy and 9 dis-
eased trees died. It should be noted, however, that all of the trees
that died during the fifth and sixth years and 3 trees during the
first four years were killed by borers encircling the trunk near the
surface of the ground. In no case could their death be directly
attributed to crown-gall or hairy-root, nor can it be said that borers
prefer the diseased trees to any marked extent.

Tables XVIII and XIX, in the appendix, show the number of
healthy and diseased trees of each variety planted in orchards 1 and 2,
as well as the number of each that died during six seasons of growth.
The diseased trees of the variety Collins in orchard 2 had soft galls
on the roots. All of the other galls were of the hard form. —

A third orchard, designated as ‘‘orchard 3,’ was planted in the
latter part of April, 1907, with 1,108 well-rooted apple trees of a num-
ber of varieties selected from trees grown in experiments in the
nursery. Of these 572 were healthy, 354 diseased with hairy-root
(Pl. I, fig. 2), and 117 diseased with crown-gall of both the hard and
the soft forms. The trees were transplanted after the buds were
greatly swollen, and a month of dry weather ensued just after the
planting. As a result, the loss from transplanting was heavy. A
fire in the autumn of 1908 killed many of the trees and ruined the
experiment. The trees were then dug, no notes being taken at the
time of digging as to the condition of the roots. The trees that died
in 1907 and 1908 are enumerated in Table XX, in the appendix.

By combining the data for 1907 and 1908 in Table XX, it is found
that in two years 33.4 per cent of the healthy trees died, and at the
same time 37.3 per cent of those diseased with crown-gall and 25.1
per cent of those diseased with hairy-root. Again it must be said
that the reason for the increased vitality of the trees diseased with
hairy-root is the greater tendency to throw out roots. This has
already been mentioned in the case of seedlings affected with hairy-
foot (see pp. 24 and 34). On the other hand, the trees diseased with
crown-gall had slightly less vitality, since a somewhat greater number
died.

A fourth experimental orchard, partly described on page 79, was
planted on the Potomac Flats, near Washington, D. C., in 1907 and
transplanted to the experimental farm at Arlington, Va., m 1908.
Trees of the following varieties, grown in a nursery in eastern Mis-
souri, were planted: Jonathan, Grimes, and Gano. The trees dis-
eased with crown-gall and hairy-root were selected on account of their
having intense forms of disease, in addition to possessing as abundant
roots as the healthy trees. During the two years that have elapsed

186

40 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

since planting only 8 trees have died, in spite of the fact that the trees
have been twice transplanted. Out of 225 healthy trees, 3 have died;
of 82 trees diseased with hairy-root, 2 have died; and of 193 trees
diseased with crown-gall, 3 have died, the percentage being but
slightly in favor of the healthy trees. This difference is so small as
to depend entirely on chance.

The experiments mentioned, as well as observations made in other
orchards, indicate that the mere presence of the forms of crown-gall
or of hairy-root at or near the crown of an apple tree, in the orchard
has very little effect on the subsequent growth of the tree, provided it
has a well-developed root system.

Observations made on badly diseased trees growing elsewhere
under poor soil conditions indicate that where either hard or soft galls
extend entirely around the main root of a tree, unless it is able to
throw out roots above such growths, a marked stunting effect may
follow. A grafted tree of this character can not develop into a good
tree unless it can form roots on the scion portion above the union.

It is inadvisable on general principles to plant any trees affected by
a contagious disease like crown-gall, and particularly so with varie-
ties that do not root well from the scion. Trees of the following
varieties are more likely to overcome a mild attack of crown-gall, as
they are better able to root from the scion: Ben Davis, Wolf River,
Northern Spy, Grimes, Gano, Northwestern Greening, Missouri,
Wealthy, Walbridge, Fameuse, and Salome.

The following statement made by Wickson (77) fully meets the
views of the writer and applies to hairy-root as well as to crown-gall:

If the diseased growth is so extensive during the early period of the life of the tree
as to stunt the development of the root system, no favorable results can be expected
during the later period of development of such a tree. It is fortunate that nursery
trees are generally dug and sold at a period when the stunting effect of these diseases
is most marked.

The same statement might be made of many poorly rooted trees
which have not formed a perfect union between scion and root piece
in the root graft and as a result have a defective root system, irrespec-
tive of these diseases. These constitute a considerable loss to the
- nurseryman where poorly fitted root grafts are used.

These statements apply to both hard and soft crown-gall and to all
of the forms of hairy-root found in the nursery. The results of the
investigation indicate very clearly that apple trees are able to resist
the effects of these forms of disease in the orchard, and their impor-
tance has been greatly overrated.

It must not be understood, however, that trees diseased with even
the milder forms of crown-gall and hairy-root are fully as valuable
for planting as healthy trees. They can certainly not be rated as

186

- SUSCEPTIBILITY OF VARIETIES OF APPLE TREES. 4]

first grade in the markets, and if a purchaser buys trees guaranteed
to be free from disease and of first grade, trees with distinct forms of
disease should not be supplied. Orchardists should plant healthy
trees and be willing to pay more for them if necessary. Since the
initial cost of an orchard is only a small item in the entire outlay for
its maintenance, it will certainly pay to plant the best grade of trees
that can be bought.

SUSCEPTIBILITY OF VARIETIES OF APPLE TREES TO THE DISEASE.
DATA UPON A NUMBER OF COMMON VARIETIES USED IN EXPERIMENTS.

The susceptibility of the different varieties of apple trees to crown-
gall and hairy-root has not been discussed by others in any previous
publication on the subject. Nurserymen have asserted for a number
of years that certain varieties are extremely susceptible to the disease.
Since the same varieties are not grown in all localities, sometimes one
variety has been named as more susceptible and sometimes others.
A request for a list of the varieties considered to be ordinarily most
badly diseased with crown-gall and hairy-root was sent to fifty of the
leading nurseries in various parts of the country to ascertain if there
was any uniformity of opinion in this matter. . Each was requested
to have the field superintendent send in the names of the six worst
diseased varieties. In a compilation of thirty-two replies the follow-
ing varieties were found to be the most badly diseased, those named
oftenest being given first: Ben Davis, Early Harvest, Yellow Trans-
parent, Wealthy, Grimes, Oldenburg, Wolf River, Red June, Gano,
and Rome Beauty. All of these varieties except the last named have
been included in the experiments of the Bureau of Plant Industry,
from which data will be given later.

Since obtaining these opinions reports have been received for three
successive years from twelve nurseries, the number of diseased trees
being given in the case of a large number of varieties. The reports
are from nurseries in Utah, lowa, Nebraska, Kansas, North Carolina,
Missouri, Illinois, Indiana, Ohio, and Virginia, and many of them were
based upon careful counts made at the time of digging. These cor-
roborate quite generally the opinions of the nursery superintendents
as given in the preceding paragraph. They show, however, as would
be expected, a variation year by year with the same varieties in the
same locality. For instance, one nursery reports for the Gano the
following percentage of disease during successive years: 1904, 15;
1905, 46; 1906, 28. Another reports as follows for the Ben Davis:
1904, 15; 1905, 40; 1906, 30.

In order to obtain some idea as to whether in certain varieties there
was a susceptibility to either crown-gall or hairy-root, or both, experi-

186

——

tet SE

| a

49 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

ments with twenty-four of the more valuable commercial varieties of
apple trees were conducted in connection with the other lines of inves-
tigation. The data from the trees that were grown in these experi-
ments from ordmary whip grafts have been carefully recorded and
compiled for five years. <A larger number of grafts were planted and
dug during the last three years than during the first two of the period
of experimentation. During the first two years, 1903 and 1904, the
work of experimentation was confined to one locality. During the
last three years each stock of root grafts was made at a single nursery
and divided into eight equal lots and planted in cooperative plats 1
to 8, thus getting the combined results of the effect of growing a
variety under as many different conditions. The results from these
series of experiments for five years are combined and given in Table
XXI, in the appendix.

The conclusion from this series of experiments is that the different
varieties of apple trees show a wide variability in their susceptibility
to the disease; that some varieties are more apt to develop forms of
crown-gall and others forms of hairy-root; and that none of the varie-
ties were free from either type of the disease.

It will be noted that the varieties Wealthy, Yellow Transparent, and
Wolf River developed a high percentage of crown-gall, and the Ben
Davis, Wolf River, and Northern Spy varieties a high percentage of
hairy-root. In both cases the forms of disease occurred chiefly on the
scion portions of the trees. (See Pl. I1,fig.3.) It follows that the dis-
ease must be considered more with reference to the scion than to the
seedling or root portions of the root graft; also that m root-grafted
trees, susceptibility or resistance is inherent in the variety of scion,
and methods for the prevention of the disease must be directed
primarily to the selection of varieties resistant to the disease, and
secondarily to the selection of resistant seedling stocks.

The tendency toward the development of the disease appears to be
in no way related to the character of the growth of any particular
variety. Certain of the varieties experimented with are vigorous
growers, such as Wealthy, Walbridge, Wolf River, Minkler, Ben
Davis, Northwestern Greening, Northern Spy, and Baldwin, while
others, like Yellow Transparent, Whitney, Red June, Maiden Blush,
and Jonathan, are much slower growers. It will be seen from Table
XXYVI, in the appendix, that some of the more vigorous varieties
showed a high percentage of disease, as, for example, the Wolf River,
with an average of 46.4; the Wealthy, with 43.3 per cent; and the
Ben Davis, with 36.1 per cent. On the other hand, equally vigorous
growers were the Baldwin, with only 16.6 per cent; the Minkler, with
16.8 per cent; the Walbridge, with 14.1 per cent; and the Martha,
with only 10.7 per cent. It must be added, however, that there was

186

SUSCEPTIBILITY OF VARIETIES OF APPLE TREES. 43

a doubt as to whether the variety called ‘‘Martha”’ used in the experi-
ment was true to name. Of the slow-growing varieties, the Yellow
Transparent showed an average of 34 per cent of diseased trees, the
Maiden Blush 26.4 per cent, and the Whitney 20.4 per cent. It must
be concluded that susceptibility is not directly related to vigor of
erowth.

It was found that those varieties that throw out roots more readily
from the scion are the ones that are most susceptible to hairy-root.
The forms of hairy-root apparently originate only in tissue centers
capable of producing adventitious roots.

SUSCEPTIBILITY OF SCIONS GROWN IN DIFFERENT LOCALITIES.

The collection of data on the susceptibility of different varieties of
apple trees to crown-gall and hairy-root brought out the fact that
while certain varieties were found to be more susceptible than others,
the same variety during the same season or several seasons was dis-
eased more in one locality than in others. This could probably be due
to a number of facts, one of which might be a varying susceptibility
in stocks of the same variety grown in different localities.

To ascertain whether there was any difference in susceptibility of
stocks in different sections of the country, scions of three different
varieties of trees were obtained from a number of nurseries from Ohio
to California. These varieties were Wealthy, Wolf River, and Yellow
Transparent. Each variety was made into root grafts, the same stock
of seedlings being used. They were planted in 1906, each variety in
a different plat, and grown three years before digging. The names of
the nurseries furnishing the scions are not given, numbers being sub-
stituted, but the State in which each nursery is located is given.
Table XXII, in the appendix, gives the number of trees grown from
each lot and the percentage diseased.

From the results given in the table it will be seen that there was
a great variation in the amount of disease present in scions taken
from different localities, but it will not be safe to ascribe this wholly to
sreater susceptibility, since the health of the trees from which the
scions were selected in each locality could not be ascertained, and it
has already been shown that this is a factor in the problem.

The difference in the percentage of disease in the case of the Wolf
River variety, as shown by the two extremes in the results from the
experiment, is 14.7 percent. In the experiment with the Wealthy itis
17.5 per cent, and with the Yellow Transparent 12.8 per cent. This
is quite a wide range, but since the results can not be considered as
strictly comparative they may be taken as tentative, paving the way
for further inquiry along this line.

186

44 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE,

COMMUNICABILITY OF THE DISEASE IN THE NURSERY AND THE
ORCHARD.

PREVIOUS PUBLICATIONS ON THE COMMUNICABILITY OF APPLE
CROW N-GALL.

Ever since crown-gall and hairy-root have been brought to the
attention of plant pathologists one of the chief problems under dis-
cussion was related to the question of whether these forms of disease
are communicable, especially under nursery and orchard conditions.
As a matter of precaution, growers have been generally advised to
refrain from planting diseased trees, and their destruction, both in
the nursery and the orchard, has been recommended. In some cases
trees to the extent of a carload at a time have been condemned by
zealous nursery inspectors and destroyed on account of the presence
of diseased trees.?

The earlier accounts of the fae by W. E. Smith (56), Yates (80),
Bailey (5), and others, are based upon the idea that the disease is
probably not communicable, but later researches have overthrown
this theory.

Woodworth (78) recommends rejecting all affected stock, purchas-
ing from nurseries known to be entierely free from crown-gall, burn-
ing diseased trees, and devoting fields in which the galls have appeared
to some other crop for a number of years.

Toumey (68), in his work on the crown-gall of the almond, records
an experiment in which he attempted to transfer the disease from
the almond to the apple, both by soil inoculation and by graft inser-
tion, but was unable to communicate the disease. ?

Selby (52) recommends the destruction of all affected stock, and
Says:

Soil which causes this sort of growth upon peach trees in the nursery has been known
to produce the same upon the apple, and conversely.

Garman (15) makes the following statement, without citing proofs:

It has been demonstrated that crown-gall is a contagious disease, to be conveyed to
seedling trees by crushing the galls and putting them in soil in which seeds are planted.
Trees grown with others that are galled are therefore not above suspicion, even when
they show no outward evidence of the disease.

Guilford (17), speaking of apple crown-gall, says:

For the past three years I have been trying to inoculate the Virginia crab roots with
this gall. Conditions were made favorable by wounding the roots and covering them

a Paddock, Wendell. Crown-gall. Bulletin 86, Colorado Agricultural Experiment
Station, 1903, p. 5.

6 Dr. Erwin F. Smith has shown the writer large, hard crown-galls on apple stems
produced by him in 1908 by pure-culture inoculations of Bacterium tumefaciens
obtained from the soft crown-gall of the peach.

186

COMMUNICABILITY OF THE DISEASE. 45

with galls. I have failed to get a catch; but I have no trouble in making the inocu-
lation on our common seedlings. They usually take hold on the seedlings at the graft
union. F ;

This would seem to indicate immunity of the Virginia crab.

Howard (24) made a number of experiments to test the contagious
nature of different galls, using apple grafts, and found that apple
trees inoculated with apple galls were affected to the extent of 30
per cent; apple trees inoculated with raspberry galls, 162 per cent;
and apple trees inoculated with peach galls, 22 per cent. He, however,
gives no comparative results with apple trees which had not been
inoculated; hence, it is not certain that his results are due to inocu-
lation.

Alwood (2) states:

Apparently crown-gall can be readily inoculated from a diseased plant into healthy
ones; hence, diseased plants should not be allowed to remain among healthy ones in
the orchard.

In another publication Alwood says:

Cultivating the orchard may possibly serve to spread the disease by carrying disease
germs from one tree to another. It is very probable that infection occurs without
assistance wherever parts of the diseased tissues remain in the ground occupied by
apple trees.

Alwood bases his conclusions in the first instance upon experiments
containing a small number of trees.

Norton (37) regards crown-gall as a communicable disease on the
apple, and says that ‘‘in grafting, the disease may be communicated
from diseased to healthy trees by means of knives, etc.” He does
not, however, give experiments or cite authority for the statement.

Butz (7) states that healthy trees set in infected land develop the
disease within a year or more.

The author (19) stated in a bulletin in 1905, concerning the hard
form of crown-gall-on apple trees, that ‘‘the results of extensive inoc-
ulations with this type have failed to prove that this disease is of a
contagious nature.” And again, concerning the soft form of crown-
gall: “Nor is there proof yet that they are of a contagious nature.”
Similar statements were published in 1905 in Science (18) and in the
National Nurseryman (18). These opinions were based upon a
failure to secure positive results from inoculations of apple trees
with pieces of hard galls in earlier experiments, disease occurring
both in control and in inoculated plants.

Later experiments by the author (22) in 1906 and 1907 and pub-
lished in 1908 established the fact that crown-gall of the soft form
on apple trees was contagious and that it was identical with crown-
gall of the almond, apricot, blackberry, cherry, peach, plum, prune,
chestnut, and walnut. These experiments also indicated that the
disease in the hard form was either slightly or not at all contagious.

186

46 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

From the preceding citations, which are representative, it is appar-
ent that the opinions of plant pathologists, with few exceptions,
have been as follows:

(1) Apple crown-gall spreads rapidly in the nursery and the orchard
from tree to tree.

(2) It may be communicated from diseased to healthy trees by
contact, in bundles, etc.

A review of the literature on the subject reveals that little has been
done previously in the way of experimentation to substantiate these
views as to the degree and the rapidity of the spread of the disease
in the nursery and the orchard.

PREVIOUS PUBLICATIONS ON THE COMMUNICABILITY OF HAIRY-ROOT.

The previous citations bore upon the communicability of crown-
gali, but i most cases the statements made no separation of crown-
gall from hairy-root, both types of disease being included under the
term “ crown-gall.”’

Stewart, Rolfs, and Hall (64), who first described hairy-root of
the apple, did not express their opinion as to the communicability
of the disease, but regarded it as separate and distinct from crown-
gall.

EXPERIMENTS ON THE COMMUNICABILITY OF THE DISEASE.

Studies on the formation of callus as related to crown-gail.—In order
to study the relation of callus to wounds an experiment was prepared
with a number of sets of apple cuttings, seedlings, and root grafts.
Some of the cuttings were made with blunt or square ends, others
with slanting or pointed ends. Some were cut with longitudinal
incisions, some with spiral incisions, and some with cross incisions
through the bark and cambial layer; others lacked such incisions.
The seedlings were washed clean, sterilized for five minutes in a one-
tenth per cent water solution of corrosive sublimate, and again
washed in boiled water. They were cut off at both ends, roots and
shoots, to the length of 9 inches. The root grafts were made of the
tongue or whip-graft pattern, some closely fitted, some poorly fitted,
others with the upper end of the root cut off bluntly, and others with
the lower end of the scion cut off in the same manner.

The materials were prepared for the experiment the Ist of Febru-
ary, the usual time for root grafting at the larger nurseries in the
Mississippi Valley. The cuttings, seedlings, and root grafts of each
pattern were tied for storage in bundles in the same manner as root
grafts are tied for storage at nurseries. They were divided into two
equal series, one of which was stored in a cool cellar at a temperature

186

COMMUNICABILITY OF THE DISEASE. A7

of 50° to 60° F’. and the other in a greenhouse at a temperature of
65° to 90° F.

Both series were packed in sterilized jars in a number of different
kinds of packing. The jars and substances used in packing were
sterilized in an autoclave at a temperature of 239° F. for three hours.
The sets were placed under the following conditions of moisture in
the cellar and the greenhouse: (1) Moist sphagnum moss; (2) moist
sand; (3) moist sawdust; (4) moist soil; (5) moist chopped excelsior ;
(6) moist air over water, surrounded by wet blotting paper; (7) all
but the tips of the upper ends in water.

In nursery practice root grafts are made and either planted out
immediately or stored in moist conditions until the wounds are filled
with callus. Of the two sets of root grafts in the experiment those
placed under the cooler conditions formed callus about one-half as
rapidly as those in the warmer conditions. Those in the warmer -
conditions, had they been in the nursery, should either have been
planted at the end of ten to fourteen days or placed in cold storage
to inhibit further development of callus. Those in cooler conditions
were ready to plant in three to four weeks, and at the end of six
weeks the formation of callus had become excessive, especially in
moist moss, earth, sawdust, and chopped excelsior. Sand was found
to be much the best for packing root grafts, since only a moderate
formation of callus took place. In this substance there was no exces-
sive formation of callus except in a few cases when the period of time
in the cellar was extended to two months. The grafts, however, after
two months in the cellar or one month on the benches had begun to
form shoots and roots, and for this reason were not in good condition
for planting.

The experiment gave the following general results:

(1) On apple cuttings callus formed readily but not excessively in
spiral and cross incisions, and less readily in longitudinal incisions,
filling the cuts with new tissue, and in the former often projecting
from the surfaces in small outgrowths.

(2) Usually no callus developed from the upper cut of cuttings,
seedlings, and scions, whether cut off slanting or square. If any was
formed, it barely showed above the surface of the cambial layer.

(8) Under moist air conditions, either in moss, sand, sawdust, soil,
or in the open air, callus formed readily on the lower cut ends of cut-
tings, seedlings, and scions. In time it formed excessively developing
outgrowths half an inch or even more in diameter.

(4) In root grafts in time callus formed excessively under the con-
ditions mentioned in the preceding paragraph at the lower pointed
end of all the scions and at the lower cut ends of some of the roots in
the grafts (Pl. VIII, fig. 2). The graft union was closed with callus

186

48 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

in a short time, but, except as mentioned, the callus was usually con-
fined to the wounds and did not project beyond.

(5) Under very wet conditions, as in water, the formation of callus
was almost entirely inhibited in wounds, but lenticellular proliferations
were abundant from other parts of the surface of shoots and roots.

(6) The two regions where the formation of callus in root grafts
was most abundant, the lower point of the scion piece and the lower
end of the root piece coincide exactly with the position of more than
90 per cent of the galls occurring on root-grafted trees, indicating a
close relation between the formation of callus and the development
of the disease.

Fifty root grafts with large outgrowths of callus (Pl. VIII, fig. 2)
were selected from those in the experiment and the same number
with no excessive development of callus were selected. These were
planted in separate benches in a greenhouse in ordinary soil, not ster-
ilized. They all grew. Of the set with excessive callus 32.2 per cent
developed galls of the hard form. All of the other set grew into
healthy trees. This indicates that excessive callus formation either
is Incipient crown-gall or may develop into it. Storage conditions
should be such as to hinder the excessive development of callus.
Moist sand is the best medium of those tested for packing root grafts.

Studies on root formation as related to havry-root.—In connection with
the study of the formation of callus and under the same conditions,
an experiment was conducted for the study of root production on
healthy seedlings as compared with that on those diseased with hairy-
root and the woolly aphis. Seedlings of these three types were pre-
pared as in the former experiment and placed under the same con-
conditions of moisture.

