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^7

CIRCULARNo. 545 APRIL 1940

UNITED

STATES

DEPARTMENT

OF

AGRICULTURE

WASHINGTON, D.C.

PECAN

GRAFTING

METHODS

AND

WAXES

1

ByB. G. Sitton,1_{associate nomologist, Division}

ofFruitand Vegetable Crops and Diseases, BureauofPlant Industry

CONTENTS

Page

Introduction 1

Reviewof literature 1 Defects resulting fromincorrect methods of

grafting 3

Methodsofgrafting studied 9

Procedure 10

Results - 11

Page

Waxes 16

Materialsandmethods 16

Results 24

Discussion 27

Summary 28

Literature cited 28

INTRODUCTION

Itisa

common

practice totop

w

T

orknative seedlingtreesor thoseof undesirable

named

varieties of pecan (Carya pecan (Marsh.) Engl,

and

Graebn.)withvarietiesthoughttobe

more

productive, toberesistant

toinfection

by

fungi causing disease, or to bear nuts havinggreater commercialvalue.

Many

attempts to top

work

trees

have

been

un-satisfactory

owing

to partial or complete failure to establish the

new

top,to

damage

intheprocess

by

insects

and

wood

rots, toscionsbroken

out

by

wind, orto trees

weakened

by

drastic priming.

The

frequent occurrence of such unsatisfactory results warranted a study of the

grafting procedure to learn their cause

and

to devise preventive methods.

REVIEW

OF

LITERATURE

Althoughgrafting of fruit treesis averyold art, the firstsuccessful vegetative propagation of the pecan apparently

was

accomplishedin

1822

by

Landrum

(17, 18),2

who

succeededin

budding

thepecan onto

ahickory. Taylor (35) reported that thefirstpropagationof apecan

to be given a variety

name

was done

in 1846 or 1847. Pecans

from

these grafted trees were exhibited at the Centennial Exposition at

Philadelphiain1876

and

the variety

was

afterwards

named

Centennial. Taylor (34) stated that the pecan is

more

difficult topropagate than mostfruit trees,

and

that the best

method

was

annular

budding

done earlyinthe

summer

on

1-or 2-year-oldseedlings. Fuller(10)quotes

correspondence

from

P. J.

Berckmans,

a nurseryman, as stating that inhisnursery15 to25 percentofthe scionsset

by

theuseofthe

crown

graft

on

1-year-old seedlings grew.

The

term

"crown

grafting" has been used to designate a

number

of different

methods

of grafting, 1Thewriterwishestothankallthosewhohave renderedassistanceintheconductofthisexperiment;

toH.L.Craneespeciallyforreviewofthemanuscriptandvaluable suggestions; toE.P.Akinforassistance

with thefieldwork;andtoMrs.NaomiS.Webb.andMrs.HettieWatson,whofurnished thetreeson which

thegraftingwasdone.

2_{ItalicnumbersinparenthesesrefertoLiterature Cited,p. 28.}

2 4 5, U. OF

AGRICULTURE

but the

method most

commonly

so designated

was

that in whichthe

scions were set

by whip

grafting near or below the ground line, and

it is probable that this is the

method

referred to

by

Berckmans. Oliver (21) described several

methods

of

budding

the pecan

and

recommended

a modification of the patch

method

in

which

an I

incisionis

made

inthestockforreceiving the bud. Sitton (28),

work-ing with the black walnut, found that this

method was

undesirable because the presence of theflaps of bark over the patch carrying the

bud

made

itdifficulttopressthe

bud

tightlyagainst thestock.

Many

patches of barkgrew,but

most

of the

buds

diedbecause of failureto establish uniondirectly underthe bud. Easley (7)

recommended

the chip-

and

patch-bud

method

fortop working pecan trees.

Reed

(25)

stated that

more

pecan nurserytrees

have

been propagated

by

annular budding, with its modification, than

by

all other asexual

methods

combined.

Hume

(15, 16)described several

methods

ofbudding

and

grafting

and

stated that expert propagators were satisfied with 75 percent of living buds or scions, but that

most

others were less successful.

Evans

(9) probably

was

thefirsttosuggest the useof thebarkgraft

on

thepecan, althoughit

had

longbeen used with otherfruit trees, as

reported

by

Sharrock (27), Burbidge (2),

and

many

others.

The

first

report of the use

on

the pecan ofthe inlay-bark graft with the scion

nailed to the stock

was

probably

made

by Wenzel

(36) in 1924,

although the

method had

apparently been used for

some

years

previ-ously

on

fruit trees.

Wenzel

(37) called attention to defective unions that resulted from the bark-slot

method

caused

by

the bark at the

sides of the slotinterferingwith thenormal growth ofthe scions.

McMurran

(19)

and

Demaree

(6) discussed the dangerofinjury to

top-worked pecan trees

by

wood-rotting fungi that gain entrance through improperly

made

pruning

wounds and

reported that stubs are

verysusceptible to

wood

rot.

Smith

etal. (30)foundthattreesheaded

fortopworking

most

severely

had

more

wood

rot in

wounds

thantrees less severely headed; also, that the smaller

wounds had

less rot than

larger wounds. According to

Heald

(14) the wood-destroying fungi are for the

most

part parasites that gain entrance through pruning

wounds

orothermechanicalinjuries.

Many

of

them

make

their best

developmentintheheartwood;othersstart intheheartwood andlater

advance into the sapwood. Pleurotus ostreatus Fr. is classified

by

Stevens (31) as saprophytic

and

Polyporus hirsutus Fr. as a

wound

parasite. Essig (8) reported that Schizophyllum

commune

Fr. is able togain entranceinto trees through pruning

wounds

or other points of

mechanical injury,

and

Putterill (24) demonstrated that the latter

fungus is able to

grow on

living wood, which it kills.

Demaree

(6)

reported thatinfection of

wounds

canusuallybe prevented

by

painting the cut surface thoroughly with

an

antiseptic tree-wound dressing.

Inastudyofdefective graftunionsinthe apple

and

pear, Bradford

and

Sitton (1) found a close analogy between graft unions

and

the healing of

wounds

where

no

graft

was

involved.

They

report that subsequentto wounding,

new

tissueislaid

down

in definiterelation to

theremainderofthetree.

Wounds

formed

by

amputationofalateral

branch close to the

main

branch heal

by

growth of tissue from the

sidesprimarilybutalso to

some

extentfromthe basal

and

apicaledges

3

to aside limb, is similar to theamputation

wound.

Itdiffersin that healing is slower because a larger proportion of the tree above the

wound

has beencut

away;

also, thetissue readjustment

may

be

more

radical.

The

new

vascular tissue forms approximatelylongitudinally

to the

new

stem,

which

is a composite of the old

main stem and

the

new

leader.

On

the old

main

stem, opposite the

new

leader, the

new

tissue

may

be formed in a direction almost transverse to that of the

old.

Growth

on

the sideopposite isslowerthan along thesides

adja-cent to the

new

leader. There is a similar reorientation in the

new

tissue subsequent to grafting

where

the stock is cut off squarely.

Where

theunionis established

between

scion

and

stockat the top of

the stub, tissue develops

and

extends over the top adjacent to the

scion.

Where

the contactis established below the rim,

no

new wood

formsat the topofthe stock

and

the

cambium

and

barkdie.

A

scion

set so that contact is not established at the top of the stock is like cutting

back

to a small side branch

and

leaving a stub.

DEFECTS RESULTING

FROM

INCORRECT

METHODS

OF

GRAFTING

A

study

was

made

of pecan trees in various localities in Louisiana that

had

been grafted or

budded

in order to change the top to a desired variety. Included in this study were trees that apparently

had

been top

worked

with complete success

and

others that

showed

various types of defects. These defects were analyzed

and

classified to clarify the problem.

Examination

of 100pecantrees

on

which

an

attempt

had

been

made

by

the

owner

oftheorchardtotop

work

totheSuccess variety

showed

that

many

trees

had

been so drastically cut

back

that severe injury

resulted

from

sunscald

and

only a small percentage of scions lived.

Borers

and

wood-rottingfungi

had

damaged

thetreesstill further.3

The

typeofinjuryreferred to assunscald occurs

on

a portionof the

tree previously shaded but exposed to the direct raysof thesun

from

the southwest after cutting back. It apparently occurs during the growingseasonimmediatelyfollowing the cutting back, butthe effects are usuallynot observed until the following spring

when

it is evident that the bark

and

cambium

4

aredead. Chandler (5), Goff (11),

and

Harvey

(13) considered thatthe

cambium

is killed as a result of the high temperatures caused

by

the sun's rays striking the old bark under conditions thatreduce the transpiration stream. Chandler (5) reported that the temperatureof the

cambium

had

been

measured

as high as 131° F.

on

the

sunny

side ofa branch.

Harvey

(12) reported that the temperature of the

cambium

under dark-colored bark

was

higher than under light-colored bark

when

both were exposed to

sunlightinwinter. Thesereports,

and

the observations

made

during this study, indicate that if sufficient foliage is left above the area exposed to the sunlittleinjury will result.

3_{Theborersandfungi responsible}for thisdamagewerenotidentified,butthepecanborer (Cenopia

scitula(Harr.)),theAmericanplumborer(Euzophera semifuneralis (Walk.)),andthe flatheaded appletree

borer (Chrysobothrisfemorata(Oliv.))have beencollectedfromother graftedpecantreesand wereidentified

bythe DivisioncfInsectIdentification,BureauofEntomology andPlantQuarantine. Frompecanwood

showingevidenceofwood-rotting fungiPanusrudisFr.,Pleurotusostreatus Fr.,Polyporuscrispus(Pers.)

Fr.,Polyporus(Polystictus)hirsutus(Wulf.)Fr.,PoriaambiguaBres.,andSchizophyHumcommuneFr.have

beenidentifiedbyJ.A.Stevenson, DivisionofMycologyandDiseaseSurvey, BureauofPlantIndustry.

*Inthiscirculartheterms"wood,""cambium,"and "bark"areusedasgeneralterms. Thexylemof

thestemisreferred to as"wood." Nodistinction ismadebetweentheinitiatinglayer,thexylemmother

cells,andthephloemmothercells,butthe entiredifferentiating,immatureregionbetweenthexylem and

thephloemisreferred toas"cambium." Allofthetissueslying outsideofthecambiumare referredto

4

5, U.

AGRICULTURE

In the cases

examined

in this study the area injured

by

sun scald

was

attacked

by

the flatheaded appletreeborer

and

infected

by

wood-rotting fungi, usually Schizophyllum

commune.

No

evidence

was

observed to

show

whether ornot the tree

would have

recovered

from

the sunscald if the borers

and

wood-rotting fungi

had

not gained entrance.

Examination

of the grafts

made

on

these trees

showed

that the

scions

had

beeninsertedunder thebark

and

tiedinwith

waxed

cloth.

The

scionsthatgrew

had

notestablished unionattherim ofthestub.