It was found that as a rule no roots were produced from cuttings
or scions from the limbs of healthy apple trees under the conditions
of the experiment. Such was not the case with cuttings taken from
the tops of a number of apple seedlings badly diseased with the simple
form of hairy-root. Roots were produced freely from all of these
under moist conditions. Where healthy apple seedlings in which the
stem and root tip had not been cut off were kept in a cool condition
for two months and in a warm condition for one month, a few scat-
tered new side roots developed on most of the roots, but only shoots
or leaves developed from the stems. In the case of the seedlings dis-
eased with hairy-root which were placed under similar conditions,
abundant root formation, usually in clusters or tufts, took place from
tissues in or adjacent to. the diseased parts, not only from the roots
but often from the stems, and at the same time shoots were thrown
out from the root tips below diseased areas. This is a reversal of the

natural order of root and shoot formation in apple seedlings.
186

COMMUNICABILITY OF THE DISEASE. 49

A third set of apple seedlings was also placed at the same time
under the conditions of the experiment. This consisted of a number
of bunches of apple trees badly affected with aphis galls but showing
no hairy-root formation. It was thought that these seedlings with
galls might develop hairy-root, but they behaved in their rooting no
different from the set of healthy seedlings.

The relation existing between the woolly aphis, however, and the
aerial form (stem tumors) of hairy-root (Pl. V, fig. 2) is a subject for
future investigation. The following observation gives the reason:
In a seedling nursery in Indiana, mentioned on page 37, about forty
trees were found diseased with this form of hairy-root, and they were
also infested with the woolly aphis. It was noted that the trees
adjacent to the badly affected trees were contracting the disease,
indicating that this aphis may assist in the spread of the disease by
carrying the organism causing it.

No communication of the disease to healthy uninjured seedlings.—In
an experiment with healthy apple seedlings, described on page 16, it
was shown that healthy seedlings, uninjured as far as could be deter-
mined, failed to become diseased even when the soil about their roots
was mixed with finely chopped pieces of living soft and hard crown-
galls from apple trees. Thus, without wounds, there was no com-
munication of these forms of disease to apple seedlings. Where
wounds were made, other conditions being the same as before men-
tioned, 4 per cent of the trees became diseased with the hard form
of crown-gall.

The disease is communicable to wounded seedlings—A number of
experiments have been conducted with healthy apple seedlings grown
in the nursery and carefully washed and the tips of the roots cut off.
They were then divided into lots of approximately equal numbers and
prepared for the experiment as follows: The plants in one lot were
prepared for a control by making a slanting incision into the root and
then wrapping the wound with a thread in the same manner that
grafts were wrapped. A second control set was similarly treated,
except that a cross section of clean, healthy apple roots was inserted
in the wound before wrapping. A third set was prepared like the
first, except that a piece from the outside of a living apple crown-gall
of the soft form was inserted in the wound. A fourth set was prepared
similarly, except that a piece from the outside of a living apple crown-
gall of the hard form was inserted. A fifth set, consisting of a smaller
number of seedlings, was similarly prepared, except that a cross sec-
tion of a piece of living apple seedling diseased with the simple form
of hairy-root was inserted. After growing one season the results were
as given in Table XXIII, in the appendix.

50414°—Bul. 186—10 4

50 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

These experiments prove that soft crown-gall of the apple is com-
municable to some extent in wounds by inoculating with .pieces of
living galls, but that pieces of hard crown-galls and the simple
hairy-root may not readily communicate the disease under similar
conditions.

Increase of the disease in root-grafted trees due to the inoculation of
grafts.—In order to test the communicability of the soft form of apple
crown-gall, a set of nursery experiments was conducted. The grafts
were prepared from healthy scions from the varieties Red June,
Rambo, York Imperial, and Minkler, grafted on the roots of healthy
selected seedlings from trees grown from the same seed in the same
field. The grafts:were prepared in three lots: The first as ordinary
tongue or whip grafts; the second lot had a piece of clean cross section
of healthy apple seedling root inserted beneath the lower end or
tongue of the scion before wrapping each graft; the third had a piece
of living apple crown-gall of the soft form taken from the outside of
the gall and inserted under the lower end of the scion in each graft
before wrapping it. Each of the three lots of grafts was separated
into eight equal sets, which were planted and grown in three experi-
ments (1, 2, and 3) in the same localities and which were dug in the
‘same manner as the grafts in the experiments whose results are given
on page 62. The results of the experiment are given in Table XXIV,
in the appendix.

Briefly summarized, the results from the experiments are as follows:
Where a piece of living healthy root chip had been inserted in the
eraft union it caused an increase of crown-gall amounting to from 1
to 14.2 per cent and where a piece of tiving apple crown-gall had been
inserted there was an increase of crown-gall amounting to from 2 to
33.8 per cent as compared with the amount of crown-gall present in
trees grown under similar conditions from ordinary root grafts. In
the former case the average increase was 4.7 per cent and in the latter
12.6 per cent. The resulting disturbance did not vary the amount
of hairy-root present in either case.

On the whole, this set of experiments shows that crown-gall is com-
municable in root grafts if they have an opportunity to become
infected at the time the healing processes are taking place in the
union; or, in other words, at the time callus is formed abundantly in
the wounds.

The data in experiment 1 indicate not only that there is no further
spread of crown-gal! in the nursery rows the second and third years,
but that there is an actual decrease of the disease due to the recovery
of many trees. This must have taken place, since in experiment 1
every third tree was dug with spades the first year, the second year
one-half of those remaining also with spades, and the balance of the

186

COMMUNICABILITY OF THE DISEASE. yl

trees the third year, with a tree digger. In digging the trees with
spades those remaining were often wounded, and this alone should
have led to an increase of disease. In this and in all of the other
experiments mentioned in this bulletin conducted by the author he
personally examined the root grafts when made, directed the planting
and cultivation, saw every tree as it was dug, and noted in each case
the condition of the roots.

Increase of the disease due to poorly fitted root grafts.—In order to
determine the relation of defective grafting to the increase of crown-
gall in the nursery a number of experiments were conducted. Two
series of whip or tongue root grafts were prepared from the same lots
of scions and seedling roots. The varieties Gano, Wealthy, Red June,
Martha, and Whitney were used. The root grafts of one series were
carefully made, root and scion pieces of equal diameter being selected
and smoothly fitted at the union (PI. IX, fig. 2, A). The second
series consisted of similar grafts very poorly fitted in which either
root and scion piece were of different diameters or the end of the
one projected beyond the surface of the other (Pl. IX, fig. 2, OC
and PD).

These root grafts were planted in eight equal lots in experiments
1, 2, and 3 in cooperative plats 1 to 8 (for description see p. 78).
In experiment 1, four lots of grafts planted in cooperative plats 1 to 4,
every third tree was dug at the end of one season, every second at the
end of two years, and the remaining trees at the end of the third
year. In experiment 2, two lots planted in cooperative plats 5 and 6,
every other tree was dug at the end of the first season, and the remain-
ing trees at the end of the second year. In experiment 3, two lots
planted in cooperative plats 7 and §, all of the trees were dug at the age
of 2 years. Table X XV, in the appendix, gives the results from each
of the experiments.

A smaller experiment, similarly prepared, in which a number of
poorly fitted root grafts and twice as many carefully fitted grafts
from the same stock of scions and seedlings were made, was conducted
in eastern Missouri. The results of the experiment are as follows:
Out of a total of 357 trees grown from the smoothly fitted root
erafts, 7.8 per cent was diseased with crown-gall and 5.1 per cent
with hairy-root; and out of a total of 217 trees grown from the poorly
fitted root grafts, 17.5 per cent was diseased with crown-gall and 11.1
per cent with hairy-root, or a saving of 15.7 per cent on trees of a
marketable size due to smooth fitting.

Briefly summarized, the results of these experiments are as follows:
(1) Poorly fitted root grafts, as compared with carefully fitted
ones, yielded an increased percentage of diseased trees both with
crown-gall and with hairy-root. The increase of crown-gall in both

186

52 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

experiments varied from 1.2 to 41.7 per cent and of hairy-root from
1.8 to 6 per cent.

(2) The use of carefully fitted root grafts, as compared to poorly
fitted ones in both experiments, yielded an increased stand of trees.
This increase amounted to 21.6 per cent in the first experiment and
to 26.7 per cent in the second experiment. This was due to the
death of many more of the poorly fitted grafts just after planting,
before they struck roots.

In the case of the smoothly fitted grafts the superior stand of trees
is due to the more perfect union formed by the callus quickly estab-
lishing a circulation in the graft when it is planted in moist soil.
This brings about a more rapid healing and results in a higher vitality
and an increased stand of trees.

A poor fitting of root grafts also causes an increase of abnormal
callus, permitting a greater communicability of crown-gall during
the first year’s growth. This increase takes place chiefly at the time
the wounds of the graft union are healing. The same does not apply
so well to forms of hairy-root, which, as a rule, are not necessarily con-
nected with the graft union, but occur as often on other portions of
the roots of grafted trees.

What does this loss from poorly fitted root grafts mean to the
nurseryman? On the basis of 15,000 trees to the acre, a low estimate,
it means the loss of 2,355 marketable trees for every acre of apple
trees. If trees are valued at 8 cents apiece, it means the loss of
$188.40 per acre.

The use of scions from diseased trees uncreases the amount of disease.—
It has been the custom of some growers of grafted apple trees in the
central United States to grow their stock three years before market-
ing it. The yearling trees are cut back to near the ground, and the
tops are used for scions in making root grafts for the next season’s
planting. A portion of such scions must, of course, come from trees
with diseased roots. Some growers cut scions directly from cull
trees in the nursery bins, many of which are diseased with crown-
gall and hairy-root. Others plant these culls in their scion orchards
and later cut scions from them. ‘These three methods of selecting
scions must be condemned, since they tend to increase the number
of diseased trees grown from orchard grafts.

In order to test the effect of taking scions from trees with diseased
roots, a series of experiments has been conducted, in which scions
were taken from trees with both healthy and diseased roots.

The grafts in the first and largest experiment were planted in 1905.
The trees were dug in 1906, at the age of 2 years. In this experi-
ment the trees used were grown from root grafts made in equal number

from scions taken from healthy trees and from those diseased with
186

COMMUNICABILITY OF THE DISEASE. 53

crown-gall. The varieties used were Collins, Wealthy, York Imperial,
Gano, and Jonathan, planted and grown in independent plat 2 (see
p. 78). The results from this experiment are given in Table XXVI,
In the appendix.

The second experiment, in which the trees were dug in 1907, at the
age of 1 year, was made in independent plat 3 (see p. 78). The root
erafts were made with scions from both healthy trees and those
diseased with crown-gall and hairy-root. The results are given in
Tables XX VII and XXVIII.

The grafts of the last experiment were planted on the clayey soil
in independent plat 4 (see p. 78). The sets of root grafts were made
from scions taken from healthy trees and from those diseased with
crown-gall and hairy-root. The results of this experiment are given
in Tables XXIX and XXX.

These experiments show a decided increase of disease in root-
erafted trees grown from grafts made from scions from apple trees
diseased with crown-gall and hairy-root as compared with those
erown from scions selected from healthy trees. This increase in
the different experiments is as follows:

An increase of crown-gall in the first experiment of 2.2 per cent,
in the second of 7.4 per cent, and in the third of 7.2 per cent. An
increase of hairy-root in the first experiment of 7.1 per cent, in the
second of 12.5 per cent, and in the third of 16.3 per cent.

Although this increase is not very great, it is cumulative where
the process is repeated year after year, and is of sufficient importance
to deserve the careful attention of every nurseryman. All scions
should be selected from healthy trees, and the same observation will
no doubt apply to the selection of buds for budding where the twigs
are kept dormant in cold storage. To accomplish this means that
the scion orchard must be grown from healthy trees, and all diseased
trees should be removed from the scion orchard as soon as detected.

The spread of the disease from tree to tree in nursery rows is almost
negligible after the first year—In experimenting along the various
lines of the problem, a number of experiments were conducted so
that all conditions would be equalized as nearly as possible, and
a definite proportion of the trees grown in nursery rows was dug
each year for the purpose of noting the spread of the disease in the
rows from tree to tree. Three sets of such experiments, designated
as experimental sets 1, 2, and 3, were conducted in cooperative
plats 1 to 6.

In experimental set 1 seven duplicate experiments, each using grafts
from the same stocks of healthy scions and seedling roots, were
planted in four equal lots in cooperative plats 1 to 4. One-third of
the trees grown from these root grafts were dug at the end of one year,

186

54 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

digging every third tree; one-half of the remainder, or each alternate
tree, were dug at the end of the second year, and the remaining trees
were dug the third year. The combined results from these experi-
ments are given in Table XXXI, in the appendix.

In experimental set 2 the conditions in set 1 were duplicated and
the grafts planted in cooperative plat 6 in 1905. One-third of the
trees, as before, were dug at the end of the first year, but at the end
of the second year it became necessary to dig the remainder on
account of the more rapid growth of the trees in this locality. The
results from this experiment are given in Table XXXII.

In experimental set 3 the conditions of set 1 were duplicated and
the grafts planted in cooperative plat 5 in 1905. One-half of the
trees, selecting each alternate tree in the row, were dug at the age of
2 years and the remainder at the age of 3 years. The results from
this experiment are given in Table XXXITTI.

The results from the three sets of experiments are summarized as
follows:

(1) They show a decrease of crown-gall in trees in nursery rows
after the first year; in set 1 a decrease from 26.7 per cent the first
year to 9.1 per cent the second and to 4.7 per cent the third; in set 2
from 20 per cent the first year to 12.8 per cent the second; in set 3
from 11.7 per cent the second year to 2.6 per cent the third.

(2) They show a general and decided increase of hairy-root the
second year, with a slight or no increase the third. In set 1 there
Was an increase from 5.5 per cent the first year to 8.6 per cent the
second and 8.7 per cent the third; in set 2 from 7.9 per cent the
first year to 10.3 per cent the second; in set 3 from 6.4 per cent the
second to 10.2 per cent the third year.

(3) The increase in hairy-root does not nearly offset the decrease
in crown-gall and some of the trees must throw off the disease and
recover. In set 1 crown-gall decreased 22 per cent, while hairy-root
increased but 3.2 per cent. In other words, the number of diseased
trees decreased 18.8 per cent. In set 2 crown-gall decreased 7.2
per cent, while hairy-root increased 2.4 per cent, and of diseased trees
there was 3.8 per cent less. Im set 2 the percentage of crown-gall
decreased 9.1, while that of hairy root increased 3.8, and of diseased
trees there was a decrease of 5.3 per cent.

In conclusion, the time when the disease is communicated to the
trees is during the first year. In the light of experiments already
described the communicable period must be during the time of the
formation of callus for closing the wounds in the union of scion and
root.

These experiments show that crown-gall as a rule does not spread
from tree to tree in the nursery after the first year and that hairy-root

186

— ee ee
SIE a a - — —— —- $$
‘

COMMUNICABILITY OF THE DISEASE. 55

increases considerably from the first to the second year, and but
slightly the third year. |
The disappearance of crown-gall is considered to be due to two

causes: (1) Some of the hard galls throw out roots and develop

into woolly-knot, while (2) a much larger number of galls gradually
disappear as the tree increases in size, and such trees must recover
from the disease.

In closing the discussion of this subject it should be noted that the
results given here are from seven parallel sets of experiments in six
localities, or forty-two parallel experiments in five States, and include
data on 31,886 trees. The results might not have been the same in all
localities in the United States, but certainly fairly represent typical
nursery conditions in the heart of the apple-growing belt in the central
States of the Mississippi Valley.

Pruning and grafting knives are not responsible for much of the
disease.—In view of the fact that it has been asserted that crown-
gall is largely communicated by the use of pruning and grafting
knives, 100 carefully selected seedlings from the nursery were
washed, thoroughly dried, and planted in sterilized soil in a green-
house (p. 77). Before being planted a downward cut on the root
near the ground line was made with a grafting knife which had in
each instance just been used in making a cut in a live soft apple gall.
The greatest care was exercised to see that the knife used in making
the cuts in the seedlings was in each case passed back and forth
through a fresh crown-gall before the cut was made. For compari-
son, 100 healthy seedlings from the same stock were planted after
being carefully washed and dried. Before planting, a cut was made
in each of these seedlings as before, except that in each instance
the knife blade was dipped in a one-tenth per cent corrosive-sub-
limate solution before making the cut. At the end of the growing
season 4 per cent of the control seedlings had developed crown-gall
and only 2 per cent of those that had been wounded with the gall-
infected knife were similarly diseased. This experiment fails to
confirm the belief that the grafting knife is responsible for much of
the crown-gall present in root-grafted stock in the nursery.

Crown-gall not readily communicated to dormant trees. stored in
bundles.—The communicability of crown-gall by contact of healthy
trees with diseased ones while tied in the same bundle has been the
subject of much dispute, especially between nurserymen and nursery
inspectors.

The experiments conducted in cooperative plat 6 in 1905 may
throw some light on this subject. Two sets of seedling apple trees,
100 in each, were inoculated with chips of living soft galls from

186

56 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

apple trees inserted into slanting incisions in the roots and tied
with grafting thread. One set was prepared about six weeks before
planting and kept dormant by being stored in moist excelsior in a
cool place; the other was prepared in the same way as the first and
planted out immediately. For each set an additional set of-an
equal number was wounded and wrapped with thread without
inoculating. All were grown one year. Of the inoculated stored
seedlings, 7.4 per cent became diseased with crown-gall; of the
control, 4.3 per cent, chiefly of the hard form; of the inoculated set
planted immediately, 34.1 per cent became diseased with crown-
gall, chiefly of the soft form; and of the control, 2.9 per cent, chiefly
of the hard form.

In a second experiment, 500 root grafts were prepared from healthy
scions of Wealthy grafted healthy seedling roots as a control set.
A similar set of 500 grafts was prepared by rubbing the tongued end
of both the scion and the root pieces on the freshly cut surface of a
living soft gall from an apple tree before joining together the cut, a
number of galls being used. These were planted in the nursery after
being stored for six weeks in separate boxes in a cool cellar. At the
end of one season’s growth there was approximately the same amount
of disease in the control as in the inoculated sets, the control ‘con-
taining about 19.5 per cent of trees diseased with crown-gall, and,
the inoculated set 21 per cent, both chiefly of the hard form. |

The results of the these experiments indicate that the communica-
tion of crown-gall to wounds in apple trees is a variable factor and
that the contact of wounded living galls with wounded surfaces
when dormant may result in little or no infection, but that under |
erowing conditions, where callus is formed abundantly, such as
resulted at once where the seedlings were inoculated with pieces of
living apple galls and planted immediately, the disease was com-
municated readily. In these seedlings growth, with the formation
of callus, took place at once, favoring the entrance of the organism.
In the case of the stored seedlings and grafts, owing to the low temper-
ature, the formation of callus was retarded at least one month before
it became warm enough for its development.

In the writer’s opinion, given in the light of the results of these
and other experiments recorded in this bulletin, crown-gall is com-
municable by contact only in wounds where fresh callus is being
formed. Where trees are dormant there is little danger of communi-
cation.

The disease only slightly communicable in orchards.—Reference will
again be made to orchards 1 and 2, already described. <A statement
of the condition of the trees in these orchards at the beginning of the

186 .

COMMUNICABILITY OF THE DISEASE. ul

experiment and six years later, when the trees were dug, is given in
Tables XXXIV and XXXV, in the appendix.

The results from the experiments, as shown in Tables XX XIV and
XXXV, are as follows: The orchards were planted with trees 50.1
per cent of which were diseased with crown-gall. At the close of
six years 40.5 per cent of the original number of trees was diseased,
of which 15.8 per cent was diseased with crown-gall and 24.7 per
cent with hairy-root.

Of 416 trees alive at the end of six years, 226, or 54.3 per cent,
were healthy, as compared with 49.9 per cent of the original number.

In order to further analyze the results of the experiment, Tables
XXXVI and XXXVII are given, with the separate record of the
healthy and diseased trees in each plat.

From these tables it will be seen that, after deducting the dead
trees, 1 out of the 83 healthy ones in orchard 1 had become diseased
with crown-gall and 18 with hairy-root; and out of the 70 healthy
trees in orchard 2, 10 had become diseased with crown-gall and 29
with hairy-root; but it was noted at the time of digging that in
every case the amount of disease on the newly infected trees was
slight, the badly diseased trees in the plat after six years being
few in number and among those that were originally diseased. In
comparison with this increase of disease it must be noted that, after
deducting the number of dead trees, out of 96 diseased trees planted
in orchard 1, 32 fully recovered and out of 139 diseased trees planted
in orchard 2, 41 recovered entirely. In other words, where 58 trees
became slightly diseased, 11 with crown-gall and 47 with hairy-root,
73 trees recovered from crown-gall during the same period without
any treatment whatever.

This slight communicability shown by traces of disease is cer-
tainly almost negligible from the standpoint of the orchardist and
must have occurred during the first growing season, since great care
was taken not to wound the trees by cultivation. The experiment
certainly indicates that apple trees when they are once established
are not in danger of becoming seriously diseased on the roots if
cultivated carefully and without imcurring wounds, even when
every tree 9 feet away in the adjacent rows is diseased, as in the
experiment. There appears, then, no need of removing diseased
trees from orchards, except when they are not doing well; that is,
when they show every indication of becoming unprofitable or when
there is danger of communicating the disease to valuable small fruits.
The matter of communicability as it applies to other apple trees in
the orchard need hardly he considered when the question of removal
is being taken into account.

186

58 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

PREVENTION AND CURE.
PROBABLE FUTILITY OF ATTEMPTS AT PREVENTION.

Numerous recommendations have been made from time to time
by plant pathologists and others looking toward the prevention of
crown-gall by the removal of supposed sources of infection. These
recommendations were made not specifically for the apple disease but
for crown-gall in general. Advice has generally been given to obtain
nursery trees as far as possible from nurseries free from disease. It
has generally been considered that the planting of trees affected with
crown-gall and hairy-root is liable to give rise to diseased trees
throughout the orchard. In spite of the most vigorous nursery
inspection for a number of years in many States the disease on apple
trees is quite generally disseminated throughout the United States,
and the writer knows of no apple-growing nursery that is entirely free
from the forms of disease described in this bulletin.

Although much advice has been given for the prevention of the
disease, little in the way of successful experimentation along this line
has been done hitherto. Butz (7) planted healthy trees in infected
land to which finely powdered sulphate of copper had been added.
On account of the death of most of the trees, attributed to a serious
drought, he was unable to make any generalization regarding the
efficiency of this treatment. Sulphur used by him in the same way
had no effect in retarding the disease.

Popenoe (45), in speaking of attempts made by growers in Kansas
to prevent loss by apple crown-gall, says:

It has been the hope of some nurserymen to prevent the large percentage of loss
from diseased stock by planting their apple grafts in localities and soil not before
in apple trees, but in some notable cases coming under my observation within the
last few years this endeavor has failed signally of the object.

The writer personally knows of similar experiences by nurserymen
in a number of localities in Kansas, Nebraska, Missouri, and Iowa.

The writer has conducted a number of experiments along the line
of prevention and cure. Some of these have resulted in materially
lessening the amount of disease present in nursery stock. The results
will be given, in the hope that they will effect a great saving not only
to nurseymen.but to orchardists as well.