New

growth

extended

from

the topmost point of union diagonally

Figure 1.

—

Poor unions. A,

A

defective graft 2 years after grafting. Only

onescion livedandits unionwith the stock was about2 inches belowthetop

of the stub. The stock died back and wood-rotting fungi gained entrance

and hadprogresseddown the stock formorethan 2feet. B,Sectionthrough thebaseofa sproutproduced after cuttingback alarge branch, showing the poor unionresultingfromthe thick barkonthebranch.

downward

around the stock

on

each side

and

met

on

the side of the

stockopposite the scion

from

3 to 12inchesbelowthetopofthestock.

The

part ofthe stock abovethe

new

tissue died, having been invaded

by

borers

and

wood-rotting fungi (fig. 1,A).

In another locality trees were

examined

that

had

been top

worked

by

budding into water sprouts produced after they were severely cut back. In

most

cases the water sprouts originated

some

distance from the apex of the stub; the portion

beyond

thewater sprout

had

died

and had

been invaded

by

wood-rotting fungi. Although the

scion buds were growing the trees were

weakened

by

the

wood

rot.

To

avoid such conditions careful follow-up

work

is necessary

and

should include cutting off the projecting stub close to the shoot so as to facilitate healing.

Wounds

should be treated to prevent the entranceofwood-rotting fungi.

5

Many

water sprouts were found to

have

such poor anchorage to

the parent branch because of its thick bark that they were easily

broken out.

A

shoot 1 inch indiameter

may

have

ashoulder

on

the outside of the bark

on

the parent branch 2 or 3 inches in diameter

and

may

appear to bewell anchored, butit

may

be very weak.

The

thick, tough bark of the parent branch seems to retard the

develop-ment

of the shoot

where

it passes through the bark, particularly

periclinally to the parent branch (fig. 1, B). Borers

had

gained

entrance around the point of attachment of

many

of the shoots

and

had

further

weakened

theiranchorage. Frequently suchshootsbreak outinthe wind.

These

investigationsdidnotincludeastudyof

methods

foravoiding the

weak

anchorage of shoots, but in a limited

number

of cases the rough outer bark

was

pared away, exposing the white, soft, inner bark as advocated

by

Woodard,

Romberg,

and

Willmann

(38). Shoots arising

from

under this pared area

expanded and pushed

the

soft bark

outward

and

thus established a

good

anchorage.

These

studiesdidnot

show

how much

oftherough bark

may

bepared

away

withoutinjuryto the latentbud,nor

how much

itisnecessaryto pare

away

topermit

good

anchorage.

In a third orchard, pecan treeshad been top-worked

by

the use of grafts set

on

the side of branches that were cut back, leaving astub

12 inches or

more

projecting

beyond

the graft.

These

stubs died,

and

wood-rottingfungigainedentrance. Thiscould

have

beenlargely

prevented

by

cutting the stubs close to the grafts

and

properly

pro-tectingthe

wounds

duringthe winter following thegrafting; however, instances were observed

where

wood

rot

had

progressed

downward

beyond

the point of attachment of the scion before the end of the

first growing season.

Another

objectionable feature ofthe side graft

is that it does not

form

a strong anchorage to the stock, becausethe

new

tissue islaid

down

similarly to that

on

a decapitation stub unless there are shoots

beyond

the graft, in

which

case the graft

may

grow

very slowly or die after starting. If the stub extending

beyond

the

graft is not cut off the unionis never good,

and

the

wound

made

in settingthe scionoffersan entrance forborers

and

wood-rotting fungi.

In other orchards,

where

the

method

ofgrafting

and

the

workman-shipweregood, thediebackofthe stocks

was

apparently

due

to

damage

by

borers,

which

destroyed the

cambium

and

new

callus around the top ofthe stock

and

under the scions.

Many

graftsthat

had

broken out at the union

have

been examined,

and

without exception the breakage

was

due toweakness ofthe union. All ofthe breaks

exam-inedwerecharacterized

by

lackofunionatthe top ofthestub

and

by

growth

that did not anchor the scion firmly to the stock.

Top-worked

trees that

had none

of these defects were studied

and

showed

clearly that the defects are not necessarily concomitant with top working

by

grafting.

These

studies indicate that the difficulties encountered in topworking pecans

by

grafting consists of (1) sun-scald, (2) stubs projecting

beyond

the graft or the

budded

shoot, (3) poor unionsat the top ofthe stub, (4) borersworking inthe callus

underthegraft,

and

(5)

wood

-rotting fungi.

Grafting trees involves

more

or less drastic pruning either before or after the graftingis done.

The

response of pecan trees to severe pruning

was

studied,

and

it

was

found that the dieback observed in

G OF

AGRICULTURE

growth

response of the apple

and

pear following cutting

back

to an

existing lateralhas been described

by

Bradford

and

Sitton (1),

and

a

B

C

D

j^KL

Figure2.

—

Toprevent dyingbackofcut back branchesnewxylem growth must

bemadetotheapexofthestub: A,

A

cut-backbranch withthebarkremoved to showthenewshootandthecourseofthenewxylemtissueformedafterthe woundwas made;B, 2years'xylem growthafterbranch wascutbackbeyond

a very small lateral; C, after cutting back, two sprouts grewand new xylem

tissuedeveloped along alinefromtheapical tothe basal shoot; D,graftunion

was notmade atapexof stockwhich died back.

similar response

was

observed in the pecan. Grafting, however, usually involves cutting offabranch

some

distance

beyond any

exist-inglateral,

and

the

growth

responseis

more

comparableto that

follow-7 ingthedevelopmentofwatersprouts

from

latent

buds on

adecapitated

stub. In the specimens of thelatter class examined, the orientation

ofthe

new

vasculartissue, especiallyalongitsupper margin,

was

very

different

from

thatof the old branch.

A

representative decapitation

wound

and

the

new

growth

resulting is

shown

in figure 2,

A.

The

bark has been

removed

to

show

the

new

xylem

tissue.

About

2

weeks

had

elapsedsincethe beginningof

growth

oftheshoot

when

thestub

was removed from

thetree.

The

earlystageofthechangein orienta-tion of the vascular tissue is clearly shown.

Very

little

new

tissue

developed distally to the shoot.

On

each side of the shoot the

new

tissue radiated

outward and downward, and

for about 1 inch

on

each

side ofthe shoot theupper

margin

ofthe

new

tissue

was

almost

trans-verse to the old stem.

There

it turned

downward

and

this trend increased with additional distance

from

the shoot.

At

about

two-thirdsthe distance

from

theshootto theoppositeside ofthe stub, the

margin

of the

new

tissue

was

almost parallel with the old branch.

The

margin from

the

two

sides

met

atabout 5inchesbelow the apex

of the stub.

The

old tissue

above

the

margin

of the

new

showed

decline

due

to insufficient nutrition

and

probably

would have

died within a short time.

A

more advanced

conditionof a similar

wound

is

shown

in figure 2, B.

The

portion of the stub projecting

beyond

the

new

growth

had

died, borers

and

wood-rotting fungi

had

gained entrance.

The amount

of dieback

was

greater

on

stubs larger than that

just described.

and

less

on

stubssmaller. Frequently

on

stubsabout

1 inchindiameter the

new

tissue

was

laid

down

transverse to theold

stem

almost to the opposite side

from

the shoot.

Where

thelateral

shootdeveloped attheapexofthestub a

much

smaller portionofthe stub died,

and

in

some

cases

where

the stub

was

small there

was

no

dieback.

The

development

of

more

than one shoot

on

the stub resultedin a

somewhat

differentcourseof

development

of the

new

tissues.

Where

two

shoots occurred approximately opposite each other,

which

was

rare, the

growth

from

each shoot tended to extend diagonally

down-ward around

the stub in the

manner

previously described, but fre-quently

when

about one-third the distance

between

the

two

branches

had

been covered, the

new

vascular tissues turned nearly transverse

tothestub

and

met

the

growth

from

the other branch.

The amount

ofdieback

was

notso great as

on

stubs having only oneshoot;

where

two

shoots were present

and

one developed

more

basally

on

the stub than the other, the

amount

of dieback

was

sometimes as great as

where

onlyone branchoccurredon astub,with the

margin

ofthe

new

tissueextending directly

from

the apical to the basalshoot (fig. 2, C).

The

effectofthesize

on

the stubhaving

two

shoots

was

similar tothat

for one shootin that the dieback

was

less

on

small stubs

and

greater

on

large ones.

When

a singlescion

was

set

on

a stub

and

union

was

not

made

at the apex, the

new

tissue laid

down

was

similar to that

formed

when

asingleshootgrew,

and

theportionofthestub extending

beyond

the

new

growth

died (fig. 2, D).

Where

union

was

established at the apex of the stub the dieback

was

notso extensive

and

in

many

cases there

was no

dieback (fig. 3, A).

If

no

dieback occurred the vascular tissue subsequently formed extended over the rim

and

completely covered the

wound.

Many

8 OF

AGRICULTURE

such grafts were not invaded

by

wood-rotting fungi. Frequently

grafts of one scion to the stub

had

considerable dieback if the stub

was

large. It seems advisable to set

more

than onescion ifthe stub

is

much

largerthan 1 inch in diameter.

On

stubs where

two

scions

grew

but union ofone or both

was

not completeto the apex of the stub,

some

diebackoccurred but usually

it

was

not so extensive as

where

onlyone scion grew; frequently the

final result

was

just as serious, for wood-rotting fungi invaded the deadwood,

and

once they

had

gained entrance they continued to ad-vanceintheheartwood.

Where

two

scionsunited at theapexofthe

\A

B

_:I

Figure 3.

—

Pecan graft unions with bark removed to show new tissuesformed afterthegraftsweremade:A, Only one scionwassetwith unionbeing made

almosttotheapexofthestockandnewxylemtissueextendedaroundand with-inone-eighthinchoftheapexofthe stub; B, anexcellentgraftunion inwhich

newxylem growthhas extendedacrossthetopofthestubandfirmlyanchored bothscions to the stock.

stub there

was no

dieback

and no

evidenceof

wood

rot (fig.3,B),

where

the grafted stub

was

not

more

than

3%

to 4 inches hidiameter.

On

stubs

much

over 4inchesin diameterthe

new

growthusually didnot extend to the apex of the stub for the entire circumference of the

wound,

butthere

was an

area

on

eachside

midway

betweenthescions

that died.

The amount

of dieback

was

less where

more

than

two

scions grew, but the large stubs were frequently invaded

by

wood-rotting fungi, even where there

was

no dieback.

The

grafting of large branchesresultsina larger

wound

and

exposes a greater

amount

of heartwood than does the grafting of small branches.