As a result of many observations in nearly three-fourths of the
States in the Union the writer is of the opinion that the crown-gall
organism is so widely disseminated that any system of eradication
must fail.

In discussing methods to control and limit the formation of crown-
gall and hairy-root on apple trees in nurseries and orchards, the
the subject-matter will be brought under two general headings, one

186

PREVENTION AND CURE. 59

dealing with methods for the control of the disease in the nursery,
and the other with methods for its control in the orchard.

METHODS FOR THE CONTROL OF THE DISEASE IN NURSERY BINS.

Since it has been found that apple crown-gall is communicable, and
can be transferred from the apple to the stone fruits, the raspberry,
the blackberry, the rose, the grape, ete., and vice versa, nurserymen
should at the time of digging pick out and remove all plants diseased
with crown-gall. They should not be tied in bundles with other
plants, owing to the slight possibility of transferring the disease to
healthy wounded plants. In the case of apple-root grafts it has
been shown that they are most susceptible at the time the graft is
forming callus and is uniting. Care should be taken to keep the
nursery bins, especially where material for root grafts is kept, free
from diseased plants. It is best to clean all nursery bins and thor-
oughly spray them with a strong solution of copper sulphate each
_year before the time for storing trees for the winter.

PROPAGATION OF SUSCEPTIBLE VARIETIES OF APPLE TREES BY
BUDDING.

It has been shown elsewhere in this bulletin that in most sections
of the country where apple trees are propagated, both by budding
and by root grafting, budded trees are freest from disease. For this
reason it is advisable to propagate those trees most subject to crown-
gall and woolly-knot by budding. There is an objection offered to
budding on account of the necessity for growing the trees a year
longer. The additional cost for this extra year may be more than
offset by the increased number of healthy trees obtained by this
method. The additional loss from woolly aphis during the last year
of growth in the nursery is asserted by many nurserymen to be so
great in some localities as to preclude budding. If such nurserymen
will consult with the Bureau of Entomology of this Department as to
the proper method of combating and controlling this troublesome
insect pest by fumigation, etc., means will be found by which this loss
may be greatly diminished, and propagation by budding in the case
of varieties susceptible to crown-gall will become profitable.

IMPROVEMENT IN METHODS OF ROOT GRAFTING.
SELECTION OF HEALTHY SCIONS NECESSARY.

In the control of any disease that might be transmitted through
root grafts it is perfectly logical to demand that the pieces, both
scion and root, that are built into the root grafts should be healthy.
It has been shown on page 23 that there is an increase in disease due
to taking apparently healthy scions from trees whose roots are dis-

186

60 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE,

eased. Growers of root-grafted trees will make no mistake if they
insist on getting scions from strictly healthy trees, and they should
grow their own healthy scions if possible.

SELECTION OF HEALTHY SEEDLING ROOTS NECESSARY.

The selection of healthy seedling trees from which roots are to be
taken for root grafts is of prime importance to the grower. It has
already been shown by experiment that the selection of roots from
seedling trees diseased with hairy-root often results in the growth
of a tree with diseased and deformed roots (Pl. VII, figs. 3 and 4),
one which is unmarketable, even though in many cases it would no
doubt develop into a profitable tree in the orchard. It is not profit-
able to grow diseased trees or to be the distributor of diseased stock.

It has also been shown by experiment that it is not best to use
the apparently healthy portion of a seedling root which bears a soft
gall. The use of such stock will certainly result in an increase of
this form of disease and can not be profitable.

Finally, it must be said to growers of seedling apple trees that
when the seedlings are dug, all rough, warty, hairy, or tufted seed-
lings should be rejected and destroyed (PI. III, fig. 1, and Pl. IX, fig.
2,G@and H). Asa matter of precaution, they should not be tied up
with healthy seedlings. Nurserymen purchasing seedlings for mak-
ing root grafts should insist on this.

CAREFUL FITTING OF ROOT GRAFTS NECESSARY.

The influence of a projecting scion in the formation of excessive
callus and the liability of such callus through infection to develop into
crown-gall has already been discussed. It will pay nurserymen to put
a premium on neat, close-fitting tongue grafts made at a reasonably
rapid rate rather than to encourage the rapid manufacture of a
poorly-fitted graft with the scion projecting at the union or with one
made too blunt at the lower end, such as are shown in Plate IX,
figure 2, C and D. The best results with the least amount of dis-
ease will be secured by the use of No. 1 unbranched seedling roots
upon which there have been closely and smoothly fitted scions of
equal diameter, properly wrapped. The stress of competition in
recent years has led to increased carelessness in the manner in which
root grafts have been put together and to the use too often of inferior
roots and scions.

EXPERIMENTS ON THE BEST METHODS OF WRAPPING ROOT GRAFTS.

Mention has been made of the tendency of root grafts to form
excessive callus at the lower tip of the scion when stored under moist
conditions in sawdust, excelsior, moss, and other similar materials.
Where the two pieces of the graft are snugly fitted, there is little

186

PREVENTION AND CURE. | 61

tendency for the callus to form anywhere except in the intervening
-spaces. When the pieces are more or less imperfectly fitted and are

not firmly held together, especially at the lower end of the scion, there
is a tendency for the callus to grow out into the air, forming thick
cushions (Pl. VIII, fig. 2) or gall-like outgrowths. The wrappings
were planned to confine this formation of callous and to hasten the
union between scion and root pieces.

In order to find a method of controlling the formation of callus,
25,200 root grafts were wrapped with various materials (Pl. VIII,
fig. 1) during the winter of 1904-5. The idea of wrapping root
erafts is not a new one, since nurserymen used both waxed cloth and
waxed paper for many years before the present method of thread
wrapping came into vogue.

All of the grafts made for the experiment were of the type known
as “whip” or ‘‘tongue”’ grafts. They were especially well made
from No. 1 Kansas roots, fitted with a selected lot of scions from
each of the following varieties: Winesap, York Imperial, Wealthy,
Missouri, and Northern Spy. They were made in February, packed
in moist, chopped excelsior, and stored in a cool place for about six
weeks.

The manner in which the wrapping was made and the material
used may be briefly described as follows:

Wrapping with cloth—The cloth used was a cheap black calico of
the poorest grade obtainable in the market. (See Pl. VIII, fig. 1, C.)
This was torn into strips 1 inch wide and 4 or 5 inches long. After
the graft was made one end of the cloth was dipped for one-half inch
into hot, melted grafting wax. Starting with the other end, the
cloth was then wrapped tightly around the scion and the free waxed
end pressed down. This completed the operation.

Wrapping with rubber—The rubber used was of a quality similar
to dental rubber, which is also frequently used for insulating wires.
(See Pl. VIII, fig. 1, #.) It was bought in rolls 1 inch wide and was
cut off in such lengths as were necessary to completely envelop the
union. The rubber was usually wrapped so as to encircle the union
twice, and the free end was fastened with rubber cement applied
with a brush.

Wrapping with waxed paper.—Sheets of ordinary unglazed printers’
paper were waxed on one side by coating them with hot grafting wax
applied with a paint brush. (See Pl. VIII, fig. 1, G.) They were
then cut into I-inch strips, ten to twenty sheets being cut at one
time, and these again into strips about 4 or 5 inches long. One paper
strip was then wrapped around the union, the waxed side toward the
graft, the free end being stuck down by pressing on it.

Wrapping with plain thread—The thread used for the ordinary
erafts was machine cotton No. 9. (See Pl. VIII, fig. 1, A.)

186

62 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREBR.

Wrapping with waxed thread.—The waxed thread used was machine
cotton No. 28. This was soaked in hot grafting wax until thor-
oughly penetrated and was then allowed to drain while hot. (See
fle VEE hes DS)

Waxing the union.—Ordinary grafts were made with plain thread,
wrapped as previously described, and then the union of scion and
root was coated with melted grafting wax nearly at the point of
hardening. (See Pl. VIII, fig. 1, B.)

Unwrapped grafts —The grafts left without wrapping of any kind
were made with special care, so that when the roots and scions were
joined they remained quite firmly united. (See Pl. VIII, fig. 1, F.)

Results of ecperments.—As these root grafts were made they were
divided into eight equal duplicate sets. One set was planted in April,
1905, ineach of the cooperative plats 1 to 8. (For description see p.
78.) All plats showed a fair stand in November, 1905. The trees
grown from these grafts made with No. 1 seedlings and scions corre-
sponding in diameter were from the beginning larger and more vigor-
ous than any other lot of trees planted at the same time in other
parallel experiments in which No. 2 seedling roots were used. This
was the case even where scions of the same varieties were used.
This proves that No. 1 seedlings are the best for root grafting.

In cooperative plats 1 to 4, one-third of the trees were dug at the
end of one year, taking every third tree in each row; one-third at the
end of the second year, taking each alternate tree in the row; and the
remaining trees at the end of the third year. The results from these
plats, designated as experiment 1, are given in Table XX XVIII, in
the appendix.

Of the trees in cooperative plat 6, one-third were dug at the end
of one year, taking every third tree in each row, and the remaining
trees at the end of two years. The results from this plat, designated
as experiment 2, are given in Table XXXIX.

Of the trees in cooperative plat 5, one-half, taking each alternate
tree in the row, were dug at the end of the second year and the remain-
ing trees at the end of the third year. The results from this experi-
ment, which is designated as experiment 3, are given in Table XL.

All of the trees in cooperative plats 7 and 8 were dug at the age of
2 years. The results from these plats, designated as experiment 4,
are given in Table XLI.

In order to show the general results from each kind of wrapping
on 1-year-old, 2-year-old, and 3-year-old trees, the results from the
four experiments are combined in Table XLII.

Finally, the results of the four wrapping experiments in cooperative
plats 1 to 8 are summarized in Table XLIII for convenience in com-
parison and in summing up the results,

186

PREVENTION AND CURE. 63

There were planted 3,600 root grafts with each kind of wrapping.
The percentage of healthy trees grown from each set, given in order
from the highest to the lowest, is as follows: Cloth, 78.2; rubber,
71.4; waxed paper, 62.5; waxed thread, 60.5; plain thread, 60.3; no
wrapping, 49.6; and wax covered, 28.5.

The results from this series of experiments are comparable, con-
sidering the varying physical conditions of the plats in which the
trees were grown, since other conditions were similar. There is but
a slight variation in the experiments in the percentage of trees dis-
eased in the case of each kind of wrapping. It is for this reason that
the results from each experiment are given separately.

The conclusions taken from the experiment as a whole are these:
Cloth is the best wrapping to use. Rubber is almost equal to cloth,
but its cost is prohibitive. Waxed paper is a little better than
ordinary thread wrapping, which is again better than waxed thread.
The other two methods are not worth considering.

The percentage of trees in each set lost by disease, considering each
diseased tree as a cull, is as follows: Cloth, 12.1; rubber, 15.7; waxed
paper, 22; plain thread, 25; waxed thread, 28.6; no wrapping, 31.5;
and wax covered, 38.2. These percentages do not include the root
grafts that died.

The best way to consider the results of the experiment from the
nurseryman’s standpoint is to estimate the number of healthy trees
to the acre that would be obtained by each method of wrapping. Not
nearly all root grafts that are planted grow. Many die before they
strike root, owing to various causes, such as the breaking of the callus
in the union by careless bundling, poor soil, and conditions at the
time of planting, etc. If 15,000 root grafts are required to plant an
acre, the number of healthy trees to be obtained from each kind of
wrapping, on the basis of the results from this experiment, is as
follows: Cloth, 11,730; rubber, 10,610; waxed paper, 9,375; waxed
thread, 9,075; plain thread, 9,045; no wrapping, 7,440; and wax
covered, 4,275.

If apple trees are worth 8 cents each wholesale, the gain from
the use of cloth wrapping as compared to the ordinary plain thread
wrapping is 2,685 trees, or $214.80 per acre.

Attention is called to the fact that to get the best results any
wrapping must hold the parts firmly together and that the union
should be entirely covered, especially the lower end of the scion piece.
It should also be noted that the cloth used was not waxed cloth, but
ordinary cloth, a cheap calico without wax, except to fasten down
the end. Waxed cloth may serve its purpose in preventing excessive
formation of callus and in keeping out germs, but often does not rot

186

64 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

away soon enough to prevent a constriction of the tree at the point
of wrapping.

It is suggested where cloth or cheap calico is used for wrapping
that sections of the proper width be cut from the end of a bolt of
cloth, using an ordinary lever paper trimmer, such as is found in
printing shops. This will give narrow strips of cloth which can be
placed on a reel in front of the wrapper. In nursery practice it has
been found best and quickest to secure the end of the cloth after
the graft has been wrapped by tying it with a half hitch instead of
waxing it down. In no case should the cloth or any other wrapping
be secured by drawing it under the end of the scion tongue, because
anything placed at this point will act as a disturbing element and
tend to increase the formation of callus and to permit the develop-
ment of crown-gall.

LATER EXPERIMENTS IN WRAPPING ROOT GRAFTS.

A number of nurseries tried wrapping with cloth in 1908, and all
that have reported to this office obtained good results. Some also
report good results with waxed cloth and waxed paper.

Some nurserymen use raffia in place of thread for wrapping root
grafts with good success. The method they use in wrapping is shown
by Plate VIII, figure 1, 7. In a small experiment in a greenhouse
in 1906 raffia was found to be equally as good a wrapping as cloth
when used as shown in Plate VIII, figure 1, H. There are two objec-
tions to the use of either cloth or rafia. The first is the increased ex-
pense of wrapping; the second is that neither is applied by the ordinary
wrapper, who is usually a boy, in aneffective manner. The lower
end of the scion is often not bound down closely, allowing the for-
mation of abundant callus and defeating the very purpose for which
the cloth and raffia are intended.

As to what constitutes an ideal wrapping for root grafts the writer
has repeatedly put himself on record in these words:

An ideal wrapping should hold the root and scion pieces together firmly till the
root graft has been planted in the nursery row. It should then rot quickly away.

The superiority of cloth as a wrapping has resulted in the invention
by two different persons, one in Missouri and one in Alabama, of a
continuous thread wrapping for grafts, which is applied evenly and
closely over the surface of the union, just as thread is wound on a
spool, and which is apparently superior to either cloth or raffa.
(See Pl. IX, fig. 2, B.) In 1908 a test was made of this continuous
thread wrapping for root grafts in comparison with the ordinary
thread wrapping. (See Pl. IX, fig. 2, A.) Five hundred apple grafts
were prepared in each manner, using scions from the Wealthy apple, a
variety very susceptible to crown-gall and hairy-root. The grafts

186

PREVENTION AND CURE. 65

were planted on the Arlington Experimental Farm of this Depart-

ment and grown for one season in a moist, stiff, heavy, clayey soil.
The results were as follows:

Of a total of 470 trees grown from grafts with continuous fine thread
wrapping, 38.1 per cent was diseased with crown-gall and 16.8 per
cent with hairy-root. Of a total of 419 trees grown from grafts with
ordinary fine-thread wrapping, 48.7 per cent was diseased with
crown-gall and 25.2 per cent with hairy-root. This is a difference
of 19 per cent in favor of the new thread wrapping, aside from an
increase in the stand of 10.2 per cent, indicating that it will probably
prove to be as good as cloth, if not better. The new thread wrapping
when applied with a machine made for the purpose can be used with
far greater rapidity than any wrapping hitherto in use, and as it
holds the union more firmly together it is destined, for thie reason
alone, to supersede the ordinary wrapping.

None of the forms of wrapping mentioned will prevent the forma-
tion of galls and of woolly-knot on the scion of a root graft above the
union, since these occur above the wrapping, especially in such varie-
ties as the Wealthy (PI. II, fig. 3). In the case of Wealthy trees,
such occurrence of disease on the scion often equals, or even exceeds,
that at the union, as was noted in the foregoing experiment. To
reduce this loss, budding or top-grafting must be resorted to, since
wrapping reduces only the disease occurring on the union. In the
nursery top-grafting is not practicable, owing to the amount of time
that it consumes. The additional labor adds to the expense, so as
to make the process unprofitable for the grower; not so with the
orchardist who grows a few trees and who wishes to take the time.
The Walbridge is a good, vigorous-growing tree, quite free from
crown-gall, and is recommended as a good sacle for top-grafting
with the Wealthy in an orchard. The Walbridge and the W ealthy
are hardy with reference to cold, and such a combination of scion
and rootstalk should do well in hie northern apple-growing States
in the Mississippi Valley, such as Nebraska, Iowa, and other States
in the same latitude.

THE USE OF WEAK ANTISEPTICS FOR THE PREVENTION OF DISEASE IN
ROOT GRAFTS OF DOUBTFUL VALUE.

At various times a number of nurserymen have tried dipping
scions and seedling roots in weak solutions of copper sulphate,
either before or after making them into root grafts. Those who
have experimented have reported little or no results in the prevention
of disease.

In order to test the use of copper svi. an experiment was
conducted with two equal sets of root grafts, planted, prepared, and

50414°—Bul. 186—10——9

66 THE CROWN-GALL AND HAIRY-ROOT. OF THE APPLE TREE.

grown under the personal supervision of the writer. Both the scions
and the seedling roots were grown in Virginia. The reason the
stock was obtained from Virginia is that certain writers have in-
sisted that most of the crown-gall comes from the West, especially
from Kansas. Scions were taken of the following varieties: Wealthy,
Gano, and Northern Spy. Before cutting it up into pieces for the
root grafts two-fifths of the stock, both scions and seedlings, were
dipped and thoroughly washed in a 2 per cent solution of copper sul-
phate in water. The grafts were made in the ordinary manner of
making commercial whip grafts, except that care was used in fitting
the scion and root pieces together. The results of the experiment
are given in Table XLIV, in the appendix.

The results show a considerable decrease of crown-gall and hairy-
root (13.8 per cent) in the case of the trees grown from disinfected
stock, but this is more than offset by the decreased stand, which was
less than one-half of that of the untreated trees. It is quite probable
that there was enough copper sulphate present to interfere with the
formation of the union in the graft, and it may yet be found that the
use of a more dilute solution will prove beneficial. The experiment
at least paves the way for further experimentation along this line
with less concentrated solutions. Many of the scion pieces treated
in the experiment died, while the seedling roots lived, thus indicating
an imperfect formation of callus in the union, probably due to the
action of the poison.

PACKING AND STORING ROOT GRAFTS.

There can be no question but that the packing and storing of root
grafts before planting are of vital mportance in the prevention of
disease. Care should be taken to use fresh new packing for this
purpose, avoiding the use of material or boxes which have been used
for packing trees that may have been diseased. The time of forma-
tion of callus in the root graft is the most critical in the growth of the
tree, and for this reason the grafts should be cared for with the
greatest solicitude.

In order to prevent the excessive formation of callus, which pre-
disposes the grafts to attacks of the disease, it will be necessary to
follow one of two procedures. The best method is to pack the grafts
in clean moist sand, and after a few days’ favorable growing tempera-
ture store them in cold storage but slightly above freezing, keeping
them there until planting time. Good results may be obtained by a
second method, in which a cool cellar is used for the immediate storage
of root grafts as fast asthey are made. This method answers well if
the temperature of the cellar can be kept at about 40° to 45° F., so
that callus will form very slowly and the growth of shoots and roots
will be held back.

186

PREVENTION AND CURE. . 67

For the proper development of callus in apple grafts, as already
mentioned, it was found that sand was the best material for packing.
The materials used in the experiment were steam sterilized. It will
not be easy to thoroughly sterilize sand in the nursery unless improved
machinery is invented, but with a little ingenuity in the arrangement
of perforated steam pipes through the sand container, whether it be
a box or a bin, most of the sand in use can be sterilized. Moss or
excelsior can wate be sterilized more or less thoroughly by putting
it in a barrel or box and passing through it live steam from a pipe.
This will rid the packing material of fungi, a number of which are
found attacking grafts improperly stored. Two such fungi are cer-
tainly species of Botrytis and Fusarium.

TIME OF PLANTING ROOT GRAFTS.

Tf root grafts are put in cold storage they can be held in good
condition till the proper time for planting in the spring. If the
facilities for holding back growth in root grafts are poor, then early
planting is necessary. Do not allow the root grafts to form exces-
sive callus and start to grow (Pl. VIII, fig. 2). In the writer’s
experiments the highest percentage of crown-gall occurred under
such conditions.

CARE IN THE CULTIVATION OF TREES IN THE NURSERY.

It has been shown that root grafts acquire crown-gall chiefly
during the first season’s growth and that much of the crown-gall
(Pl. II, fig. 3) and woolly-knot (Pl. VI, fig. 5) on certain varieties,
such as the Wealthy, occurs on the scion portion of grafted trees
near the surface of the soil. An examination of such galls usually
shows the presence of a wound in the tissues at the base of each.
This wound was evidently made with a hoe in cutting out weeds in
the row while the trees were young. For this reason care should be
taken to avoid wounding trees in cultivation.

When apple seedlings have been budded care should be taken not
to ridge the dirt about the trees until the bud wounds have at least
partially healed. If the trees are cultivated immediately after bud-
ding, crown-gall is often communicated to the callus forming in the
fresh wound. It is better to cultivate a short time before budding
rather than just after.

SELECTION OF HEALTHY TREES FOR THE SCION ORCHARD NECESSARY.

The matter of securing healthy scions for root grafting is impor-
tant, as has been shown by the experiments with apparently healthy
scions taken from trees with the roots diseased with crown-gall and
hairy-root. It was shown that the use of such scions increased the
amount of disease present in root-grafted trees (see pp. 23 and 25).

186

68 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

The planting of cull trees in the scion orchard can not be too
strongly condemned, since the greater number of such trees are dis-
eased with forms of crown-gall and hairy-root. Only healthy, vig-
orous trees should be planted in the scion orchard. Any tree in
such orchards that shows even a trace of disease should be removed.
A scion orchard should be used only as long as it is healthy and vig-
orous; then it should be replaced by a new orchard.

SELECTION OF THE BEST KINDS OF SOIL FOR GROWING TREES.

It is well known to experienced nurserymen that only certain tracts
of land in any locality are suitable for growing trees. It has been
strongly indicated by the results of the writer’s experiments that
heavy, wet, clayey soils increase the amount of crown-gall present,
and that trees on many well-drained soils show the least disease.
In general the light, loamy, well-drained soils, where fertile, are the
best for growing apple trees with a minimum of disease.

CURE OF DISEASED TREES IN THE ORCHARD.

Expervments by others.—When an apple tree has become diseased
with crown-gall and hairy-root it is a question as to whether any
curative method can be used to insure a healthy growth. Some
writers, notably the following, have advocated cutting off the tumors:

Howard (24), of Missouri, carried out the most extensive experi-
ment in an attempt to cure crown-gall. He studied the subject for
two years, employing many different remedies and combinations and
experimenting with nearly 3,000 trees. He used the following: Cop-
per sulphate (bluestone), iron sulphate (copperas), sodium chlorid
(common salt), lime, sulphur, formalin, ammonia water, bichlorid of
mercury (corrosive sublimate), copper carbonate, carbolic acid, hy-
drocyanic acid, potassium dichromate, mercuric cyanid, silver
nitrate, gas tar, kerosene oil, Bordeaux mixture, and hot water.