The

larger

the

wound

the longer the period between

wounding and

the covering

of the

wound

by

new

tissue,

and

the dead heartwood is exposed to

infection

by

fungi for a longer time. It is therefore not advisable to graft a branch at a point where it is larger than 3/2 to 4 inches in

9

METHODS

OF

GRAFTING STUDIED

Experiments were initiated in the spring of 1934 to determine the cause ofpoor unions

and

tofind a

method

of top working pecantrees

that

would

insure a high proportion of living grafts having

good

unions. Previousexperiments

and

the reportofPrice (23)

and

others indicated that the bark-graft

and

patch-bud

methods

of top

working

usually result in high percentages of grafts or

buds

that grow.

The

investigations being reported were confined to the bark graft, of

whicheightmodificationswereused,butinall

methods

thescionswere

inserted at the distal end of the cut-off stock. There are

many

modifications of the bark graft, but they are essentially variations

of

two

types.

The

scion

may

be inserted under the slit bark of the stock orit

may

be inserted in a slot or recess

made by

the removal

ofapieceofbarkofthestockofsuchsize

and

shape to

accommodate

the prepared scion.

Some

of the modifications used

have

been de-scribed

and

designated

by

name by

differentauthors; others

have

been

advocated but not given a

name.

The

modifications of the bark

graftsused in these experiments were asfollows.

A.

—

The method

generallyreferred to as barkgraft

and

apparently

firstdescribed, although

somewhat

indefinitely,

by

Sharrock {27),

and

more

recentlydescribedforuse

on

thepecan

by Evans

(9),

Reed

(26),

and Woodard, Romberg, and Willmann

(38). In this

method

most

of the

rough

bark of stock

was

pared off, exposing the light-colored

inner bark, but notthe

cambium, and

asingleverticalcutthroughthe bark

was

made

in this area.

The

scion

was

cutwith a bevel 2 to

2%

incheslong,

drawn

out to a sharp point; it

was

pointed

by

two

short

beveled sloping cuts at the

back

of the tipso thatit

would

slip under

and

raise thebarkofthestock.

The

scion

was

thenslippedunderthe bark

and

secured

by

binding it to the stock with several

wraps

of

waxed

cloth,

which was

also used to cover the cut surface of the

stock.

The

tip of the scion

and

other exposed cut surfaces not covered with cloth were covered with

a hand

grafting wax.

B.

—

A

modificationof the barkgraft assuggested

by

Weuzel

(37).

The

scion

was

prepared

and

inserted as in

method

A

but

was

nailed

tothe stockwith oneortv/osmall-caliber flathead nails three-fourths of

an

inchlong,

and

allcut surfaceswere covered witha meltedblack wax.

C.

—

The

inlay-bark graft

method,

as described

by

Peck

(22)

and

Sitton (29).

The

outer bark

was

pared

from

the stock as in

method

A

and

the scion

was

cutwith a longsloping bevel 2 to2}iincheslong.

The

basal

end

of thescion, ata point

where

it

was

about one-fourth

of

an

inch thick,

was

cutsquareacross.

The

beveled partofthe scion

was

held against thepared area

on

the stock, the bark

was

cut

and a

strip just large

enough

to

accommodate

the scion

was

removed from

thestock,formingarecesswith thecambialcells

on

the surfaceofthe

wood

exposed.

The

bevel of the scion

was

placed in the recess

againstthat surface

and

oneor

two

nailswere used tosecure thescion to thestock. Allexposed cut surfaces

on

bothscion

and

stock were covered with a melted light-colored graftingwax. (Table 3,

No.

7.)

C.

—

Same

as

C

in all respects except that a black

wax

was

used. (Table3,

No.

3.)

D.

—

The

bark-slotgraft

method

as described

by

Wenzel

(36) #

and

Woodard, Romberg, and Willmann

(38).

The

scion

was

cut with a

10

5, OF

AGRICULTURE

bevelas in

method

C, then a short bevel

was

cut

on

the opposite side of the basal end, forming a chisel edge.

The

bark of the stock

was

pared

and

cutas for

method

C

and

astripjustwide

enough

to

accom-modate

the scion

was

lifted but left attached at its basal end.

The

scion

was

slippedunderthestripofbark,nailed,

and

thestripcutatthe topofthe shortbevel. Allpartswere

waxed

as in

C

but withblackwax. E.

—

The

graft

was

made

as forC, except that it

was

covered with

waxed

cloth

and

hand

wax

asinA.

F.

—

The

graft

was

made

as forC, but the scion

was

not nailed. It

was bound

with

waxed

cloth

and

the top of the stock

was

covered with

waxed

cloth

and

hand

wax

as inA.

G.

—

The

graft

was

prepared as for C, except that the bevel

on

the scion

was

planed to

form

a perfectly flat straight surface

and

black

wax

was

used.

H.

—

The

graft

was

prepared as for

C

except that the bark at the edges of the bevel

was

pared

away

until the

cambium

apparently

was

exposed

and

black

wax

was

used. It

was

not always possible to

expose the

cambium,

forin

some

casesthe paring

may

not have been deep

enough and

inothers too deep.

I.

—

The

graft

was

prepared as for

C

except that the stock

was

cut

backin

March

about 2

months

prior to thedateof grafting.

Bradford

and

Sitton (1)

showed

the desirability ofobtainingunion

of the scion at the apexofthestock, as well as along the sides

and

at

the basal end. In order to obtain such a union the scion

must

be placedsothatcallus

from

itwillbeas close as possible tothat

from

the apexofthestock. Callusarisesonthe scionprimarilyfromtheedgeof

the

cambium

exposed

when

the bevel is

made

on

the scion. Callus

may

arise

on

thestock

from

any

uninjured cambialcellsremaining

on

the surface of the

wood

exposed

by

the removal ofthe strip of bark, but union is accomplished

most

readily

by

the tissue arising at the

margin

of the bark. In this study all of thescions wereplaced with about one-half inch of the bevel extending

beyond

the apex of the

stock.