The remedies were used in three ways: By dipping the roots in
the materials; by sprinkling the soil with the solutions until the
‘surface was wet just as trees were being planted; and by cutting
away the galls and covering over the wounds with the materials to
prevent their growing again. Howard’s results show that some of
the compounds did prevent -the growth of the galls, but not without
injury to the tree. He says that ‘“‘copperas, bluestone, and lime
mixed together and applied to the wound was the best remedy of all
for preventing a new growth of galls, although this was not entirely
efficacious.” He mentions no control in which the galls were removed
without treatment with fungicides.

Butz (7), in Pennsylvania, took 60 apple trees and cut off the galls
from 40, one-half of which he dipped in Bordeaux mixture before

186

PREVENTION AND CURB. 69

planting; the other 20 were planted without removing the galls,
after dipping in Bordeaux mixture. After two seasons of growth,
in which none of the trees died, no result from the treatment was
obtained, as all of the trees still showed the disease.

Clinton (8) reports as follows from Connecticut:

In 1899 Doctor Sturgis set out on the station grounds ten young trees affected with
knots; part of these had the knots cut off, others had knots cut off and roots then
treated with copper sulphate, and some were left with knots on. After three seasons
of growth these trees were dug by the writer and the roots carefully examined. Very
little difference could be seen in any of the trees at this time, and the knots had
spread very little, if any.

Norton (37) says: ‘Apple trees slightly affected, often apparently
recover and make good trees, but even then the life of the tree may
be cut short and the ground infected.”

Garman (15) advocates the removal of the diseased parts with a
knife, but does not consider this treatment satisfactory, as it is
kas to weaken the tree.

Alwood (2), experimenting with seven trees, from which he cut
off the galls, giving the trees a subsequent treatment with strong
Bordeaux mixture, found that several of them showed a characteristic
erowth of crown-gall; two made a more normal growth.

Recommendations for the treatment of the disease in orchards.—The
question as to whether it is advisable to remove the galls from trees
in an orchard depends, first, upon whether the presence of the gall in
itself is of greater injury to the tree than the effect of the wound re-
sulting from its removal combined with that of the antiseptics used
for treating the wound; and, second, upon the danger of the disease
spreading to other trees. In an apple orchard, from the results of
the writer’s experiments, it appears that there is no danger of a
serious spread of this disease to other apple trees.

There is very good reason to conclude from the writer’s experi-
ments and studies that small knots, swellings, or tufts of roots on
orchard trees have no effect on their growth. Where these knots,
etc., can be removed without serious injury to the tree, it may be
best to remove them. Knots or stem tumors on the outer limbs or
twigs may be removed when they first appear. In cases where there
are small growths, galls, or woolly-knot, on the trunks or roots of
large, valuable trees (Pl. IX, fig. 1), it will not pay to mjure the
trunk of the tree by their removal.

Howard’s experiments, previously cited, prove the futility of
cutting crown-galls from the young apple trees and treating them
with antiseptics. The trees used in his experiments, if they had not
been treated, might be alive and bearing to-day.

Ina pall experiment with seedling trees, the writer cut off the
soft galls from a number of yearling cepillines and planted the seed-

186

i

70 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

lings in a nursery row without further treatment. Of those living at
the end of one year, 14, or 36.8 per cent, recovered; 16, or 42.1 per
cent, developed traces of crown-gall; 3, or 7.9 per cent, developed
large galls; and 5, or 13.2 per cent, developed hairy-root. At the
same time there were planted in an adjacent row a number of the
same lot of seedlings with both hard and soft galls remaining attached.
During one season’s growth 12, or 37.5 per cent, made no further
development; 15, or 46.9 per cent, Increased in size in pace with the
growth of the tree; and 5, or 15.6 per cent, developed hairy-root
from their surface. All that hved made a good growth. Of the first
lot 25 per cent died, presumably nearly all from wounds, and of the
second lot only 3 per cent died.

In planting an orchard it is better to plant healthy trees and take
no risk of diseased trees recovering, since only about one-third of
the trees diseased with crown-gall, as shown by experiments, fully
recover. The initial cost of the orchard is only a small portion of
the total cost of mamtenance, and in general it pays to plant the
best rather than to plant and attempt to cure diseased trees.

SUMMARY.

The disease or diseases of apple trees manifested by the forms or
types known as crown-gall and hairy-root occur in nurseries and
orchards in the United States wherever apple trees are grown. They
have been reported in one or more forms from Europe, South Africa,
New Zealand, and Australia.

The crown-gall type of the disease occurs on apple trees in two
forms; the soft and the hard. The former differs slightly from the
latter, especially in its more rapid growth, softer texture, and less
permanent nature. Apple crown-gall in both forms is related to the
crown-gall of the almond, apricot, blackberry, cherry, chestnut,
grape, peach, pear, plum, prune, raspberry, rose, and walnut.

The hairy-root type of the disease is of four forms: The simple
form, characterized by numerous roots springing at right angles
from a larger or main root; the woolly-knot form, characterized by
numerous more or less parallel roots springing from a hard gall or
swelling on a longer root; broom-root, a side root which is much
fasciated with fine branch roots, often negatively geotropic; and aerial
tumors, or knots, which are the woolly-knot form on the limbs of the
trees. All of these forms of hairy-root are probably directly related
to the forms of crown-gall, but for convenience and clearness they
are discussed and treated separately.

The soft form of crown-gall is most common on yearling apple
seedlings, though usually not abundant. It is occasionally found on
budded and root-grafted trees. The hard form is common on budded

186

SUMMARY. 71

and much more abundant on root-grafted trees. Hairy-root of the
simple form is frequent on apple seedlings and on budded and root-
grafted trees. The woolly-knot form of hairy-root is the most
common form of the disease, especially on 3-year-old root-grafted
trees in the nursery and on orchard trees. The broom-root form
occurs occasionally on trees grown on loose soils.

Crown-gall of both forms develops chiefly the first year on seed-
lings and root-grafted trees in the nursery. It gains entrance almost
entirely through wounds. On root-grafted trees it occurs most com-
monly on the lower end of the scion at the union. In the experiments
less crown-gall was found on nursery trees the second and third years
than the first, which is strong evidence that it ceases to develop to
any great extent. Hairy-root develops on root-grafted trees to some
extent the first two years, and to a less extent the third.

In the experiments varying the depth of planting the union had
little effect on increasing or decreasing the amount of disease present
in apple trees grown from root grafts, but a better stand of trees was
obtained by the shallower planting of the union. Very little difference
was shown in the amount of disease resulting from the use of the
upper half and the lower half of seedling roots for making root grafts.

An increase of both crown-gall and hairy-root occurred in root-
orafted trees when apparently healthy scions or roots were taken from
trees otherwise diseased. The use for making root grafts of roots
from apple seedlings diseased with the simple form of hairy-root
resulted in an increased stand of trees in the nursery, but also in a
large percentage of inferior trees diseased with hairy-root of the simple
form. The disease did not as a rule extend from the root to the scion
portion of the tree during the three years of growth in the experiment.
Cuttings from seedlings diseased with this form of hairy-root usually
sent out roots more readily than healthy cuttings and often developed
into vigorous-growing trees.

Where scions for root grafts were taken from yearling trees and
from bearing trees in the orchard, no great difference in the number
of healthy trees obtained from either was noted, but there was a slight
increase of disease in the trees from the scions taken from yearling
stock,

Leaving a bud near the lower tip of the scion did not increase the
disease in trees grown from root grafts. No great difference in the
amount of disease present in trees from root grafts was noted where
seedlings grown from both French and American seed were used.
The results, however, were decidedly in favor of stock grown from
American seed, since the stand of trees with the latter was 25 per cent
better.

186

(2 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

No essential difference was noted in trees grown from root grafts
made from healthy seedling trees taken from a locality where nursery
stock had been grown for many years as compared with those taken
from a new locality where stock had not been grown previously.

Heavy, stiff, clayey, wet soils apparently increase the amount of
disease, especially of crown-gall, in nursery stock. Some lighter soils
show an increase of hairy-root.

In nursery experiments the amount of crown-gall present after the
first year decreased considerably from year to year, while hairy-root
increased slightly, especially during the first two years. In the
orchard experiments the amount and intensity of the forms of the
disease decreased instead of increasing, indicating that older apple
trees In many cases successfully resist both hairy-root and crown-gall
and that many may recover completely.

Crown-gall and hairy-root affected nursery trees in the experiments,
stunting them very slightly and causing them to be only 90 to 94 per
cent as large as healthy trees. In the experimental orchards the
apparent effect on the growth of trees was even less—in fact, hardly
perceptible. These experiments prove that the effect of crown-gall
and hairy-root upon apple trees in the orchard has been overrated,
at least in the established apple districts of the Contra) and Eastern
States.

A marked difference in the susceptibility of varieties of apple trees
to crown-gall and hairy-root has beennoted. Trees of some varieties,
when grown from rootgrafts, tend to develop a large amount of crown-
gall; others of hairy-root, in both cases chiefly on the scion portion of
root-grafted trees. In these experiments, the Wealthy, the Yellow
Transparent, and the Wolf River were the varieties most diseased
with crown-gall; and the Ben Davis, the Wolf River, and the North-
ern Spy were most diseased with See sere |

The period when most apple root grafts become diseased with
crown-gall is apparently the time when the wounds in the union are
being healed by the formation of callus. If the disease could be kept
out during this period it is quite probable that little would occur on
nursery stock except as it gained entrance later through wounds made
in cultivation.

In the experiments, with the fitting of root grafts, where poorly
fitted, especially if the lower end of the scion projected, an increase
of both crown-gall and hairy-root occurred. The disease apparently
did not spread from tree to tree in the nursery rows in the experiments,
since there was little or no increase of disease after the first year.

Little of the crown-gall occurring in root-grafted trees can with
certainty be accredited to the fact that grafting knives as a tule are
not sterilized.

186

eS
1

RECOMMENDATIONS. 7033

Root grafts should be carefully fitted, especially with respect to the
lower end of the scion, which should have a sharp end rather than a
blunt one. The wrapping used should cover the union completely
and should firmly hold the parts together until the graft is planted in
the soil; then it should rot away when growth begins.

In a large number of wrapping experiments cloth wrapping gave
the best results. In a later experiment good results were obtained
with a continuous-thread wrapping applied by a machine evenly and
closely over all the union.

Sand was found to be the best material tested for packing and stor-
ing root grafts. Cold storage is best for root grafts that must be kept
for some time before planting, since 1t prevents the overdevelopment
of callus, a condition which favors the entrance of disease.

RECOMMENDATIONS.

The crown-gall and hairy-root of apple trees is primarily a nursery
disease, gaining entrance most frequently the first year. In a well-
regulated nursery it is desirable to grow and sell the best trees that
can be obtained and at the same time not increase the cost of produc-
tion. With this in view the following recommendations are made:

(1) In order to keep the nursery as free as possible from the disease
all diseased trees should be left in the field at the time of digging and
burned as soon as dry.

(2) The nurseryman should, as far as possible, get scions from
healthy trees by growing them under careful selection or purchasing
them from others who do this. Never plant diseased trees in the
scion orchard.

(3) Buy the best grades of healthy seedlings for budding and root
grafting. Insist that growers of apple seedlings cull out and burn all
diseased ones at the time of digging.

(4) Make close-fitting root grafts, avoiding blunt ends of the root
and scion in the union. Wrap with unwaxed cloth or continuous-
thread wrapping, covering completely and firmly the wounded edges
in the union. The root and scion should be approximately of the
same diameter.

(5) Store root grafts preferably in sand. If the period of planting
is delayed beyond two weeks they should be placed in cold storage at
a temperature a few degrees above the freezing point.

(6) Plant the union of root grafts about 3 to 4 inches below the sur-
face of the ground. Be careful not to break the callus in planting and
avoid wounding the young plants in cultivation.

(7) Propagate by budding, as far as possible, the few varieties
most susceptible to crown-gall and hairy-root. Among these are the

186

74 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE,

Wealthy, the Yellow Transparent, the Wolf River, the Ben Davis, and
the Northern Spy.

(8) Avoid heavy, wet soils, since they favor an increase of disease.

(9) Growers of seedlings should avoid wounding the young trees
with the hoe or other implements of cultivation.

That these precautions will decrease the disease is certain, as shown
by the results of experiments, and an increased profit will result from
their use. For example, wrapping with a close, tight, cloth covering
decreased the percentage of diseased trees 12.9 per cent and resulted
in an increase of stand amounting to 23.9 per cent of the original root
grafts planted. This, based on 15,000 grafts to the acre, is a saving
of $214.80 per acre. The continuous wrapping of root grafts with
thread is more easily and cheaply done and promises to give equally
as good results.

The orchardist is advised to plant the healthiest trees obtainable,
since the initial cost of the orchard is only a small part of the final
outlay. If a tree becomes diseased during the first three or four
years so that its growth is hindered, dig it up and plant a healthy tree
inits place. If trees in an older orchard are diseased, but still bearing
profitable crops, allow them to remain in the orchard, unless there is
danger of infecting more profitable plats of raspberries, grapes, or
peaches. In such case they should be removed, since crown-gall
from the apple tree may infect these plants.

If the growing of nursery stock were confined to apple trees, nursery
inspection for crown-gall would hardly be necessary. Since the dis-
ease attacks and kills grapevines, raspberries, and probably peach
trees, and since it may be communicated to them from apple trees, it
is clearly the duty of a nursery inspector to insist that apple trees dis-

-eased with crown-gall shall not be sold. It is best to include in the

same category apple trees diseased with hairy-root.

On the other hand, an inspector should be certain that apple trees
are diseased with crown-gall or hairy-root before condemning them.
Warts and pimples are not necessarily crown-gall, nor are fibrous
roots certainly hairy-root. The tendency to form fibrous roots
exists under certain soil conditions (PI. ITI, fig. 4). In some local-
ities and under certain soil conditions healthy trees with much-
branched, fibrous roots are grown. These roots are to be distin-
guished from hairy-root formation, which is characterized at the begin-
ning by clustered, fleshy, often fasciated roots, which later become
fibrous through shrinking. Only plainly diseased trees should be
rejected; other trees in the bundle should not be condemned on
account of the presence of a diseased tree, but as a matter of precau-
tion should be dipped in a weak solution of some antiseptic, as one-
tenth of 1 per cent of corrosive sublimate, for five minutes and washed
in water before planting.

186

JS IEE ON IDI

7d

00 hie Ah ames Ne at A at shel =e? ibe SEY

METHODS AND CONDITIONS OF EXPERIMENTATION IN THE STUDY
OF CROWN-GALL AND HAIRY-ROOT.

In order to prevent useless repetition, a brief description will be
given of the methods and conditions under which each set of experi-
ments was performed, the results of which are given in previous
chapters and in the tables in the following portion of the appendix.

EXPERIMENTS IN THE GREENHOUSE.

All greenhouse experiments were conducted at the Mississippi
Valley laboratory, St. Louis, Mo. Seedlings of various kinds of
shrubs and trees were grown in pots and benches, as follows: All soil
and pots were sterilized for three hours in an autoclave at a tempera-
ture of 239° F. The benches were constructed of new pine and cypress
lumber. Before filling the benches with soil they were washed with
a strong solution of Bordeaux mixture. All seeds before planting
were sterilized in one of two ways—either in concentrate sulphuric
acid for ten minutes or for an equal time in a one-fifth of 1 per cent
solution of mercuric chlorid, followed in either case by repeated
washings in sterile water. In these experiments 6,176 plants were
erown and ‘used in five years.

EXPERIMENTS IN THE NURSERY.

The experiments in nurseries were extensive and included the plant-
ing of 143,763 apple seedlings and root grafts of 256 varieties during
a period of six years. They were of two kinds, independent and
cooperative. In each experiment all seedlings, cuttings, or scions
were selected from the same stock, all root grafts’ were made and
planted equally well in each portion, and all portions of each plat
were of uniform soil and drainage and were cultivated equally well,
all of the work being done by skilled workmen under the direction and
personal supervision of the writer. Many experiments were dupli-
cated in different localities, insuring greater accuracy in results.

Independent nursery experiments.—These were conducted in nursery
plats on land owned or leased by the Department and cultivated by
its employees. There were three plats of the following description:

Independent plat 1 was located near Louisiana, Mo., on a slightly
sloping piece of upland consisting of a heavy, colluvial clay loam. It
was situated so that it did not receive the overflow from adjacent

a In all experiments where the term ‘‘root graft” is used, unless otherwise specified,
reference is made to the form of root graft known as whip or tongue gralt.
186 77

78 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

fields. It had been planted to field crops for twenty years and had
a clover crop when taken for the purposes of experiment. In the
experiment on this plat 19,700 root grafts and trees were grown
during 1903 and 1904 on 4 acres of land.

Independent plat 2 consisted of about one-half acre of level land
on the Potomac Flats, south of Washington, D. C. It consisted of
an alluvial loam, the soil having been formerly pumped by dredgers
from the bottom of the Potomac River. In this plat 6,400 root
orafts and seedling trees were planted in 1907.

Independent plat 3 consisted of about one-half acre of gently sloping
clay loam on the Arlington Experimental Farm, in Virginia, south-
west of Washington, D.C. In this plat 6,043 root grafts were planted
in 1908.

Cooperative nursery expervments——Experiments were conducted
during the years 1905 to 1908 in cooperation with six of the largest
nurseries in the Mississippi Valley. Eight experimental plats, of
about 1 acre each, were planted in as many different localities in five
States. <A total of 113,620 seedlings and root grafts was planted.
A description of the plats follows:

Cooperative plat 1 was located in southwestern Iowa on level valley
land consisting of a colluvial clay loam. The previous crops for five
years were grain. :

Cooperative plat 2 was located in southwestern Iowa on sloping
upland consisting of a light clay loam. The previous crops for five
years were oats one year, corn one year, and plum trees three years.

Cooperative plat 3 was located in southeastern Nebraska on level
upland consisting of a loess loam. The previous crops for five years
were corn one year and cherry trees four years.

Cooperative plat 4 was located in western Illinois on level upland
of heavy black loam mixed with clay. The previous crops for five
years were grain.

Cooperative plat 5 was located on level valley land in eastern
Missouri consisting of a colluvial loam mixed with some sand. The
previous crops for five years were cowpeas one year and peaches four
years.

Cooperative plat 6 was located in eastern Kansas on level valley
land consisting of an alluvial sandy loam. The previous crops for
five years were corn one year, osage ) orange one year, Kafir corn one
year, and apples two years.

Cooperative plat 7 was located in eastern Missouri on level valley
land consisting of a colluvial clay loam. The previous crops for five
years were cowpeas one year and peaches four years.

Cooperative plat 8 was located in northwestern Arkansas on level
valley land consisting of a sandy loam. The previous crops for five
years were grain.

186

|
|
'

METHODS AND CONDITIONS OF EXPERIMENTATION. 79
EXPERIMENTS IN ORCHARDS.

Four orchards were planted with both healthy and diseased apple
trees. These were situated on land owned or leased by the Depart-
ment. They were located and designated as follows:

Orchard 1 was located near Louisiana, Mo., on a gently sloping
_ piece of upland consisting of a heavy clay loam. The land had been
planted to grain and clover for twenty years. This orchard was
planted to 208 apple trees.

Orchard 2 was located on the same block of land as orchard 1,
but it was lower and wetter in rainy seasons. It contained 261 apple
trees.

Orchard 3 was also located on the same block of land as orchard 1,
but followed the trees grown in independent plat 1. It contained
1,108 apple trees.

Orchard 4 was first planted on the Potomac Flats, south of
Washington, D. C., on built-up land from dredging, similar to that
in independent plat 3. The 500 apple trees in this orchard after
one year were transplanted to a block of land with a colluvial- clay
loam on the Arlington Experimental Farm, in Virginia, where they
are now located.

The trees for planting in these orchards were selected as follows:
Healthy, vigorous, 2-year-old apple trees with a well-balanced root
system of smooth roots (PI. III, fig. 3) were selected in each experi-
ment for a check or control. To test the effects of the forms of
disease there were selected sets of trees of the same varieties, of
equal size, and from the same stock of trees, some of which were
diseased with crown-gall (Pl. I, fig. 1) and others with hairy-root
(Pl. I, fig. 2). All of the trees used in the experiments were selected
by the writer. Both healthy and diseased trees were planted and
tended equally well.

All of the data on these orchard and nursery experiments were
personally recorded by the writer, notes being taken on each indi-
vidual tree.

186

80 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

TABLES GIVING THE RESULTS OF EXPERIMENTS IN THE STUDY
OF CROWN-GALL AND HAIRY-ROOT. 4

TABLE |[.—Development of crown-gall and hairy-root on transplanted seedlings in the

NUIsery.
Ageof | Number of| Seedlings, | Seedlings,
seedlings. | seedlings. galled. hairy.
Years. Per cent. Per cent.
1 350 0.6 3.1
2 116 1.4 ib bey/
3 114 1.5 9.4

TaBLe II.—Comparative development of crown-gall on grafted and budded trees in the

nursery.
|
Grafted trees. Budded trees. Decrease
Variety. Year |S data
Smooth. | Galled. | Smooth. | Galled. | _ trees.

: Per cent. | Per cent. | Per cent. | Per cent. | Per cent.
BeneDaviSeeec. cence ercce ie a nee ee 1904 78 22 91 13
On aos eae 5 oe on Re eee ee 1905 60 40 92 8 32
BlacksAMNEGle se ee ee A eee 1904 89 11 99 iL 10
PIMOS. 325 Soo sae ean ee eee etter 1905 70 30 99 1 29
Olden bute. 2. bias. sokee = Soe sees eee 1904 83 17 96 4 13
ORS eee ee wer ee See ee eee 1904 89 11 99 1 10
Wieal this See ean ane See eee 1904 54 46 93 if 39
Ce et eae ry Ne aa Te Gare nea eae are 1904 83 17 97 3 14
1D ea eee ee ees eras 6 Sep ie 1904 88 12 98 2 10
Wellowsiransparentesece --- sees ee 1904 94 6 99 1 5
Oe Oats Soe ert ane eee 1904 89 11 92 8 3

The data in Table II are given from a number of localities in the
Mississippi Valley, Virginia, and North Carolina.. The names of the
nurseries are withheld because the reports were confidential. At
the time the reports were received, most nurserymen designated as
“crown-gall” all forms of crown-gall and hairy-root, and in the
table they are combined under the term “galled.”

TABLE II].—Results on the health of trees of varying the depth of the union in planting
: root grafts.

Trees with long scions. | Trees with short scions.
Year.
Number. | Diseased.6 | Number. | Diseased.®
Per cent. Per cent.
TA OF gs ee ik ee a Or a ee 754 13352 769 13E5
1LQOB e oih5 Ss SC ia eo ys eae 980 35.0 870 48.4
Total Ses Ee ea as oh Oe Sn eR en eden 1,734 25.5 1, 639 32.0°

a In these tables both forms of crown-gall are included under the term ‘“‘ galled,”’ and all of the forms
of hairy-root under the term “‘hairy,’’ unless otherwise specified. The word ‘‘smooth”’ is used to
designate trees free from the disease.

6 In this table the term ‘‘diseased”’ includes ‘‘galled”’ and ‘‘hairy”’ trees.

186

RESULTS OF EXPERIMENTS.

‘

81

Taste IV.—Results on the health of trees of varying the depth of the union in planting
root grafts, second experiment.

Year.

Number.| Galled.
Per cent.

1, 288 21.3

2, 450 6.6
1,079 mt
4,817 9.4

Trees with long scions.

Hairy.

Per cent.

7.6
10.6
8.6

7.5

Trees with short scions.

Number.

1,446
2, 960
1,182

| 5, 588

Galled.

20.9
5.3
1.6

8.6

Per cent.

Hairy.

Per cent.

TaBLeE V.—Results on the health of trees of selecting upper and lower piece roots for root

Year.

grafts.
Trees from grafts on upper
piece root.

anes Galled. | Hairy.
Per cent. | Per cent.
743 19.8 Cod,
1, 675 6.0 itt yl
580 1.9 10.9
2, 998 8.6 1209

Trees from grafts on lower

Number
dug.

703
1, 285
602

2, 590

piece root

Galled.

Per cent.
22.0

4.5

ea

8.5

Hairy.”

Per cent.
7.4

10.6

tao

9.0

TaBLE VI.—Results on the health of trees of using seedlings diseased with hairy-root in
root grafting, first series of experiments.

Year.

Trees with hairy-root grafts.

Number. | Galled.
Per cent.

1,132 eS
1,922 4.8
922 7.4
3,976 Uls83

Hairy.

Per cent.
73.8
79.2

Trees with smooth-root grafts.

Number.

751
1,481
632

2, 864

Galled.

Per cent.
4.

8.7
Uoll

12.6

Hairy.

Per cent.
7.9

11.0
10.9

10.2

TaBLE VII.—Results on the health of trees of using seedlings diseased with hairy-root in
making root grafts, second series of experiments.

Year.

00414°—Bul. 186—10——6

Trees with hairy-root grafts.

Number. | Galled.

Per cent.

141 1.4
268 Dee,
81 6.2
490 2.6

Hairy.

Per cent.

Trees with smooth-root grafts.

Number.

125
245
99

469

Galled.

Per cent.

Hairy.

Per cent.
5.6

10.6

9.1

8.9

82

THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE,

TABLE VIII.—Results on the health of trees of using seedlings diseased with crown-gall
in making root grafts.

Trees with smooth-root grafts.

Year.
Number.
CRS Gece eos ee eee 125
SOCON Gud 25 2A. See Se ene ene ana eee 245
dD ah To etmek pea Sane ea Ne Maes re Pes ST ee 99
TOtal ie Sen EE ace ae een aie: 469

Galled.

Per cent.

18.4

3.7 |
2.0 |

7.3 |

Trees with galled-root grafts.

| Hairy.

| Per cent.

Number.

118
165
107

390

Galled.

Per cent.
27.1
20.1
13.1

20. 2

Hairy.

Per cent.
10.2

NST
5.6

TaBLE 1X.—Comparison of the results on the health of trees from the use of scions from
young and old trees in making root grafts.

|
_ Trees with scions from young _‘ Trees with scions from old

trees. trees.
Year.
| psi | Galled. Hairy. | ee Galled. | Hairy.
| | |

| Per cent. | Per cent. Per cent. | Per cent.
KURT H aw, Suomen eA. ST 2 22h EATS 6.1 215 he! 10.7
NGO GASe See See ie En Se ne ee eee Dee aes 297 | 6.1 19.7 382 6.3 SH
TOO Fe se A ee et res ee Ee 207 | 5th) 15.0 193 1.0 10.4
Totallsse a ee ee eee 733 | . 8.0 14.0 790 5.6 10.9

TABLE X.—Comparison of the results on the health of trees of root grafts on seedling roots

grown from French and from American seed.

Trees from French seed.

Year. .
Sates | Galled. | Hairy.
| Per cent. | Per cent.
NODS C6 as SSS eens ce Sere ee 491 46.8 Oe,
DOO Gee Ses ee ek pee Se ere ae 913 | LS y 6.8
SOQ T oaks ose Belk a ee IS TR ys See en ne 398 | D7, (S334
NG GaSe hey eee ee ee 1,802 19.1 5.8

Trees from American seed.

_ Number
| 4 dug.

Galled.

Per cent.

Hairy.

Per cent.

OO ym
is

~]
=

TABLE XI.—Results on the health of trees of using seedlings from localities where nursery

- stock has been grown for many years.

Trees from an old locality.

Year.
Number
dug.
1905s Sas: siete ee 937
VOQG ee eee Sea eee ee Be eter ie a 1,816
19075 Se Sess eee 738
Total ne 2. See ee 3,491

Galled.

Per cent.

Trees from a new locality.

Hairy. meee
Per cent.

3h 5 491

Da 913

4.1 398

4.7 1,802

Galled.

Per cent.

Hairy.

Per cent.
ya |
6.8

7.3
5.8

ae

RESULTS OF EXPERIMENTS.

83

TaBLE XII.—Results on the health of trees of heavy, wet soil compared with drier soil in

the same locality.

Num-

ber of Nature of soil.

plat
lee ese Heaviyenwie jloalml she cs a ee eee: ae ae
Die oer Dan, Cie Opie as cae eee ee ee Aer Sok ae eats

Trees grown.

Number. | Healthy.| Galled.
Per cent. | Per cent.

5,018 75.1 19.4
6,038 75.9 14.1

Hairy.

Per cent.
aD
10.0

TaBLe XIII.—Results on the health of trees of heavy, wet soils compared with dry soils in
different localities.

Nature of soil.

PETC MWe by O AMINE tera estate Slate wfave ofa lais ste )tejavele ainie aiaie he sc vets
(Bosse seeee CL OR ens ee gears a else eumena sabe ce
Miah tel Oessiloamie stars a aaeentine eis ees en aee ee pea ee seeets
Macht sand yaloamises ears eee eee eee - Ge See

Trees grown.
Number. | Healthy. | Diseased.
Per cent. Per cent.
4, 460 76. 6 23.4
4,798 Ute Y 22.1
4,454 86. 0 14.0
4,809 Sieed 12.3

TaBLE XIV.— Maximum development of crown-gall and hairy-root, by years, on grafted
trees.

2h

Trees dug.

Number of set.

First |Second}| Third

Galled. Hairy.

First |Second| Third | First | Second! Third
year. | year. | year year. | year
Per ct. | Per ct. | Per ct. | Per ct. | Per ct.

13.8 TU 6. 2 9.8 | 9.7
10.3 3.6 3.0 6.3 6. 2
4.3 1.8 Wok 9.1 | 8.7
Ral 3.1 2.6 5.3 6.5
8.3 3.6 AL 9.3 9.8
6.2 9 7.4 7.4 Teo
6.8 7.6 les 10. 6 | 10.6
9.1 4.7 bas earston Gameaty

year. | year. | year. | year.
No. No. No. Per ct.
1a = So 8e See oe er eee aaa 3,392 | 3,168 | 3,254 24.5
DN ad SR eo ee a S21 RAE 4S 4a deslG 47.7
Shits See See ene 2,161 | 2,014} 2,077 24.2
(ha 2 Ae a Dae i a 1,078 | 1,003 998 1833
io SSE SOS ey Fee ee 782 745 612 25.3
(Des 5 Oe co SA a a 350 309 321 GS 4
eee eS eee 620 584 567 26.9
Mo tale eee = Me 9,904 | 9,257 | 9,145 26.7 |
|

Total trees in experiment, 28,306.

TaBLE X V.—Average height of healthy and diseased root-grafted trees at the age of one year

Location of plats.

Healthy trees.

Number.

Height. Number.

BAST eEMEIANSAS 2 8e— Stee occ cla cines
WHESTCEMSIITIMOISS. i ee a leccekcces

1, 689
1, 293
1, 936
1, 665
1,300

7,883

Inches.
35.8
36.3
37.0
43.1
30. 5

37.2

Galled trees. Hairy-rooted trees.
Height. | Number.) Height.

Inches Inches.
724 32. 4 265 32.8
759 B87 169 33.2
653 S81 287 | 34.0
578 42.4 386 39.9
889 28.8 246 | 26.6
3, 603 38. E 1,353 34.0

84

THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

TABLE X VI.—Average height of healthy and diseased root-grafted trees at the age of two years.

Healthy trees. Galled trees. Hairy-rooted trees.
Location of plats.

Number.| Height. | Number.| Height. | Number.| Height.

Inches. Inches. Inches.
Southwestern TLOWa: sese— see eee 1,902 50.7 302 47.7 411 | 45.3
DONE Cae ase Sa een ee eee 1, 444 63.6 267 57.6 327 56.9
Southeastern Nebraska................-.-- 2,146 52.2 324 50.7 417 51.0
aster lansas = se eee oe eee 3, 028 61.6 680 59. 4 842 59.8
Weesterncillinoiss. 32-3 eee 1, 639 | 52.5 246 48.7 270 48.7
Ieee a iar eae a 10,159| 56.4| 1,819 51.3| 2,267 | 53.0

TaBLE XVII.—Average diameter of healthy and diseased trees in orchards 1 and 2.

Healthy trees. Galled trees. Hairy-rooted trees.
Number
Variety. of }
orchard. Average Average Average {
Number. diameter. Number. diameter. Number. diameter.
Inches. Inches. Inches.
YoOrksimperial 22-5 eee 1 16 2.64 4 2.10 8 2.64
Qo Aes See ee ae eas 2 47 PTE 8 2.39 22 2.51
EEE ———————EEE EEE eee }
ING Gaal See sire rae ee ae | eee ee 63 2.74 12 2.29 30 2. 55
Liye as 078 Bee eM ee APRS Poa 1 16 2. 48 | 2 2. 42 10 2.16
OD ee seer ee eee eee cee 2 23 2.36 9 2.04 10 2. 42
NG beads telesales 39 2. 42 11 2.10 20 | 2.29 )
: |
GAO ee te ee 1 44 2.26 11 2.39 22 | FDR |
1 DS SaaS a ere we yee eee 2 16 2.16 | 13 1.88 18 | Dane
TOL 2h Nain tse Sea eee 60 2.23 | 24 2.10 40 2.23 )
(Gling) sire st crea eae 1 39| 2.23 4| 2.67 14 2. 48
Oe ee eee | 2 25 | 2.23 23 2.00 12 | 2. 23
Do tale sees as ue a pate. 64 2.23 27 2.10 | 26 | 2. 36
Total for all varieties......|...------- 226| 2.42 | (2) ais 116 2.36

TaBLE XVIII.—Number of healthy trees planted of each variety and the number dying
in orchards 1 and 2.

York Imperial
trees.

Ingram trees.

Gano trees.

Collins trees.

Total.

Number of orchard.

Planted. Died. Planted.) Died.) Planted | Died.| Planted.| Died.) Planted.) Died.

| {cae we
eof ati es aes 16: ne 3 16| 2 4g| 3 32| 2 112} 10
DER OP. ees ac, Boone ald 45| 5 230 (anes 27 3 27 0 122 13
Motalea a eee Gilles Ba) || 75 6 59| 2] 9284 23

|
ee

fom

RESULTS OF EXPERIMENTS.

85

TaBLE XIX.—WNumber of diseased trees planted of each variety and the number dying in

orchards 1 and 2.
SOR LUIpeHa Ingram trees. Gano trees. | Collins trees. Total.
Number of orchard.
Planted.| Died.| Planted.) Died.) Planted.) Died.) Planted.) Died.| Planted.| Died.
1G BONERS hate ae oe eeeee 16 1 16 2 32 0 32 5 96 8
SG oe SES wine 45 8 | 31 7 27 4 36 3 139 22
otal eee: - 61 9 | 47 9 59 4 68 8 235 30
| 1
TaBLE XX.—Numober of trees dying in orchard 3 during two years’ growth.
Trees
Condition of roots. pienied Trees dead in 1907. | Trees dead in 1908. | Trees alive in 1908.
in 1907.
Number. | Number. | Per cent. | Number. | Per cent. | Number. | Per cent.
Heal thie eres teeerer ee ee 572 182 31.8 9 | 1.6 381 66.6
CII ls suas Bee eee ne coe te 177 60 33.9 6 3.4 111 62.7
1B BYTE RAS eects es eng ree 359 69 19.2 21 | 5.9 269 74.9

TaBLE XXI.—Results of experiments showing the susceptibility of different varieties of
apple trees to crown-gall and hairy-root.

Variety.

Wrealthyz=2-— ==:
Yellow Transparent.
Wolf River........--

MamMeuses ease
Oldenburg..........
MUISSOUFIC2 = secne8 2

York Imperial... ..-
Miniden<s e222. 3
GiibineS\: aa aes
Northwestern
Greening.

’ Scott Winter........

Yellow Bellflower. -.
Northern Spy....-.-
Bene a WiSse ens ces
Walbridge.-2......
MAES Se eis

>.

C saad ENGR
rown- ‘ Hairy- : gall and | Number
gall. Variety. root. Variety. hairy- | of trees.
root.
Per cent. Per cent. Per cent.
34.4 || Ben Davis......--. 29.9 || Wolf River......-- 46.4 660
27.1 || Wolf River........ ZENS) |llaWiealthyeecesseeeee 43.3 6, 221
21.1 |{ Northern Spy...-.- ON el PB enkDaviseess-ee= 36.1 2,870
19.1 ELUMESes ee Ce 15.3 |; Yellow Transpar- 34.0 2,114
NS Ill Ces sen sacsoces 12.6 ent.
17.7 || Northwestern 10.5 |) Maiden Blush...... 26.4 1, 698
15.5 Greening Northern Spy..---- 26.0 4,166
15: 15|| {Red Jumes.. 5: 1Ok50 ||P Missouria ss) = os 25.9 5,591
15208 ||Missourigs. 5. 45-2 10.4 || Fameuse..........- 25.8 552
14.8 |} Scott Winter...... O3"i -RedeJune== =e ee DOO 2,152
14.2 amboeeeeen ose. Os3n ll PGanOmaees seer ease 24.3 2, 284
11.9 || Yellow Bellflower. 9.2 || Oldenburg......--. 24.0 1, 883
ALE /iall | WCAG yee S90 Grimeseae aaa 23.7 2,477
sls |aWWiellbrid ge: = 22 =- Soo i Ram bowers see 23.5 1,148
9.9 || York Imperial... - Srcr|| Jonathani-=ssese5- 21.0 1, 668
9.8 || Fameuse..._...-..- Ho WW AWAD. sa Se eso 5e 20. 4 2, 287
8.4 || Maiden Blush..... 7.3 || Northwestern 18.2 3, 963
Cath MN Wibild5655sacose 7.0 Greening.
SHIM so Socs555e 6.9 |} York Imperial... .. 18.1 4,073
7.5 || Yellow Transpar- 659) |e Salomess. --=-——- 18.0 623
7.3 ent. Scott Winterssseeee 16.8 613
6.9 || Oldenburg........ 6:33 | gvbimcler see - 555 asl 16.8 1, 251
632; | Jonathane---o-- = SO) PNG hate Se eee 16.6 1,497
Se2 a |e Marthaec 5 esses. 5.9 || Yellow Bellflower. - 16.5 546
4° 8:||) Wihitney.-- 3. < -- 5SuOnaWial DEG Gems sas ee 14.1 2,328
iBaldiwinteees ses Ae Martha sees 10.7 1, 286

In Table XXI in the first two columns is given the percentage of
trees of 24 varieties diseased with crown-gall, arranged in the order
of their susceptibility, from the highest to the lowest; in the third
and fourth columns is given the percentage of the same varieties dis-
eased with hairy-root, similarly arranged; in the fifth and sixth col-

186

86 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

umns the results of the first four columns are combined; and in the
last column is given the total number of trees of each variety grown
in five years.

TABLE XXII.—Results of experiments showing the variation in susceptibility to disease
of scions from different localities.

VARIETY, WOLF RIVER. EXPERIMENT CONDUCTED IN EASTERN KANSAS.

Num- Trees in experiment.

ber of :

nurs. Location.

ery. Number. | Diseased.) Galled. | Hairy.

SS ee eS Eee | ESS ee

Per cent. | Per cent. | Per cent.
40.2 20.

DA NOW aise Sis Ris sere Sie on neon See eee 244 : 20.1
Sb ae (0 0 aes Seep eee ye e eg en) enim i A. ae a oe 50 38.0 14.0 24.0
QO: MASS Url Se ee eee eee at! ame Dan aoe 250 36. 4 ee 19.2
By (aes (6 V0 eres Aero IAN a ap eee ee ML Lm os aR ATT Agee 189 33.3 14.8 18.5
63/2 C6 Coe een eee Shes teh een Se eRe Se re Ne ee 175 30.8 11.4 19.4
Bh OW Be Fo Se erro eee ce tes Ee 280 30.3 10.7 19.6
5:4] 4 Caltiorniae ate has eae See ee ee nee ieee es ao ee 190 26.8 8.9 17.9
40 Michigan sass sccteam meaner eee Scie ee Saat e 250 26. 4 8.0 18.4
Te) CIOS ase Ses ere a aE Se Ie Sa ue 327 22.9 6.4 1635

121 IMEISS OUT Sa a 5 ae ates nn ped cere op 345 29.6 18.8 10.
USN eRANSAGH 2 SER sre hep itn teen ep ee eet py eee 800 25.0 20.1 4.
i Wea id Wy eee eee es Ob i ee cage A an Se ROR i ea ca 300 23.0 17.6 iy.
LO: (Californias se x Sees Sat ser ap aay ee en 90 2290 16.7 5,
SF | MEISSOUTIE S325 eee SS, a aah es he ees er 200 21.0 13.0 8.
Oca CLO eae ey ERIE GC ares PN Sete I a eee 85 20.0 14.1 5.
| ORIG s ooo eee ee eee te: Se eee eee eine 377 19.4 14.3 De
DENT OW a ea ee ese eee a rae 190 14.2 7.9 6.
4) Michigan Se. oc fact Seco Biss eee nee en ae 315 12.1 8.0 4,
VARIETY, YELLOW TRANSPARENT. EXPERIMENT CONDUCTED IN EASTERN
NEBRASKA.
DOW Bees se ee ee ie a ines eee Ee 309 19.1 2.8 9.1
3h] AMEISSOU TE =o es oe a Se 200 10.0 5.0 5.0
7 Mpa Gc) ou te2) oes eee eR 7 eee eee ok ae le eadas 460 8.7 Sao Dad,
Dy) MO WD oie aie renee hee, ees ge mae ee koe Vga emp ea 190 7.9 3) 4.7
6: | IMISSOUTTS tees 2 ee a ee Senate omer a ee eer 177 Use EY / 5.6
5: | California. eee Sete ea ie eg ee ee 335 6.3 1.8 4.5

TaBLeE XXIII.—Results of experiments showing the comparative communicability of
forms of crown-gall and hairy-root.

Seedlings in experiment.

Treatment of seedlings.
Number. Galled. |- Hairy.

Per cent. Per cent.
1, Control Cut). <5 int Rene ee ef ee Eee 1,44 0.8 6.6
2-Controlchipiinserted as. seer or. eee eee ee eee 1,426 ile Uh 8.4
3, Piece ‘ot:soft gallinserted 22 Sener ne ee ee ee eee 1, 382 8.7 1.2
4-Pieceof hardigallinserted Sages ete ote eee ee 1,324 1.6 6.5
5, Piece from hairy-root seedling inserted......................----- 1,330 3.1 6, 2
186

Re wr Oo © Ore © 00

RESULTS OF EXPERIMENTS.

: 87

TABLE XX1V.—Results from using root grafts inoculated with pieces of apple crown-gall

of the soft form.
| | uni Grafts inocu- | Grafts with
ny a lated with gall | root entp in-
“ Age Number | : chip. serted.
Number of experiment. Wat trecss lnoninocs!
Galled. | Hairy. | Galled.| Hairy. | Galled. | Hairy
Per ct. | Per ct. | Per ct. | | | Per ct. | Per ct.| Per ct.
Tie BISE Boon On oan es Ban eee | 1 year-..-| 1,600 25. 3 4.1 45. 4 3.6 39.5 2.8
The ee See ote ene eee ee | 2 years..| 1, 445 8.3 9.3 36. 6 6.3 10.6 8.3
ie es et Sos. .| 3. ¥ears<- 1,378 3. 6 9.4 19. 5 | 7. 6 | 4.6 10. 4
eee See ee | ee | |
| 4,423] 108 Tb len S422 5.8 | 18.9 7a
Quest a 1 year... Geao Ware! PEK iai | 63a 0 | lo: taciae me reT
Vika AS Sm a ae er a | 2 years... 661 14.7 12.9 35. 7 20. 5 16.5 1G
25 10. 4 12.1 36.5 | 19.2 HGS 7 16.0
ae en Eat Sb da ee 1,586 8.0 81] 22.6 88] 10.7 10.7
TILER es ce i ea raed a eee Telos et ES: lee S85 | OT. A 85} 165 9.0
TaBLE XXV.—Results of experiments showing the increase in the communicability of dis-
ease due to defective root grafting.
| | Trees with grafts well made. | Trees with grafts poorly made.
Number of experiment. - | ee | ,
< |Number.| Galled. Hairy. | Number.| Galled. | Hairy.
| pe
earl
Per cent. | Per cent. Per cent. | Per cent.
Thien Sacks Ie a Se eaten ee 1 year.....| 1,078 13.3 2.6 869 55. 0 3.1
i LP Sess sy toe cles ites ees esc eee coe ee 2 years....| 898 5eal! 5.3 771 15. 3 7.4
1 a = A ee 3 years 998 oe L 6.5 789 4.3 10.3
| 2,974 7.6 5.0| 2,429| 25.9 6.8
oS Sin. eg a ete ga | 1 year..... 268| 11.6 Ane 247| 51.5 1.6
gee con! ROSE ee ee eee 2 years 447 7.4 9.2 401 | 16.5 16.2
715 8.8 7.3 | 648 | 29.8 10.7
2 nS Hee eee 2years....| 1,283 6. 7.9 1, 035 | 19.9 11.9
Titia is 2a Seared teen | 4,972 7.9 | 5.9] 4,112 | 25.0 8.8
1 {

TaBLE XXVI.—Results of experiments with scions taken from trees diseased with crown-

gall and with scions from healthy trees.