The

bevel at that point

was

almostits full width

and

such a placement ofthe scion reduced to a

minimum

the space between the

cambium

ofthe scion

and

that at theapex ofthe stock.

Usually

two

scions were set

on

each stock, but

some

grafts were

made

with onlyone.

The

latterwere usedinthestudyofthe

forma-tion of

new wood

reported

on

pages 7

and

8.

PROCEDURE

Scion

wood

was

collected

from

the Stuart variety of pecan just

before the trees

began growth

in the spring.

The wood

was

packed

in moist

sphagnum

moss and

stored in commercial cold storage at a temperature of approximately 34° F., but at times during a part of

the storage period the temperature

was

considerably higher. This resultedinthe swellingof

many

buds

on

thescionsbefore the grafting

was

done,

and

the percentage of "take"

was

thereby materially reduced. Scion

wood

was

more

carefully selected

and

storedin 1935

and

1936. Two-year-old

wood

that

had

made

18 inches or

more

of linear

growth

duringitsfirstyear

and

that

was

between three-eighths

and

five-eighths of

an

inchindiameter

was

used.

Wood

that

seemed

to be lowin foodreserves

was

discarded.

During

the storage period in these 2 yearsthetemperature

was

approximately34°.

During

the grafting season,

wood

foreach day's

work was removed

from storage in themorning.

PECAN

GRAFTING

METHODS AND WAXES

1

Seedling pecan trees growing in the

Red

River

bottom

land were used as stocks. Graftswereinserted in the

main

trunk about 6 feet

from

the ground, at

which

height the trees averaged approximately 2}i inches in diameter witha range of

from

2 to 4 inches.

The

treeswerecloselyspaced

and

forthe

most

part

had no

branches below the point

where

thegrafts wereinserted.

Grafting

was done

in the latter part of April, as soon as the bark

of the stock slipped freely,

and was

completed within 5 days, except

in 1934 grafting

by

method

C

was done

May

30,

and methods

A,

C,

and

I were repeated

on

that date.

The

stock

was

cutoff with a

saw

and

thescions were immediatelyset

and

waxed,orotherwise covered.

Two

covering materialsforprotection ofthegrafts

from

lossof mois-turewere used atfirst.

Some

ofthe graftswere covered with

waxed

cloth

and

hand

grafting

wax;

others were covered with a meltedblack brush

wax

composed

of 5

pounds

of rosin, 1

pound

ofbeeswax,one-half

pound

oflampblack,

and

one-fourth pint of

raw

linseed oil. It soon

became

evident that theblack

wax

was

injurious to the pecan,

and

it

was

modified

by

the substitutionof talc forthe

lampblack

and by

the omission of the linseed oil.

The

waxed

cloth

was

prepared

by

im-pregnating unbleached drill with melted

hand

wax

composed

of 4 partsof rosin, 2 parts ofbeeswax,

and

1 part of tallow.

RESULTS

Data

showing

the percentage of scions growing

and

those having

good

unions for the grafting

done

in the seasonsof 1934, 1935,

and

1936 are givenin table 1.

Due

to the useofsuperior scion

wood

and

tobetterstorage conditions thepercentageofscionsthat

grew

in 1935

and

1936

was

higherthanin 1934.

Only

thosegraftswereconsidered

as having

good

unions

where

the scion

had

united with the stock at

therim ofthe

wound

on

the stock,

was

freeof

damage

by

borers

and

wind,

and

showed no

evidence of infection

by

wood-rotting fungi.

A

graft of this class is

shown

in figure 3, B.

The

most

satisfactory

method

used

was

the inlay-bark graft with thescionsnailedtothe stock

and

allexposedcut surfacescoveredwith a

wax

composed

of 5 parts rosin, 1 part beeswax,

and

one-half part

talc (table 1,

method

C). Grafts

made

by

this

method

resultedin a higher percentage ofgrowing scions

and

a higherpercentage of

good

unionsthan

any

other.

The

firstyear 90 percentof thescions set

by

this

method

grew

and

85 percent

had good

unions. This

was

much

betterthan theresultsof

any

othermethod, underconditionsthatwere not as favorable as those of later years. In the other 2 years every scionthat

grew

had

a

good

union.

No

scionset

by

this

method

broke

from

the stock as did

some

of thoseset

by

othermethods.

Grafts set

by

the

same

method

but covered with a

wax

having thetalcsubstituted

by

lampblack

asthefiller(table1,

method

C)

were

notsatisfactory, because thepercentage of scions that

grew

was

very low in 1934

and

inother years lower than with talc as thefiller. In 1934, one-fourth of a pint of

raw

linseed oil

was added

to the

wax

as

recommended

by

Cardinell

and

Bradford (4). Evidenceof injuryto

the

cambium

ofthestock

and

scions

was

observed

where

this

wax

was

used. Later experiments indicated that this injury

was due

in part

to the oil.

Unions

were not all complete to the top of the stock,

probably because the

wax

became

soft

when

exposed to sunlight

and

12

CIRCULAR

54 5, IT. S.

DEPARTMENT

OF

AGRICULTURE

Table 1.

—

Percentage of scions growing and having good unions under various methodsofgrafting

Scionssetand growing Scionshaving good unions Methodused 1934 1935 1936 1934 1935 Set Grow-ing Set Grow-ing Set Grow-ing 1936

A.