(Experiment 1.)

Variety.

GE a ae 2 Se a
ve epee SSS BOS a6 See

PRO DAP cs te ee SEE

| Number obtained from scions
from healthy trees.

| Number obtained from scions
from diseased trees.

| Smooth. | Galled. | Hairy.
122 | 71 52
29 | 56 21
112 | 24 8
107 | 30 33
207 | 36 | 25
577 217 139
| 61.8 23.3 14.9

186

Smooth.} Galled. | Hairy.
|

105 53 | 107
| 19 75 10
99 36 18
77 16 33
191 58 | 38
| | 491 | 938 | 206
52.5 25.5 | 22.0

88 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

TABLE XXVII.—Results from experiments with scions taken from trees diseased with
crown-gall and with scions from healthy trees. (Experiment 2.)

Number obtained from scions | Number obtained from scions
from healthy trees. from diseased trees.
Variety.
Smooth. | Galled. | Hairy. | Smooth.| Galled. | Hairy.
Guri0 2305) 2 ee ee ee ee | 236 3 44 200 16 30
Wealthy. 2.040 oe See oe ee 281 93 440 388 169 61
WOE BUI veri: 92ce oe see ee ene ences 87 2 12 104 14 30
Obal. 35555 Soo a ene eee ae 604 98 100 | 692 199 121
Percentage for all three varieties ........-. 75. 3 | 12.2 | 12. 5 | 68. 4 19. 6 12.0

TasBLeE XXVIII.—Results from experiments with scions taken from trees diseased with
hairy-root and with scions from healthy trees. (Experiment 2.)

Number obtained from scions | Number obtained from scions

from healthy trees. from diseased trees.
Variety.
[ | |
Smooth. | Galled. | Hairy. | Smooth.| Galled. | Hairy.
INOFtHerniS DYi= 2 226 ee eee ee 70 0) 13 68 3 11
Gang: 28 22 aha ke ene Soe eee 236 3 | Ae 180 7 50
RVVOLE ECT V Crea acer eiereee ee ee 87 2 | 12 140 2 | 25
Charlamoiin s240-- ek eee se eee eee 87 2 12 30 it 7
Potaleto cm. ty. ceek. ere eee & 480 7 81 418 13 | 156
Percentage for all four varieties..........-- 84.5 1B 14.3 VARY 2.2 | 26. 6

TaBLE XXIX.—Results from experiments with scions taken from trees diseased with
crown-gall and with scions from healthy trees. (Experiment 3.)

Number obtained fromscions | Number obtained from scions
from healthy trees. from diseased trees.
Variety.
| [

Smooth. Galled. | Hairy. | Smooth. | Galled. | Hairy.
WioliRtiverss Sa. eee eet eee 46 20 14 38 | 6 12
Ganosts ree. 8 Fe ee 65 4 35 43 0 23
Wealthy 5:25. 6.222 sos ee 93 83 11 127 153 38
Total® (2 34-2 ea ee eye 204 | 107 60 | 208 | 159 73
Percentage for all three varieties.......... 54.9 | 28.9 16.2 47.3. 36.1 16.6

Taste XXX.—Results from experiments with scions taken from trees diseased with hairy-
root and with scions from healthy trees. (Experiment 3.)

Number obtained from | Number obtained from
scions from healthy trees. | scions from diseased trees.
Variety.
l
Sao Galled. | Hairy. Smooth. Galled. Hairy.
|
eS
Wolf River... sok oA ee ee 46 20 | 14 44 | 20 35
Gans hse. eee ee eee 65 4 | 35 47 10 38
Wealthy 3 2cc5 5) (Re ae es emma 93 83 | 11 | 37 | 16 | S
iNerbhermiSpye:_ =). 3220 6 2) eee 16a 6 ive) 13 | 0 3
@hatlawigt 37252. t. es oe eee 14 O7 7 2A | 1 | 34
Gtal 5.0: oc ee eee 234 | 113° 84 165 47 118
Percentage for all five varieties ........... 54.3 26. 2 | 19.5 | 50. 0 14.2 35. 8
|

186°

RESULTS OF EXPERIMENTS. 89

TABLE XXXI.—Results from experiments showing the decrease of disease among trees
in nursery rows during the second and third years. (Experimental set 1.)

|

Diseased trees, Diseased trees, Diseased trees,
Number of first year. second year. third year.
Number of experiment. trees in ex-
periment.
Galled. | Hairy. | Galled. | Hairy. | Galled. | Hairy.
Per cent. | Per cent. | Per cent. | Per cent. | Per cent. | Per cent.
i estesede onGeocaae Seneca 9,814 24.5 6. 2 13.8 9.8 ; 9.7
WS SE om ae Oe at ee 4,271 47.7 3.0 10.3 6.3 3.6 | 6.2
DAS SeneStae sa tSeaeOl eae 6, 252 24. 2 7.5 4.3 9.1 1.8 | 8.7
LAS AERA te 8 Ss Se ee 3, 079 13.3 2.6 5.1 5.3 B35 ily 6.5
in SC Sci ac Saas ea oe eee 2,139 29.3 4.1 8.3 9.3 3.6 | 9.8
2 22 So se dn See ok eee 980 15.7 7.4 6. 2 7.4 9 inl
Uist GOS Ene een 1,671 26.9 7.3 6. 8 | 10.6 7.6 | 10.6
Oo Galena ese 28, 206 26.7 5.5 9.1 | 8.6 4.7 8.7

TABLE XXXII.—Results from experiments showing the decrease of disease among trees
im nursery rows the second year. (Hxperimental set 2.)

Diseased trees, | Diseased trees,
Number of first year. | second year.
Number of experiment. trees in ex-
periment. |
Galled. | Hairy. | Galled. | Hairy.
|
Per cent. | Per cent. | Per cent. | Per cent.
Ihe Wao ASO EASE COMBS EHS SSO ACA Ie earner Sere 2, 480 22. 6 a0 19.1 13.1
Do Soe Se See SR re TONNE te ee aE 1, 187 24.7 6.0 12.0 10.5
a ks oy Soe ee Pe Bai oer ip eae at Penn ete eae 133 9.1 7.9 2.8 9.7
gS UAE SEAS S Sa ee Ne en ene eerie ee ne 1,369 30. 7 2.9 SS 12.5
The Sooo ee ee eae ee en eee a em ea 1,105 ia 14.7 20.6 15.4
Cis ty ba GES HEE 5 Be ee Coe eee nna tel Den Mele Debaes aan’ 201 3.4 13.1 3.4 27.3
OSS oR OR DSS ERs BO NC a Re eet ES SPM 379 14.5 ink 4! 14.9 12.1
ANGLIA) Le Sia eee Sn SC Tee SS ee a a rT 8, 454 20. 0 7.9 12.8 10.3

TaBLeE XXXIII.—Results from experiments showing the decrease of disease among trees
in nursery rows the third year. (Experimental set 3.)

| Diseased trees, Diseased trees,
Number of | second year. | third year.
Number of experiment. | trees in ex- | |
= periment.
| Galled. | Hairy. | Galled. | Hairy.
Per cent. | Per cent. | Per cent. | Per cent.
ls Soc Nea aac See Benen ae ees 2, 308 | Tle 7 6.7 : 13.5
Ee ee eta oa wih cee es clogs en's eee 556 | 12.5 4.3 1.8 4.7
Ds CSersSre cele. bes Se er 1,005 6. 2 6.8 lel 10.3
4s bee bsne 66> ce ae ee ee ee 446 12.6 5.4 Ont U2
2 3 BS See S Sc SoS TC ON eee 642 20. 6 4.6 1.9 5.6
Os 335 See 6Goge SEs See DORE eee ee 133 9.0 10. 4 .0 3.0
Ue Sector = = Bee eee a a eee eae a ee eg 136 | 14.1 14.1 3.1 13.8
SUG s J SOR ag enn one Sane eee 5, 226 11.7 | 6. 4 | 2.6 | 10.2
186

90 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE,

TABLE XXXIV.—Condition of the roots of the trees in orchards 1 and 2 at the time of

planting.
Number Healthy trees. Gailed trees.

Number of orchard. a ees

anted.
eae Number. | Percent. | Number. | Per cent.
OD ae Se Pine eRe AS Lk a eee fateay UY SOL ay EB Rr 208 112 53.8 96 46. 2
DR oF We UR Here Tse A pear cy asi aes ene Plier fue SES 261 122 46.7 139 53.3
Th Galle etic EGS re een cde Sek eee 469 234 49.9 235 50. 1

TaBLE XXXV.—Condition of the roots of the trees in orchards 1 and 2 after six years’
growth.

Dead trees. Healthy trees. Galled trees. Hairy-rooted trees.
Number of orchard.
Number. | Per cent. | Number.| Per cent.| Number.| Per cent. | Number. | Per cent.

LS GREE Sab eae Gems: 18 8.6 115 55. 3 21 10. 1 54 26. 0

Ue ores Penis laneen th 35 13. 4 IB 42.5 53 20. 3 62 23.8
Rota se 53 11.3 226 48. 2 74 15.8 116 24.7

TABLE XXXVI.—Results from experiments showing the development of disease wpon
healthy trees grown for six years in orchards 1 and 2.

Healthy Condition of trees after six years.

trees et
planted. | ead. Healthy.| Galled. | Hairy.

Number of orchard.

NG a ROR Ses Seca Sa tt gp ici Dargai eS a aT Eo 112 10 83 1 18
Dv TRISBES DS RES AES Z ESSER S area, Cyt ae aie SM siete ip Re ay, wR 122 13 _ 70 10 29

A Yo re eal sees KAD Urea lee cM Rn) tks oe 234 23 153 11 AT
POE COT ee a aN aD oe age 100 9.8 65.4 4.7 20.1

TaBLE XX XVII.—Results of experiments showing the recovery of diseased trees during
six years in orchards 1 and 2.

Condition of trees after six years.
Diseased
trees

planted |) ead: Benen Galled. | Hairy.

Number of orchard.

SPs Sea ee ah ok UAL Sean a niceg Ea 96 8 32 20 36
Sp paisa hd nee ae iy eer eC ae 139 22 4] 43 33

Mo balicscs esti ee ern ieee ER is 235 30 73 63 69
PGTiGe nite chs eis er a eI an ape 100 12.8 ans al 26. 8 29.3

RESULTS OF EXPERIMENTS.

91

TaBLE XXXVIII.—Results of experiments in wrapping root grafts. (Experiment 1.)

Trees 1 year old. Trees 2 years old. Trees 3 years old.
Galled.| Hairy.) NU™- | Ganed.| Hairy. | N¥™- | Galted.| Hair
ae WY-!| ber. p Y-| ber. : y-
Pact IPG. 12 (Bie | IP Be, IDGin || TEai(ain

9.9 2.9 538 7.6 4.3 566 2.6 4.6
8.6 3.9 478 9.2 8.6 523 5.0 9.5
PESO} 3.8 486 LONE &.2 508 6.3 10.0
222 10. 7 486 12.4 11.3 469 Coll 11.3
aul) Usb) 521 19. 8 IIE 520 183 9.8
41.9 9.5 386 14.8 15.8 389 10.5 1633
46.5 6.1 273 29.7 11.3 273 15.0 1235

Kind of wrapping.
Num-
ber.

Clothe ee oes ek 553
1 O10] 0} OXe) Dene ae eee es a eee 546
Waxed paperss-)45---..---/- 525
RPlainkthreadeaee esse eee 504
Waxed thread............... 561
IN@AyARO INR posconcecauaaee 391
WiaixeGsuniOnermrye soe oso. 312

TABLE XXXIX.—Results of experiments in wrapping root grafts.

Kind of wrapping.

Waxed union

TaBLE XL.—Results of experiments in wrapping root grafts.

Kind of wrapping.

Wintxedpanercrssee eee ee ee
TRA Raa {EW SEY Lee rep ee re
Wioxedethneade net ucscceoe sos esco nl eck
IN|@)- Ay Az 0 00 0 Ia i ea

Waxed union

TaBLE XLI.—Results of experiments in wrapping root grafts.

INO Ay) 0) OO eS oo aerauE econo eae

Trees 1 year old.

(Experiment 2.)

Trees 2 years old.
y

Kind of wrapping.

Trees 2 years old.

Number.| Galled. | Hairy. | Number.| Galled. | Hairy.
Per cent. | Per cent. Per cent. | Per cent.
142 9.9 3.5 254 10. 2 5.5
147 10. 2 4.1 239 285 12.1
143 28.7 9.1 238 17.2 12.6
148 18.9 10.8 234 19.7 14.1
Saelie 121 24.8 9.9 253 23. 3 15.0
144 33:3 7.6 245 21.6 1%
eee 65 70. 7 Uo 47 42.6 6.4
(Experiment 3.)
Trees 2 years old. Trees 3 years old.
Number.| Galled. | Hairy. | Number.| Galled. Hairy.
Per cent. | Per cent. Per cent. | Per cent.
201 10. 4 8.0 193 3.6 6.7
168 (eh 4.8 174 he? 9.2
160 11.9 6.3 158 2.5 15.8
173 8.1 10. 4 193 4.1 16.6
185 12.4 6.5 179 4.5 14.0
185 14.6 5.4 174 3.5 18.4
ae 87 21.9 4.6 68 3.0 17.6

(Experiment 4.)

Arkansas plat.

Missouri plat.

Number.
(COUN 6a a ae eS eee ae eres 404
OUD be heerae erie see a ieeece 385
Wid xedspa perk sacri sauem. so2 SS See 374
elaine nneaGee een fe ee 380
Wiaxedsthread'’s ela kaos. wees ewes en eee 359
INGGRYRT AD IE en ame e seins ooo ceie Sore eee 352
VAX OUMUM TOM emennair weyers cic. s ae sveecies cis 175

Galled.

Per cent.

Hairy.

Per cent.

ho
NwWOs
ROTH Re A]

Number.

Galled.

Hairy.

Per cent.
5.6

13.5
14.0
13.7
11.3
19. 4
18.1

186

92 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

TaBLeE XLII.—Combined results for three years of experiments in wrapping root grafts.
(Experiments 1 to 4.)

Trees 1 year old. Trees 2 years old. Trees 3 years old.
Kind of wrapping.

Num- | Galled.| Hairy. | \“%"- | Galled.| Hairy. | NU" | Ganted.) Hairy.

IPS OS IP, Gio IES Gb \ IPs Gi 125 Gin || LPs: Gl
Clothe ase eae acc 705 9.8 4.4} 1,737 7.3 5.9 759 2.9 &, il
Riu bers <3 esr cae seeee 693 8.9 3.9} 1,661 7.6 10.2 697 4.1 9.5
Waxedipaperia ase -o eae 668 26. 0 5.0 | 1,550 9.3 11.0 666 5.4 11.4
IPiainwbhinea dees eee seer 652 21.5 10.7 | 1,566 9.6 14.9 672 6.6 12.6
Wiaxeduthned des se-erascae sce 682 30.3 8.0 | 1,662 14.6 13 705 9.5 11.6
NOswiappineee-=-s.sseo eee 535 39.6 9.0 | 1,504 12.4 16.5 563 8.4 1329
Wiaxe daumionees see sse ee eae 379 48.8 6.6 938 21.5 14.1 341 12.6 13.5

TaBLeE XLIITI.—Final summary of results of experiments 1 to 4 in wrapping root

grafts.
Kind of wrappin Healthy | Galled Ped
J) ee trees. trees. Tee q
rees.
Number. | Per cent. | Per cent.
Cloth 22255: acscicsies Shears Hae SS oe Qo See BEE CORR ORG EAE SEO eE ER Ee rE 2, 814 6.8 5.3
1 240] 0) 0X) eeeeeee ee ee eNe iene Geren NUS Ce eyes Re ie Ee oe as ube os ea oO 2,001 doll 8.6
Wiese di papensan sis. 5 sect rel pe LOU yr oT See eels Oa Rp te on cee ee es 2, 251 12.3 9.7 |
iWaxe dithrend taste sees pe Sha rs cen weap NG hoa CES de ee ea 2,178 16.9 ils |
Plain Ghread sec. & Site es Sh a ge ee ea Re ia eee er nee ee 2,168 SG 13.4
INVA A 12110) OVDON SA Rane ier ne ene wee ree os Ma a id eye eae easeaee 1,784 17.2 14.3
WV COMER C Cait eens aren tee oe Se yet pe eRe cea ae Ss ee 1,025 26.0 1D
A IO) 2h aie erie re Eee pe Fae he yaa etn Bat es Geta ied Maka g oat 14,791

TaBLeE XLIV.—Results of experiments in washing apple scions and roots in a 2 per cent
copper-sulphate solution.

Trees grown from untreated | Trees grown from stock treated
stock. with copper sulphate.
Variety.

Smooth. | Galled. | Hairy. | Smooth.| Galled. | Hairy.
WVieall thi yssa see ie ee tee ee ieee ee 115 121 23 49 27 3
INOLLherniS p ye Sais aes eee eee 57 8 9 33 1 4
Gan. 5 ees ce Geek Rue Oe Ree ane 77 2 48 40 2 14
HIRO Cal ees Sees ao ee a ciara nets a ce 249 131 80 122 30 21
IDE EI COTE Re eet en ces nes aren gener ee Ee 54. 1 2555 17.8 70.5 17.4 12.1

19.

20.

21.

INDEX TO LITERATURE.

. Atwoop, Wiii1aAm B. Crown-gall. Third Report of the State Entomologist,

Virginia, 1901, 33 pp. and 10 pls.

Some observations on crown-gall of apple trees. Bulletin 140, Va. Aer.
Expt. Sta., 1902, pp. 187-212 and 10 figs.

Injurious insects and plant diseases. Special Bulletin 45, Va. Aer.
Expt. Sta., Aug., 1904, pp. 17-20 and figs. 19-22.

Apple crown-gall. Rept., Md. State Hort. Soc., vol. 7, 1905, p. 114.

. Barney, L. H. Root galls. Bulletin 117, N. Y. (Cornell) Agr. Expt. Sta., 1896,

pp. 367-875 and fig. 131; also Ninth Annual Report of same station, 1897, pp.
425-434.

. Beacnu, 8S. A., Lows, V. H., and Strwart, F.C. Common diseases and insects

injurious to fruits. Bulletin 176, N. Y. (Geneva) Agr. Expt. Sta., 1899, pp.
417, 418, and 439.

. Butz, GEorGE C. Crown-gall. Rept., Pa. State College, 1901-1902, pp. 405-

412 and 1 pl., 1902.

. Cuinton, G. P. Report of the botanist. Crown-gall. Rept., Conn. Agr. Expt.

Sta., 1904, pp. 299, 309, 338, 346, and 354 and pl. 24.

. Dover, G. M. Root-knot on apple trees. Insect Life, vol. 2, 1890, p. 315.
. Forses, 8. A. The crown-gall as a nursery pest. Trans., Ill. State Hort. Soc.,

vol. 34, 1900, pp. 1386-150 and pls. 1-4.

Entomological notes and inspection report for 1901. The crown-gall.
Trans., Ill. State Hort. Soc., vol. 35, 1902, pp. 150-154.

The crown-gall. Report of the State Entomologist, Illinois, vol. 22,
1903, pp. 108-110 and 1 pl.

Report of inspection and insecticide operations. Crowngall in nur-
series. Trans., Ill. State Hort. Soc., vol. 37, 1904, pp. 229-232.

. FranxK, A. B. Die Krankheiten der Pflanzen, vol. 3, 1896, pp. 316-318.
. GARMAN, H. Diseases of nursery stock. Crown-gall. Bulletin 93, Ky. Agr.

Expt. Sta., 1901, pp. 104-106 and figs. 1-3.
Diseases of nursery stock. A knot disease of apple trees. Bulletin 93,
Ky. Agr. Expt. Sta., 1901, pp. 106-107 and fig. 4.

. GuitrorD, W. H. Root-galls. Rept., lowa State Hort. Soc., vol. 36, 1902,

p. 025.

. Hepecock, GEORGE G. Some of the results of three years’ experiments with

crown-gall. Science, n.s., vol. 22, 1905, pp. 120-121; also National Nurseryman,
vol. 13, Aug., 1905, p. 129; also American fruits, vol. 3, 1905, p. 75.

The crown-gall and hairy-root diseases of the apple tree. Bulletin
90, pt. 2, Bureau of Plant Industry, U.S. Dept. of Agriculture, Nov., 1905, 7
pp. and 3 pls.

The crown-gall and hairy-root diseases of the apple tree. Rept., Va.
State Hort. Soc., vol. 10, 1906, pp. 152-155.

Prevention of apple crown-gall and hairy-root. National Nurseryman,
vol. 15, 1907, pp. 192-193; also American Fruits, vol. 7, 1907, p. 69.

186 93

23.

24.

THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

. Hepecock, GeorGEeE G. The cross-inoculation of fruit trees and shrubs with

crown-gall. Bulletin 131, pt. 3, Bureau b: Plant Industry, U. 8. Dept. of
Agriculture, Mar., 1908, pp. 21-23.
Some son tumors or knots on apple and quince trees. Circular 3,

Bureau of Plant Industry, U.S. Dept. of AEE May, 1908, 16 pp. and |

10 figs.

Howarp, W. L. Experiments with crown-gall. Rept., Mo. State Hort. Soc.,
vol. 46, 1903, pp. 154-159; also Western Fruit Grower, vol. 14, 1904, pp. 112-113
and 5 figs.

5. Henprick, H. F. Orchard pests. Bulletin 55, Utah Agr. Expt. Sta., 1898, pp.

157-168.

. Isaac, J. Crown-gall. Rept., Cal. State Board Hort., vol. 8, 1902, pp. 77-80.
. JacosBs. Root-knot. Rept., Cal. State Board Hort., vol. 4, 1894, p. 153.
. JAEGER Jute. Ueber Kropfmaserbildung am Apfelbaum. Zeitschrift fiir

Pflanzenkrankheiten, vol. 18, 1908, pp. 257-272 and pl. 7.

. JoHNSOoN, W. G. Crown-gall. National Nurseryman, vol. 9, July, 1903, pp.

68-69.

. Kissa, N. W. Kropfmaserbildung bei Pirus malus sinensis. Zeitschrift fiir

Pflanzenkrankheiten, vol. 10, 1900, pp. 129-132 and pls. 3 and 4.

. Letone, B. M. Root-knot. Rept., Cal. State Board Hort., vol. 4, 1894, p. 313.
. Mites, GeorGE F. Diseases of the apple tree and fruit. Crown-gall. Rept.,

Nebr. State Hort. Soc., vol. 34, 1903, p. 58.

. Morris, O. M. Rept., Okla. Agr. Expt. Sta., vol. 14, 1905, p. 21.
. Norton, J. B.S. Plant diseases in Maryland in 1902. Rept., Md. State Hort.

Soc., vol. 5, 1902, pp. 92-93.
Crown-gall. Circular Bulletin 42, Md. Agr. Expt. Sta., Mar., 1902, p.
18 and fig. 10.

. ——— Crown-gall. Circular Bulletin 51, Md. Agr. Expt. Sta., Mar., 1903, pp.

1-3 and fig. 1.

.——— Crown-gall. Circular Bulletin 56, Md. Agr. Expt. Sta., Apr. and May,

1904, pp. 1-8 and pls. 1-5.

. Pappock, WENDELL. Crown-gall. Bulletin 86, Colo. Agr. Expt. Sta., Dec.,

1903, 7 pp. and 2 pls.

. Pammet, L. H. The crown-gall disease. Iowa State Register and Farmer, No.

2713, May 10, 1907, p. 4.

. Pours, J.L. Report of committee on injurious fungi. Crown-gall. Rept.,

Va. State Hort. Soc., vol. 6, 1902, pp. 145-148 and fig. 7.

Distinguish between hairy or fibrous root gall and hard root gall. Na-
tional Nurseryman, vol. 13, Sept., 1905, pp. 144-145 and fig. 1.

Recent observations on crown-gall of apple. Special Circular ‘to Vir-
ginia Nurserymen, Jan., 1907, 4 pp.

Crown-gall of the apple—the scion largely responsible. National
Nurseryman, vol. 25, Aug., 1907, p. 224.

. PopENoE, E. A. The crown-gall in Kansas. Rept., Kans. State Hort. Soc., vol.

27, 1903, pp. 134-137.
Note on crown-gall. Western Fruit Grower, vol. 15, Jan., 1904, p. 25.

. Pucstey, C. W. Diseases of the apple. Crown-gall. Rept., Nebr. State Hort.

Soc., vol. 36, 1905, pp. 241-242.

. Rrrzema-Bos, J. Wurzelkropf. Zeitschrift fiir Pflanzenkrankheiten, vol. 4,

1894, p. 97.

. SANDSTEN, E. P. Crown-gall. Rept., Wis. State Hort.Soc., vol 34, 1904, pp.

132-137.
186

64.

65.

66.

67.

68.

70.

Ac

72.

73.

INDEX TO LITERATURE. 95

. SevBy, A. D. Root and stem galls. Proc., Columbus Hort. Soc , Ohio, vol 10,

1896, p. 141 and pl. 1.

Some diseases of orchard and garden fruits. Bulletin 79, Ohio Agr. Expt.
Sia Oops L2/ and fe 7.

: Preliminary report upon diseases of the peach. Bulletin 92, Ohio Agr.
Expt. Sta., 1898, p. 214. .
- A condensed handbook of the diseases of cultivated plants in Ohio.
Bulletin 121, Ohio Agr. Expt. Sta., 1900, p. 13 and fig. 11.

. SmitH, Erwin F. Stem and root tumors. Journal of Mycology, vol. 7, 1892, pp.

93 and 376.
and TowNseEND, C.O. A plant tumor of bacterial origin. Science, n.s.,
vol. 25, Apr., 1907, pp. 671-673.

. SmitH, R. E. Plant diseases of California. Crown-gall. Report of the plant

pathologist. Bulletin 184, Cal. Agr. Expt. Sta., July, 1906, p. 247.

. SmitH, W. E. Root galls. California Fruit Grower, vol 12, Dec., 1894, p. 481.
. SoRAUER, P. Kropfmaser. Handbuch der Pflanzenkrankheiten, vol. 1, 1886,

pp. 731-734 and fig. 38.

Wurzelkropf. Handbuch der Pflanzenkrankheiten, vol. 1, 1886, pp.
737-743 and figs. 40 and 41.
Wurzelkropf. Die Schiden der einheimischen Kulturpflanzen durch
tierische und pflanzliche Schmarotzer sowie durch andere Einfltisse, 1888, pp.
117-118.

Schutz der Obstbiume gegen Krankheiten. Wurzelkropf, pp. 58-60;
Kropfmaser, pp. 58, 139-140, 1900.

Kropfmasern der Baume. Handbuch der Pflanzenkrankheiten, vol. 1,
3d ed., 1908, pp. 378-386 and fig. 58.

2. Srewart, F.C. Plant diseases. Rept., Western N. Y. Hort. Soc., vol. 46, 1901,

p. 89.

and Biopeett, F.G. A fruit disease survey of the Hudson Valley in 1899.

Bulletin 167, N. Y. (Geneva) Agr. Expt. Sta., 1899, pp. 298-299 and 304-305

and 1 pl.

Rotrs, F. M., and Hatt, F. H. A fruit disease survey of western New
York in 1900. Bulletin 191, N. Y. (Geneva) Agr. Expt. Sta., 1900, pp. 300-301
and pl. 2; also Rept., N. Y. (Geneva) Agr. Expt. Sta., 1901, pp. 176-178 and
pl. 23.

Tart, L. R. Crown-gall. Rept., Mich. Agr. Expt. Sta., for 1896, pp. 96-97, 1897.

Crown-gall. Bulletin 156, Mich. Agr. Expt. Sta., 1898, pp. 305-306.

TARNANI, J. Ueber Vorkommen von Heterodera Schachtii Schmidt und H. radi-
cicola Mill. in Russland. Centralblatt fir Bakteriologie, Parasitenkunde, und
Infektionskrankheiten, vol. 4, pt. 2, 1898, pp. 87-98.

Toumey, J. W. An inquiry into the cause and the nature of crown-gall. Bulle-
tin 33, Ariz. Agr. Expt. Sta., 1900, pp. 29-30.

Van Deman, H. E. Treatment of insectsand fungous diseases. Rept., Va. State
Agr. Soc., vol. 7, 1903, pp. 86-91.

Von ScHRENK, HERMANN. Crown-gall. Western Fruit Grower, vol. 13, Mar.,
19037 p> 111.

and Hepecock, GeorcE G. The wrapping of apple grafts and its

relation to the crown-gall disease. Bulletin 100, Bureau of Plant Industry,

U.S. Dept. of Agriculture, 1906, pp. 13-20.

Crown-gall and hairy-root diseases of the apple tree. Rept., Mo.
State Hort. Soc., vol. 49, 1907, pp. 252-253; also The Fruit Grower, vol. 18,
Jan., 1907, p. 38.

186

96 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

14:

~I
en

80

81.

Waxxer, J. H. Contributions 4 la pathologie végétale; les renflements des
branches de quelques espéces de Ribes. Archives Néerlandaises des Sciences
exactes et naturelles, vol. 23, 1889, pp. 396-400.

_ Wurttna, C. A. Crown-gall in the nursery. National Nurseryman, vol. 9, Apr.,

1901, p. 172.

Witcox, E. Mean. Diseases of the apple, peach, pear, and plum, with methods
of treatment. Bulletin 132, Ala. Agr. Expt. Sta., 1906, pp. 94-95 and 113-116
and figs. 11-16.

Woopworts, ©. W., and Wicxson, E.J: Bulletin 99, Cal. Agr. Expt. Sta., Dec.,

1892, pp. 1-4.

Sta., 1892-1894, pp. 436-440, 1894.

_ Woopworts, ©. W. Crown-knot. Rept., Cal. Agr. Expt. Sta., 1894-1895, pp.

231-232, 1896.
_ Yates, W.A. Root galls. California Fruit Grower, vol. 13, Feb,., 1895, p. FLL-

Sta., 1896, pp. 842-843.
186

Root-knots on fruit trees and vines. Rept., Cal. Agr. Expt.

Some remarks on root or stem tumors. Bulletin 39, Tex. Agr. Expt.

PLATES.

50414°—Bul. 186—10——7

97

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

DESCRIPTION OF PLATES. 99

Pirate VIII. Fig. 1.—Apple root grafts, showing nine kinds of wrapping used in the
experiments: A, Ordinary unwaxed thread; B, wrapped with thread, then coated
with grafting Wax; C, cloth wrapping, the outer end of the strip fastened down with
grafting wax; D, ordinary waxed thr ead; E, thin sheet-rubber strip with the end
cemented down; Ff, a graft without wrapping; G, waxed paper strip; H, raftia,
completely covering the union; J, ordinary raflia wrapping. Fig. 2.—Root orafts
showing excessive callus at the lower blunt end of the scions. “his callus favors
the entrance of the disease. When planted in an experiment in the greenhouse,
these root graits all developed crown-gall at the point of formation of callus.

Pirate IX. Fig. 1.—The stump of an 8-year-old Collins apple tree grown in orchard 1.
This tree, the largest in the orchard, was diseased with the woolly-knot form of
hairy-root. Fig. 2.—Apple root grafts and seedlings used in the experiments: A,
A hand-wrapped root graft; B, a machine-wrapped root graft; C and D, poorly
fitted root graits; H and F, healthy apple seedlings; G and H, apple seedlings
diseased with hairy-root.

PuatE X. Two rowsof Collins apple trees in orchard | at the age of 8 years: A, This row
was diseased with the hard form of crown-gall when set in the orchard; B, this
row was healthy when set in the orchard and remained comparatively so until the
end of the experiment.

186

Bul. 186, Bureau of Plant Industry, U. S. Dept. of Agriculture. PLATE Il.

FIG. 1.—SOFT FORM OF CROWN-GALL OF Fia. 2.—SOFT FORM OF CROWN-GALL OF
THE APPLE, FROM INOCULATION WITH THE APPLE, FROM INOCULATION WITH
ROSE GALLS. RASPBERRY GALLS.

FIG. 3.—HARD FORM OF CROWN- FIG. 4.—HARD FORM OF FiG. 5.—HARD FORM OF
GALL ON THE SCION PORTION CROWN-GALL AT THE CROWN-GALL SUR-
OF ROOT-GRAFTED APPLE LOWER END OF THE ROUNDING THE UNION
TREES. SCION IN A_ ROOT- IN A ROOT-GRAFTED

GRAFTED APPLE T REE. APPLE TREE.

Bul. 186, Bureau of Plant Industry, U. S. Dept. of Agriculture. PLATE Ill.

Fic. 1.—SIMPLE FORM OF HaiRY-RooT ON FIG. 2.—BROOM-ROOT FORMOF HairRyY-RoOoT
APPLE SEEDLINGS, TYPICAL OF THOSE ON A 2-YEAR-OLD APPLE TREE.
USED IN THE EXPERIMENTS.

FIG. 3.—HEALTHY ROOT-GRAFTED APPLE FiG. 4.—HEALTHY SEEDLING APPLE TREE
TREE, SHOWING THE TYPE OF THE WITH FIBROUS ROOTS.
HEALTHY TREES PLANTED IN THE Ex-

PERIMENTAL ORCHARDS.

aS
he

S

Bul. 186, Bureau of Plant Industry, U. S. Dept. of Agriculture, PLATE IV.

Fic. 1.—EARLY STAGE Fig. 2.—LATER STAGE FiG. 3.—EARLY STAGE OF THE
OF THE AERIAL FORM OF THE AERIAL FORM AERIAL FORM OF HAIRY-ROOT
OF HAIRY-ROOT ON OF HAIRY-ROOT ON ON AN OLDER LIMB OF THE
AN APPLE TWIG. THE SAME TWIG AS SAME TREE AS THAT FROM

THAT SHOWN IN FIG- WHICH THE TWIGS SHOWN IN

URE 1. FIGURES 1 AND 2 WERE TAKEN.

Bul. 186, Bureau of Plant Industry, U. S. Dept. of Agriculture.

PLATE V.

Fic. 1.—MATURE STAGE OF THE AERIAL FiG. 2.—ROOT PRODUCTION FROM THE
FORM OF HAIRY-ROOT ON A WINESAP AERIAL FORM OF HAIRY-ROOT ON A LIMB
SEEDLING APPLE TREE. FROM THE SAME TREE AS THAT FROM

WHICH THE LIMB SHOWN IN FIGURE 1

WAS TAKEN.

SSPE STEN eek Serewe PR LEONI ata Mie a

oe i
ening |

Bul. 186, Bureau of Plant Industry, U. S. Dept. of Agriculture. PLATE VI.

——— |

Fig. 1.—RADIAL Sec- Fia.2.—EARLY STAGE FIG. 3.—A LATER Fia. 4.—AN OLDER
TION THROUGH A OF THE SIMPLE STAGE IN THE DE- STAGE OF THE SIM-
SOFT CROWN-GALL FORM OF HAIRY- VELOPMENT OF THE 7 PLE FORM OF HAirRy-
IN AN APPLE ROOT ROOT ON AN APPLE SAME FORM AS THAT Root, MANY ROOTS
GRAFT. SEEDLING. SHOWN IN FIGURE 2. BEING HAIR-LIKE.

Fia. 5.—RADIAL SECTION THROUGH A Fic. 6.—RADIAL SECTION THROUGH A
WooLLY KNOT ORIGINATING IN A HARD CROWN-GALL ORIGINATING ON
WOUND ON THE SCION OF A ROOT- THE LOWER END OF THE SCION OF A

GRAFTED APPLE TREE. ROOT-GRAFTED APPLE TREE.

SF SSS

a SS

Bul. 186, Bureau of Plant Industry, U. S. Dept. of Agriculture. PLATE VII.

FiG. 1.—ROOT OF AN APPLE TREE GROWN FIG. 2.—ROOT OF A GRAFTED APPLE TREE
FROM A CUTTING TAKEN FROM A SEED- GROWN FROM A SCION TAKEN FROM A DISs-
LING APPLE TREE DISEASED WITH THE EASED LIMB OF THE TREE TWIGS AND A
SIMPLE FORM OF HAIRY-ROOT. LIMB OF WHICH ARE SHOWN IN PLATE IV.

Fic. 3.—Roots OF A FAMEUSE APPLE Fic. 4.—RooTs OF A JONATHAN APPLE
TREE GROWN FROM A ROOT GRAFT TREE GROWN FROM A ROOT GRAFT
WITH THE ROOT PIECE DISEASED WITH DISEASED WITH HAIRY-ROOT, BUT WITH
HairYy-RooT, BUT WITH HEALTHY NO ROOTS ON THE SCION.

ROOTS ON THE SCION.

@

Bul. 186, Bureau of Plant Industry, U. S. Dept. of Agriculture. PLATE VIII.

FIG.1.—APPLE ROOT GRAFTS SHOWING NINE KINDS OF WRAPPING USED IN THE
EXPERIMENTS.

Fic. 2.—ROOT GRAFTS LEFT TOO LONG IN STORAGE, SHOWING EXCESSIVE DEVELOPMENT
i OF CALLUS. THE SCIONS WERE CUT WITH THE LOWER TIP BLUNT.

|
|
|
Bul. 186, Bureau of Plant Industry, U. S. Dept. of Agriculture. PLATE IX.
)
;

|

;

}

|

| Fic. 1.—THE WoOOLLY-KNOT FORM OF HAIRY-ROOT ON THE CROWN OF A COLLINS APPLE
1 TREE IN ORCHARD 1.

)

4

|

4

4

|
| i .
: .
;

Fic. 2.—APPLE ROOT GRAFTS AND SEEDLINGS USED IN THE EXPERIMENTS.

PLATE X.

Bul. 186, Bureau of Plant Industry, U. S. Dept. of Agriculture.

A. A Row OF COLLINS APPLE TREES DISEASED

TYPICAL ROWS OF TREES IN ORCHARD 1:

A Row

B,

OF THE SAME VARIETY, PLANTED AT THE SAME TIME, BUT WITH HEALTHY Roots.

GALL WHEN PLANTED IN THE ORCHARD;

HARD FORM OF CROWN

WITH THE

INDEX.

Aerial form of crown-gall. See Crown-gall, aerial form.

Almond crown-gall. See Crown-gall, almond. ~ Page.
Alwood, W. B., experiments on the cure of disease..........------.--..---00- 69
observations on trees affected with crown-gall.........-.-..--- 31

statement as to the communicability of crown-gall.....-.-.... 45

Antiseptics, use on root grafts for control of crown-gall and hairy-root...... 65-66, 92
Aphis, woolly, relation to spread of crown-gall and hairy-root..............-- 49, 59
Apple, Baldwin, susceptibility to crown-gall and hairy-root..---. Bs tena 42, 85
Ben Davis, susceptibility to crown-gall and hairy-root.... 40, 41,42, 72,74, 85
enoOmimenecOrmlalhyetOOl= 2.2 ©. ...5 2 -)s- esis Sols 2 2. De ae 37

crab e\ireimia-nocwlation with crown-gall: 22... -se..25-25.+--20c22 252 44
cuttings, diseased, development of woolly-knot..... Eee aed patos 15
SISCASe Re SIstaMR VAIN bLES te ek sr ete ie ig2) Sa eo ee ee See es 40, 74, 85

Early Harvest, susceptibility to crown-gall and hairy-root...-.....--- 4]
Fameuse, susceptibility to crown-gall and hairy-root.-......-.-..------ 40, 85

Gano, susceptibility to crown-gall and hairy-root........------.----- 40, 41, 85
Grimes, susceptibility to crown-gall and hairy-root.............---- 40, 41, 85
Jonathan, susceptibility to crown-gall and hairy-root...........-.--.-- 85
Maiden Blush, susceptibility to crown-gall and hairy-root........-..- 42, 43, 85
Martha, susceptibility to crown-gall and hairy-root.-.....-.....---- 42-43, 85
Minkler, susceptibility to crown-gall and hairy-root.-.-...---...------ 42, 85
Missouri, susceptibility to crown-gall and hairy-root-..........-..----- 40, 85

Northern Spy, susceptibility to crown-gall and hairy-root.... 40,42, 72, 74, 85
Northwestern Greening, susceptibility to crown-gall and hairy-root.. 40, 42, 85

Oldenburg, susceptibility to crown-gall and hairy-root...........-.--- 41, 85

Rambo, susceptibility to crown-gall and hairy-root..................--- 85

Red June, susceptibility to crown-gall and hairy-root.-....-.-...-.-- 41, 42, 85

Rome Beauty, susceptibility to crown-gall and hairy-root..........-..- 4]

Salome, susceptibility to crown-gall and hairy-root.......-.-.---------- 40, 85

Scott Winter, susceptibility to crown-gall and hairy-root........--.--- 85

seedlings, American and foreign grown, comparison, experiments.....- 26-27
condition relative to communication of crown-gall and hairy-

HOO UE F2ao crate to ae oe re ee eee SAR. Use ES ok ec 49

miscaced. ise am .root erathingess sen re ee 23-25, 80, 82

effect of injury in development of crown-gall and hairy-root. 16-17

SLCeMMOUSE CX PETIMEM US 2 52s ie ee ee ee ees See ws 16-17

grown in old nurseries, effect on health of trees..........--- 27, 82

relation of age to development of crown-gall and hairy-root.. 17-18
selection for grafting, factor in control of crown-gall and

AMIE ROO bee crac 2s ee Se Cee ee RES, SER oeaye oe 60
transplanted in nursery, development of -crown-gall and
| GENT PSII ROYOY He eae a eae ca EN meg ee en eee ENede at 81

trees. See Trees, apple. ;
varieties, in experimental orchards for study of crown-gall and hairy-
ROO UMM OR os os a 2 winls Scece Sie ere ee eee ee era 37, 39, 85, 86

50414°—Bul. 186—10——8 101

102 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

Page.
Apple, varieties, susceptibility to crown-gall and hairy-root............ 40, 41-43, 85
Walbridge, susceptibility to crown-gall and hairy-root.............. 40, 42, 85
use in top erattine’on Wealthy applessss2=s2 25 eee eee 65
Wealthy, effect of galls, orchard at Arlington, Nebr...-...-.........-.- 36
susceptibility to crown-gall and hairy-root. 40, 41, 42, 43, 72, 74, 85, 86
top grattine swath Walmer sso 2s eee er on geen eee 65
_ Whitney, susceptibility to crown-gall and hairy-root.............-. 42, 43, 85
Wolf River, susceptibility to crown-gall and hairy-root................ 40,
41, 42, 43, 72, 74, 85, 86
Yellow Bellflower, susceptibility to crown-gall and hairy-root......... 85
Transparent, susceptibility to crown-gall and hairy-root....... 41,
42, 43, 72, 74, 85, 86
York Imperial, susceptibility to crown-gall and hairy-root............ 85
Arkansas Agricultural Experiment Station, apple trees diseased with hairy-
FOOL, ADPEATAMCes F255 oo cee Se ee ee ov
Bacterium ‘tumetactens, cause of. crowm-vallegss ee ee ee ee 15
from soft crown-gall of peach, inoculation of apple
SHSM. Se ect Re Sate Ege Oars ee en en 44
Baldwin apple. See Apple, Baldwin.
Bell, C. C., statement on appearance of orchard trees affected with crown-gall- 36.
Ben Davisapple. See Apple, Ben Davis.
Benoniapple. See Apple, Benoni.
Blair, W. 8., report on occurrence of hairy-root in Ontario..................-.. 12
iBorerssinjury toapple treess= eee ea ee eee SPR a sR ee 33, 39
Botrytis, fungus attackimestoredieraitsiees ss 6 eee ee 2 67d
iBroom-foot, description) occurrences ClCee sem sae a eee 14-15, 70, 71
Variant name Tor Wairy-TOOt. ees se ee 9
See also Hairy-root.
Brown, Nellie) investization or haity-L00bs- o> ase ee ee eee 16
Budded trees. See Trees, budded.
Budding, apple trees, method for control of crown-gall and hairy-root......... 59
recommended for certain varieties of apples......................-. 73-74
Burton, J. A., statement on effect of hairy-root on apple trees................- 37
Butz, G. C., attempt to prevent disease im-orchards5- 4-2 see ee 58
experiment with apple trees affected with galls................-- 31
experiments for, cure of Crown-gall es no ee ee ees 68-69
statement on communicability of crown-gall...........-.--..--- 45
California, propagation of apple, method recommended.................-.-.-- 19
Callus; formation, relation to erowm-palle pees eee 46-48, 66-67
on root grafts, wrapping for control of crown-gall and hairy-root......-.- 61
packing apple grafts for control of development 2). -— = are ere 67, 73
relation to wounds, experiment 29-2) 2a eee Oe eee 46-48
Central States. See States, Central.
Clinton, G. P., report on experiment for cure of crown-gall and hairy-root....- 69
Cloth, use in wrapping root grafts, method, directions, etc. ....-----..-- 61, 63, 64, 73
Copper, sulphate, use as spray for nursery bins.--.....-.-..------------.---- 59
On Toot eraltsand ScionSs:s2-+-s- oe eee eee eee 65-66, 92
Crab apple. See Apple, crab.
Crown-gall, aerial form, description, occurrence, etc.-..-.---.---------------- 15
almond, transfer to the apple, experimemtos:s2------=- -- a= =a 44
and hairy-root, affected trees to be destroyed.............-------- 73
communicability in nursery and orchard.....-. 44-57, 86
cure and prevention=.—. 2 ssc) -a-=4--- eee eee 58-70