—

Scions insertedunderthebarkofthe

stock, coveredwithwaxedclothand

hand-graftingwaxwhich held the

Num-ber 90 58 20 40 25 Per-cent 63 44 '90 34 36 Nu ru-ber 100 Per-cent 94 Num-ber 52 Per-cent 44 Per-cent 85 10 6 Per-cent 25 Per-cent 10 B.—Scions insertedunderthebarkof the

stock, nailed to stock,covered with

meltedblackwax

C.

—

Scions inlayed inrecess in bark of

stock, nailed, covered with

light-58 100 60 53 50 90 87 ' 80 96 70 50 52 100 48 90 50 40 90 40 100 C.

—

Scions inlayed in recess in bark of

stock, nailed, covered with black

30

D.

—

Bark-slot graft, with lipof bark of stock extendingover lower end of scion, nailed,coveredwithblackwax. E.

—

Scions inlayed in recess in bark of

stock, nailed, covered with waxed

clothand handwax.. . _

F.

—

Scions inlayed in recess in bark of stock, not'nailed,boundwithwaxed

clothandtop ofstockcoveredwith

waxedclothand handwax.. 39

67 60 45 52 56 34 17 20 15 30

G.

—

SameasCexcept the bevelofthe scion

wasplanedbeforeinsertion;covered

H

.

—

_SameasC_exceptbarkofscionatedges

ofbevelpared,covered withblack

wax

_____

I.—Sameas C. Stockcut inMarchprior

A.

—

RepeatedMay30.

C—

RepeatedMay23_ 25 80 | SO

C

—

RepeatedMay30 72 56 20 21 I.—RepeatedMay30

r

Use

of the black

wax

the latter part of

May

was

followed

by

the low percentageof scions that grew,

and no good

unions were formed.

The

light-colored

wax

gave almost as good results at that time as earlierin theseason.

Grafts set

by

the

same method

butcovered with

waxed

cloth (table

1,

method

E) resulted in a high percentage of scions that grew, but

many

of

them

were

damaged

by

borers

and

the percentage of good

unions

was

lower than with similar grafts covered with light-colored

wax.

Of

thegrafts prepared as for the inlay

method

but not nailed,

and

covered with

waxed

clothinstead ofmelted

wax

(table 1,

method

F)

56

and

70percentofthescions set

grew

in1934

and

1935, respectively.

The

percentage of good unions

was

much

lower than for

method

C,

owing

to failure of the scion to unite at the apex of thestock

and

to

damage

by

borers. Bradford

and

Sitton (1)

showed

that union

be-tween stock

and

scion is not accomplished until their callus tissues

press with considerable force against each other.

The

waxed

cloth

apparentlyslippedorstretched

enough

sothat the

growth

of the callus tissues pushed the scion

away

from

the stock, causing a depression between the scion

and

the stock along the line of union (fig. 4, A).

13

Such

depression

was

not evident in the unions

made

by

method

C

(figs. 3,

B

7

and

4,5). Transversesections of unions similar tothatof

figure 4,

A, showed

that the scion

had

been

pushed

2 to 15

mm.

from

the stock. Frequently the first-formed group of

parenchymatous

cells arising

from

the scion were separated

from

those

from

the stock

by

a suberized layer,

and

union

was

established only as later-formed cellspressed together so that suberization didnotoccur.

A

transverse

section ofa pecan graft that

had

notestablished union at the apexof

A

3

Figure 4.

—

Defective and goodinlay bark-graft unions. A, The scionwastied

inwithwaxedcloththat didnot holdittightly tothe stockandthecallustissues

pusheditawayfromthestock; B, thescionswerenailedinandunionwas estab-lishedatthe bottom and alongboth sidesextendingto theapex ofthestock, forming a strong union. Subsequent growth has pushed over the topof the stub, firmly anchoringthescions.

the stock is

shown

in figure 5.

The

section

was

cut approximately 15

mm.

below the apex of the stub,

and

at that level there

was no

union

on

the right side of the scion.

Parenchymatous

union

had

been established at

A

on the left side, but

had

therenot been better unionbelowthispoint the graftcould not

have

survivedfor theunion

was

not complete,as indicated

by

the suberized layer atB.

The

peri-derm

that separated the stock

and

scion tissues on the right

was

lost insectioning.

When

theunion

was

not complete at theapexof the stock the

14

54 OF

AGRICULTURE

aprojecting stub

and

died back. Grafts of thiskind were extremely

susceptible to borer infestation,

which

gained entrance to the

wound

through the space between the scion

and

the stock.

Many

such

grafts were injured

by

borers after they

had

made

several months' growth,

and

many

of thegrowing scions were broken

away

from

the stock

by wind

because they did not

have

a strong anchorage to the

stock.

The

scions

may

make

agood

growth

eventhoughtheunions arenot complete to the apex of the stock,

and

this growth causes the scion tissue to be pushed over the bark at the apex of the stock.

Wenzel

(37) reported asimilar conditionbut apparently did not recognizeits

true significance, for he considered the bark of the stock interfered

with

normal

growth

and

resulted in a

weak

union. Apparently the

Figure 5.

—

Transverse section 15

mm.

belowthe apexof a pecan graftwhich had notformeda unionat thetop. Therewas nouniononthe right side atthis

level. Periderm(lost insectioning)hadseparatedthecallus tissues ofthe stock

and scion. Parenchymatousunionwasestablished atA, but asuberized layer

separated,thecallus tissuesat B. Union wasestablished ata lowerlevel.

failure of the unionat theapex of the stock is responsible for, rather than the result of, the tissue growing over the bark.