186

paar tes ht 1.

ce fae

INDEX. 103

Page
Crown-gall and hairy-root, development by years...........-..-------------- 83
distribuiien;sumimanyee eee Seen ay so 70
earhler ACCOUMLS mC MC OR sane ee eee 2 eS 44
indey fo iierstnne ass 2: 6 Sens eee ee ok 93-96
preveutionvamd @ure 2.0) ae a2 oie ee Soe eet. 58-70
related forms, geographical distribution. ........--. 12, 70
budding as a preventive, recommendation.......-..--..---------- 73-74
eanisedo by, Bacteniumeat meng Cleneeeer estan ee aee eee eee 15
communicability in root grafts, experiments...........0.-..-.-..-- 50
decrease in nursery after first year, causes, etc _.........-..-.--..--- 54, 55
SUE SUG NUT SU pees Scie geen fe anise Sane eae eet eg a ee 16-30, 71
Gischibimem «types NOLO Maes ese eee wien Hees on avs Tee 12, 70-73
ellectionvapple treesanweshigators Glted:~.45-2-> 220-2, .6>-2e ee 30-32
SLD 008 OFAN in aiek orem reas Spel wa pin Stu een arsenal 72
expemmennts.omesumlits atalolers, i2. 222 ckleae. 5 Saw de oe Sei Pee ee 81-92
LOM Sad ESCH LOM OC CUTENCE MeLCH-. c= 4-22 a= == alee 13-14, 15-16, 70
‘hard, description, oceurrence, etc... .---..-..-. 2.22. bec eee 13-14, 70
produced byimocnibitont 224/00. i2 lees ace we Skee Soe 44
Lela OM COV SOlp Cro wll- Calle Ses os alee ra ae nays eee 15-16
ESTROUS VERY UNG 6) SR ra ge a aE Sep a ee em ees S Berea e 11
imorehards. trertment recommendations =.-\)- = 25 = os 5445- 69-70
nursery prevention, recommendations .........-----.--+---,------ 73-74
OCCUNTE EMP eae Ve Lies eh eee 2 eee pe ger et ae 70-71
peach, inoculation on apple stems, experiment-........-----....--- 44
period for maximum development in nursery.....-.-.-.----------- 29-30
DEC MEMbIOMBa WU CURCER ee Gaara ei ey meer Irena ts ae ers Nera epee 58-70
Pubieations:on. connumicalollityaseesse meme ae cies oe ae ao arn 44-46
Relatedpormres, dis trilouplOm a. eq ee ers ee ee ee ye aa 12
relationcol wounds asMMAry 25 aes oe ee oe ee a ee 72
EOplieniiay en OO tener Sean tee ee ee ak cee alc pees | ra 16
SOLt-<communicability to ditierent plamts..--5.-.--222-22-.2--2---- 45
description occurrence. CG = sata a nee oe ee 13, 70
Relatwomacosnardscrown-Callles 552 nee eee ae ab ee 15-16
study, methods and conditions of experimentation ................ 77-80
susceptibility of apple, varieties, summary.......-.--..--.-------- 7
Gy aUraeeIME MAIN OS eerie iS ee Se ee eee ee ee 9
See also Hairy-root.
@Crowi-knotevariant name for crown-eall.... 2.2... .5:.2:20.6222265- 5286-2 2 9
CurermoeprevembitousOl MISEASC 4... 02. eee toe ene So tee aes ae ere 58-70
Cuttings, apple, diseased, development of woolly-knot...........-----.----.- 15
Deep planting. See Planting.
Deman, H. E. Van, observations on trees affected with crown-gall............- 32
Dormant trees. See Trees, dormant.
Early Harvest apple. See Apple, Early Harvest.
Eastern States. See States, Eastern.
Excelsior forpacking apple-root grafts, treatment....:..........-...---..--2--- 67
Experiments, study of crown-gall and hairy-root, methods and conditions. .... 77-80
resulliis; dabbles...) 25.22.02 s. 81-92
Fameuse apple. See Apple, Fameuse.
Faurot, F. A., statement regarding trees affected with crown-gall..........---- 36
France, occurrence of wurzelkropf on apple seedlings..............---------- 12
Frank, A. B., statement on effect of wurzelkropf on apple trees........-....... 30
Fungi in packing material for root grafts, destruction............----------.-- 67

186

104 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

Page
Husarium, fungus attackine stored jeratises <= 25 cee ee ee 67
Galls, variant name for crown-gall 2 222 se ee 9
Gano apple. See Apple, Gano.

Garman, H., observation on trees affected with crown-gall.................... 31
statement on communicability of crown-gall.............0....-. 44
cure-oP crown=callles ee pe eee hes ee ee 69
Germany, forms of crown=sall: ci Sse es eee ee 11
occurence of wurzellcropl. © se ies ee ne ee ee a eee Rise 1
Grafting, defective, relation to disease, experiments...................-...--- 51-52
knife, factor in spread of crown-gall and hairy-root, experiment..... 55, 72
methods for control of crown-gall and hairy-root........ 21-22, 59-65, 72-73

root, defective, relation to development of crown-gall and hairy-
TOOG 2 ioe ie CS Cs Se Oe E Berar tee Sacer 12-73, 87
top; recommmendations:.)\..5).. -s2 2 ab a ee eee 65
Grafts, root, care in nursery bins to prevent crown-gall and hairy-root........ 59
depth of planting, effect. om trees2-2- 5 =. ee ee eee ee PAN (od
experiments and results on health of trees............-. 80, 81, 82, 83-84
fitting, factor in control of crown-gall and hairy-root.... 51-52, 60, 72, 73
inoculated: witheappleicre wan-calll eeepc eae 87
methods recommended for making, storing, and planting......... 73
packine:and- storing se sary aah arpa ee ee 66-67
planting, time, ete. .cc8 PO ee ee 67
use of seedlings from old nursery districts, experiments./........ 27-28

wrapping, factor in control of crown-gall and hairy-root........... 60-61
Greenhouse, experiments in study of crown-gall and hairy-root, methods and

GONGLIONS %- Sas ee ae ee At
with seedlings aa. Scns az os ee ee 16-17

Grimes apple. See Apple, Grimes.
Guilford, W. H., statement on communicability of crown-gall..............-- 44-45
Hairy-rootandicrown-call, index to literature. .= see eee eee 93-96
budding as a preventive, recommendation ..-......-.----....--.- 73-74
description, Oceurrence, etC-2 = Sense ee 14-15, 70-71
development,;summary<</): 4. - 52s ee eee 7a
distribution; seographicalce. = sae ee tee er 12, 70-73
effect on. apple. treés. yc. Ase ene oe aie Oe ee 32-33, 72
elimination by selection’ as22.cee 62 ee eee 19
experiments, results, tables- 0-2-2 2 ee eee 81-92
forms, relation: toieach-othere ive. ee ee eee 16
historical notes 2 22= 255 2292323 ss ee ee 11
in orchards; treatment, recommendations=2-252-2522 e ee 69-70
increase 1m nursery Im second year. 22-25 Se ee ee ee 54, 55
nursery prevention, recommendations. 32222226 so22 32 se ee 73-74
period for maximum development in nursery...-......------------ 29-30
point Of orlein IN SClOM 22.5252 eee ree 43
prévention-and: cures 226 paeen 5 tn ee ee ee ee 58-70
publications on-<commiunicabilttyeass eee ee ee 46
relation: of root formation, studless 9.2 20s a ee 48-49
relation to crown gallons se ass os eee oe eee eerie 16
simple, description, occurrence; ele-sass- -- -eeee a ae 14, 70, 71
study, methods, and conditions of experimentation .......-----.-- 77-80
susceptibility of apple varieties, summiary 92252222 = = eens eee he
Variant names 2.06.) ara. ese in, yee eee so he 2 oe eee 9

See also Crown-gall.
186

asp B ee SY

ba

Seah anette

INDEX. 105

Page
Hall, F. H., Stewart, F. C., and Rolfs, F. M., statement regarding treatment of
GUSGASCURURC CS eetia ce igi Sct 2 ony roe i renner Seer emer extant s REINS 2s: 30, 32
Hard crown-gall. See Crown-gall, hard.
iileart-robycomiucion-withncrowim-co les: 2s eee ees Oe eee aT,
Holland..oceurrence.or crown-call one Ribes-.52-2-— 9 -) aes = 11
Wurzelkropi on apple seedlings..................--.- IW
Howard We le--experiments tor Cure ol crown-callase oe: aU euns lee ete 68, 69
to test contagious nature of different galls....... 45
imiroductionntonbullegim: 9.60.) eee ee | eo ee ee 9-10
Jonathan apple. See Apple, Jonathan.
Knives, grafting and pruning, relation to crown-gall and hairy-root.........-- St, 12
Knots, root, effect on fruit trees, statement by Wickson................._...- 30
Heropimasernoceurrence my Germanys. 5 6= 8a es. ess 4 eee ees ae 2
Maiden Blush apple. See Apple, Maiden Blush.
Marshall Brothers, experiments with galled trees, Arlington, Nebr...........- 36
Martha apple. See Apple, Martha.
Minkler apple. See Apple, Minkler.
Missouri apple. See Apple, Missouri.
Morris, O. M., observations on trees affected with crown-gall................- Bt
NMosstiongpac <img roob oraits; treatment... 25.52.2250 eee: 67
New Zealand, occurrence of forms ot hairy-root..-:.........2.25..4.-. graeeedse Wy
Northern Spy apple. See Apple, Northern Spy.
Northwestern Greening apple. See Apple, Northwestern Greening.
Norton, J. B. 8., observations on trees affected with crown-gall and hairy-root. ail
statement on communicability of crown-gall..........--.... 45
Cureol-crowm-allla eo iit ae: erc tn eee 69
Nusseres. distribution: of crown-¢gall-andchairy-root. .. 225.222.2824 42. 3. ence. 12
Nursery, communicability of crown-gall and hairy-root.....................- 44-57
disease prevention, recommendations:--...2552..-. 2.522.221 22...28- 73-74
experiments in development of crown-gall and hairy-root on budded
anderoot-oraited trees sonic n ms ey eee ae ee 18-19
independent and cooperative plats, locations, etc....... 77-80
with seedlings in development of crown-gall and hairy-

SOO) ee ge rere each ee Meee ee Foe eae nC My Sl ngs Me eee IG lbe)
miereaseiwicmainy-roou 1m Second -year.-..--.-5-225522 25562538236 sees. 54-55
MEHTOCSOANSHeCEION. Caution, CtCs.. 52.62) 25552 55 jayne eee ee ee 74

root grafting as related to development of crown-gall and
ATV LOOUs Sse Noo Ge she Gl a ecietaetre yeen eee ae 7AA
to control crown-gall and hairy-root in bins.............-..- 59
relative development of each form of crown-gall and hairy-root... 19-20, 72
study of crown-gall and hairy-root, methods and conditions........-. 77-80
SUMMA hyRORe XPCTIMMCN tS - dicen 2 25 ois cite. ee pee 12
trees, decrease of crown-gall and hairy-root, results of experiments. . 89
See also Trees.

Nurserymen, losses from legislation for control of crown-gall and hairy-root. - - - 9

Oldenburg apple. See Apple, Oldenburg.
amimnipeoccurence,o Wurzelkropl . 02... /2232.5.6 2s sseoee- sesh sac ee: 12
Orchardists, observations on effect of crown-gall and hairy-root..........-.--- 35-41
Orchards, communicability of crown-gall and hairy-root............-..-.------ 44-57
effect of crown-gall and hairy-root, observations of orchardists....-.. 35-41
SUTIN 4 ie ee es rae ec es et 72
‘ experimental, for study of crown-gall and hairy-root....-......-- 37-41. 79
- experiments in development of crown-gall and hairy-root.-..........- 20-21

186

106 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TRER.

Page
Orchards, importance of choosing high-grade trees....................-..---- 165
recommendations as/toi methods) teie sce. 454 44 a ee 69-70, 74
scion, selectionjol stocks 5.22228: ue eee ee ee ey ee 52, 53, 67-68
Packing for rootigrakis, exqueriuments axe 55 5 5 ee ee 47, 48, 67, 73
Paddock, Wendell, on nursery anspection = -5.- 5 ee ne oe eee 44
Paper, waxed, use in wrapping root grafts, method........................-..- 61
Peach crown-gall. See Crown-gall, peach.
Pear, occurrence of wurzelkropi in Germany. _-.....:_..7...2. 7... "Si eel 11
Pirus mals simensis, satkected soy «crowvaas alls eee er eee eee 11
Planting, root grafts at various oe LIMES; tes Ss SOREN eee ae! 21,67, 71, 73:30
Plates, descriptions i. gee eases ee ne Se eet ae 99-100
Popenoe, E. A., experiment with sale trees affected with galls.............. oo
statement as to attempts of Kansas growers to prevent disease. 58
Propagation by budding recommended for certain varieties of apple........... 73-74
method, relation to.diséasés.- 25. stesso ee ee 1
methods recommended for different sections.........-.........2: 19
use of diseased cuttings of apple........ Moke igs SCs ys Pe ne 15
Pruning, knife, factor in spread of crown-gall and hairy-root, experiment...... 55
Publications on the communicability of crown-gall and hairy-root............ 44-46
Raha, Use: in Wrappil CmrOOtiaEAhtS=— sees 5 oe assets eer eee i ee 64
Rambo apple. See Apple, Rambo.
Recommendations) of bulletimis 222%: 22a oes eee eee 73-74
Red June apple. See Apple, Red June.
Ribes, occurrence of crown-gall in Holland=:.22 2.2 22295958 eee 11
Rolfs, F.M., Stewart, F.C., and Hall, F. H., statement regarding trees affected
with: disease: icc. 24s 508 Sane Essen eee ee ee ee 30, 32
Rome Beauty apple. See Apple, Rome Beauty.
Root galls. See Hairy-root, variant names.
erafted trees. See Trees, root-graited.
crafting. See Grafting, root.
orafts. See Graits, root.
knots. See Hairy-root, variant names.
rot, confusion with crown-calles.22 es he ee ee es 33, 37
Roots, development in trees irom diseased stock.----- 2-222 222s ee 35
relation,of growth to hairy-root.222: 2 -222--) s-ce ee) ee ee 48-49
to.injury drom“hainy-rootss.2 <4 5-222 seen See nee 40
seedling selection for grafting factor in control of hairy-root..........-- 60
selection of upper and lower for root grafts, results..............-.-.-.-- 80
Rubber, use in wrappine root, eralts: 5225-625 6-22 se ae ee eee 61
Salome apple. See Apple, Salome.
Sand, use for packing Toot oralts i225 2225.55. See ee eee 67,73
eandcten: E. P., observations on crown- -gall Scchg ale ee Geta a ne eee 31-32
Schrenk, Be ena von, investigations: 2 sc). s1 2s ee ae eS Se ee eee 10
Scion orchards. See Orchards, scion.
Scions from different localities, susceptibility to crown-gall and hairy-root..... 43, 86
diseased trees, relation to crown-gall and hairy-root....- 35, 52-538, 87-88
young and old ‘trees, results of mSe222-= 2c 3) Se eee ae 25, 26, 82
point of oriem of hamy-toot 2: 222520" ae. ee eee 43
selection, factor in control of crown-gall and hairy-root.. 42, 52, 53, 59-60, 71, 73
washing in copper-sulphate solution, experiments............-------- 92

Scott winter apple. See Apple, Scott winter.
Seedlings, apple. See Apple, seedlings.
186 é

INDEX. 107

Page
Selby, A. D., observations on treatment of trees affected with crown-gall . . ... 30
statement on communicability of crown-gall..... seagate aes 44

Simple hairy-root. See Hairy-root, simple.
Smith, E. F.,-and Townsend, C. O., investigations of the cause of crown-gall. 15, 16

experiment in inoculation of apple stems with peach crown-gall. - 44
Smith, R. E., observations on apple trees affected with crown-gall............ al
Soft crown-gall. See Crown-gall, soit. ;
SoilsmetecuonshealtinvOmtrees. 2. oss soc= se ae ete ena sere ie 28, 68, 72, 74, 83
Sorauer, P., on occurrence of wurzelkropf in Germany....-.........--.-.----- ei
Sprayine munsenyz Ins, recommend allOnee srs ese. se sas. 5 eee oe 59
States, Central, effect of crown-gall and hairy-root in the orchard, summary .-.-- 72
propagation of apple, method recommended.........-.-.---.-- 19
Eastern, effect of crown-gall and hairy-root in the orchard, summary... 72
propagation of apple, method recommended...-..-.....---.-.- 19
SiStem-GUIMOKs. / GeSCrIptlom. OCCURLENCE.WelCis. fee. 22 esis ao: = we eee 15
Stewart, F. C., Rolfs, F. M., and Hall, F. H., statement regarding treatment of
GHISCASEC MRICS yee trite ke ice tet CH ee ar ba iy tad So a les amt | aD 30, 32
Sturgis, W. C., experiment for cure of crown-gall and hairy-root.....-........- 69
Sulphate of copper. See Copper, sulphate.
Sanna aolmomlle bias ees ks Se ess de ici ole ewe nines mene 70-73
Susceptibility to crown-gall and hairy-root of scions grown in different localities 43
varieties of apple..-...-..... 41-43, 85
ANread. Use in wrap prae, KOOL eTaiise.. {05-25-52 sol ea eles = ene - 61-62, 64-65, 73
Top-grafting. See Grafting, top.
Toumey, J. W., statement on crown-gall of the almond...-.-....-..........-- 33, 44
Townsend, C. O., and Smith, E. F., investigations as to cause of crown-gall .... 15, 16
investigations as to cause of crown-gall..............-...... 15, 16
fransplamtine sapple-tkeess 1OSS, "CAUSES. .- co2 8. eat. O52 ee eal gy. S38 39
Trees, budded and root-grafted, relative development of crown-gall and hairy-
TRCXO Ik os Eas a ie ey DRS Pay ae urns eC a ae SIRs er Pe IO aS ahd See 18-19, 20, 81
Sconditiion-oroots imsorchards im atten yearss2---- 2629). = sey es eee 90
@isease-yesistamtvarleties <5 53 ese eels sek oe 40, 85
MISEASeMUUNEOKC MAG en CURC eter t iar: io, ol ete te Ge eae Nn ep ta sen ee 68-70
LORD EROS ENO CO Epa Sol ea ee es DNR wefan pe hee arene 73
dormant, stored in bundles, communicability of crown-gall and hairy-

TROD cei alse EIS we Ren a a eee eee SEI ene Ge esa 50-56
emeemonuseror diseased seedings)..5: 2.2.2.2. 5. e250 ese 24-25, 71
experiments on effect of crown-gall and hairy-root....................- 30-44
fomscionsorchard, selection and-care. .... 02.2.2... 52255. soe eee 67-68
irultgeect ol-root knots, statement by Wickson.............5.......- 30
grafted, development of disease compared with budded trees. ......... 71, 81

Pie@ On disease, Im, MUTSery.4.y. 252-25: ose Nee ee 34-35

healitiinyeandsdiseased. sizes tables: .! 5.2 1.5 see ee ee ee 83-84

maximum development of crown-gall and hairy-root by years. - 83

inealthy.and-diseased, sizes and ages, tables.......---..-.../----.---+:-- 83-84

Standeimnsorchanrds = talolesmess ey. ee =e 84-85

HSMM SeR Ye nearesma Cult VaAtlON, 940. Mle. 2 lo OSs Gees puke rn ey 67

orchard importance of choosing best grade_-2.----...----.-.-----..-- 40-41
root-grafted, development of crown-gall and hairy-root, comparison

walled dedntreess: 2a sac js 18 terial 7s eens oo eS 18-19

experiments in development of crown-gall and hairy-root.. 19-20

size, effect of different forms of crown-gall and hairy-root.. . . .- 34-35, 38, 83, 84

186

108 THE CROWN-GALL AND HAIRY-ROOT OF THE APPLE TREE.

Page.

Trees, stand, relation of defective root grafting. ~:~ 2255-25222) 4- 4 eee 50

susceptibility of varieties to disease... .... Fae a SN Soca er eu se 41-43, 85

use of hairy-root pieces in grafting, effect on stand...................-. Rs |

varieties, in experimental orchards for study of disease........... 37, 39, 85, 86

less resistant: to diseases 25257 ee eee 74

Tumors, stem, description, occurrences etee - -4. eee eee ee 15

variant name for hairy-root-: 2:5 50-22 ee See 9

Utah, crown-gall, occurrence.on budded trees-= = 2322s eee 19

Van Deman, H. E., observations on trees affected with crown-gall........... 32
Virginia crab apple. See Apple, crab, Virginia.

crown-gall, occurrence on-budded trees- 2-422 2 ee ee = ee 19

Von Schrenk, Hermann. See Schrenk, Hermann von.

Walbridge apple. See Apple, Walbridge.

Waxed paper. See Paper, waxed.

Waxing, root: gratts,, method .¢ 200-20 1s. See Sk 62
Wealthy apple. See Apple, Wealthy.

Whitney apple. See Apple, Whitney:

Wickson, E. J., statement on effect of root knots on fruit trees...............- 30
relation of development to crown-gall and hairy-

MOOG fd sel See ee ay ae rea tee eee 40

Wolf River apple. See Apple, Woli River.
Woodworth, C. W., statement on effect of crown-gall on plants................ 30
treatment of affected stock, recommendation. ............ 44
Woolly aphis. See Aphis, woolly. .
knot, description, occurrence, ete 2. 2 ie. ee eee eee ee 14, 70, 71
occurrence on trees imported from New Zealand................- 1
variant name for hairy-ro0te-s- 3) 9-22 Sia ee 9
root, variant, name for hairy-roo0t. =. 3) = Sa eee 9
Wounds; formation of callus; experiment. 22-5532. 32 9-22. eee 46-48
relation to crown-gall and hairy-root in seedlings, experiments.. 13, 16-18, 72
to be-avoided 550. Se eee eee SS ea ee 72, 74
Wrapping, root grafts, methods, experiments, results, etc....-.....-- 61-65, 74, 91-92
summary of results)... io ee ee ee 73, 74
Wurzelkropé, effect on apple -itreesan Germanys a 5e = pe 30
occurrence in foreien: coumities 2 3-- 2.52 se ee eee eee 11, 12

Yellow Bellflower apple. See Apple, Yellow Bellflower.
Transparent apple. See Apple, Yellow Transparent.
York Imperial apple. See Apple, York Imperial.
186

O