Where

union

was

establishedatthe apexofthestock, the

new

tissue

was

formed un-der the bark

and

liftedit fromthe stock (fig.4,

B)

and

in

no

case did the bark interfere with the union.

When

the bark of the stock

was

excessively thick, paring

away

part of it prior to inserting the scion

reduced theresistance ofthebark to the expansion ofthe

new

tissues

and

facilitated the growth of the tissues into a

smooth

strong union. Grafts

made by

insertingthe scionunderthe bark (table 1,

method

A)

respondedinasimilar

way

tothose

made

withthe inlaygraftwith thescionssecured

by wax

clothinstead of nailing (table 1,

method

F).

In both

methods

the percentage of growing scions

was

very nearly the

same

butofthosefailingto establishunionattherimofthe

wounds

the percentage

was

greater in

method

A. This

was

possibly due in

15

the scionover them,

and

inpart to the increased spaceover

which

it

was

necessaryforthe

new

callus ofthestockto

grow

inorderto estab-lish contactwith thecallus of the scion.

Use

of

method

A

during the latter part of the season resulted in a lowpercentage ofscions growing

and

in

no good

unions.

In 1934,

when

the

same

method

of inserting the scions

was

used except that the scions were nailed to thestock

and

the graft covered with black

wax

(table 1,

method

B), thepercentage ofgrowingscions

was

small

and no good

unions were formed.

The

injury caused

by

the black

wax

was

especially evident,

and

injury

by

borers occurred

on

every graft. This

method was

so unsatisfactory that it

was

not used after thefirstyear.

The

bark-slot graft (table 1,

method

D)

resulted in approximately

ashighpercentagesofgrowing scionsas did the inlay-barkgraft

when

the

same

covering material

was

used, but the percentages of

good

unionswere

somewhat

lower.

Growth

of callusunderthelip ofbark at the lower end of the scion lifted the lip

and

broke the

wax

cover, after

which

borers entered through the break

and

damaged

a large

number

of scions. Leaving alipofbarkisadvocated

by some

authors

(37, 38)

on

thegrounds that thefirst unionis often established there.

This

may

be true, butthe increased danger ofinjury

by

borers

makes

the practice hazardous.

No

increase in the percentage of growing

grafts

and no

saving of time in grafting resulted, so it seems

inad-visable toleavealipofbarkprotrudingoverthelower

end

ofthescion.

Planing the bevel of the scion (table 1,

method G)

resulted in

no

increasein percentage ofgrowing scions; paring the bark at the edge

of the bevel (table 1,

method

H)

reduced the percentage of

growing-scions as

compared

with the regular inlay method.

Both

of these modifications required additional time in setting of the scion,

and

since they gave

no

increased percentage of growing scions nor im-proved unionofthose that didgrow, there seemstobe

no

justification fortheir use.

Cutting

back

the stock while

dormant and some

time in

advance

of

grafting(table 1,

method

I)resultedina smaller percentageofgrowing

scions as

compared

with grafting at the time of cutting back. This

seemed

to betrue bothifthe

wound

on

the stock

was

covered with a

wound

dressing

when

cut or if it

was

left uncovered.

Buds

on

the

stock started

growth

before the grafts were

made

or soon after,

and

apparentlyinhibited callus formation around thegraft. Ifthe stocks were recut

enough

belowtheoriginalcutit

might

bepossible to avoid the stimulationcaused

by

thefirstcut. Inthisexperimentthe stocks wererecut 2 to 3inches

and

afewas

much

as 10inchesbelow thefirst

cut, but

no

record

was

made

of the responseof those cut to different

lengths because there were too few for the differences, if any, to be significant.

EFFECT OF POSITION OF SCIONS

Several practical propagators

have

said that scions placed

on

the southwestside ofa stub are

more

likelytofailthanifplaced otherwise.

While this experiment

was

not planned to give information

on

this phase, the data

show

that this

was

trueforgrafts covered with black

wax

;withother coverings thedifferencebetween thescionsgrowing

on

thesouthwest

and on

othersides

was

so small as to be within

16

CIRCULAR

545, U. S.

DEPARTMENT

OF

AGRICULTURE

in the 1935

and

1936 experiments on the effectiveness of 60 covering materials

and which have

been arranged to

show

the place effect.

A

total of 2,771 scions were set without regard to the points of the compass,

and

of these 339 were set on thesouthwest side of the stub.

Of

those scions set

on

thesouthwestside

and

coveredwith blackwax, 64 percent failed to

grow

; of those set

on

the othersides of the stubs,

only 17 percent failed to grow.

Of

the scions set

on

the southwest

side

and

covered withmaterials other than theblackwax, 21 percent

failed to grow; of those set

on

other sides

and

coveredwith the

same

materials, 20 percentfailed togrow. All scions set

and

covered with

wax

No. 5 (see table 3)

grew

whether placed

on

thesouthwest side or

elsewhere.

Table2.

—

Relationof the percentage of scionsgrowing to the -position of thescion

on. the stockinreference topointsofcompass

[Dataforseasonsof1935and1936combined]

Positionofscionandwoundcovering Scions

set Scionsgrowing

Scions

failing togrow

Scions in 60groupscoveredwith60differentmaterials,set at Number

2,771 33 121 306 2,311 Number 2,213 12 101 241 1,859 Percent 80 30 83 79 80 Percent 20 Scionsseton southwestside,coveredwithblackwax

Scionssetonothersides,coveredwithblackwax -___

Scionsseton southwestside,coveredwithmaterialsotherthan

blackwax

Scionssetonothersides,coveredwith materials otherthan

64

17 21

20

WAXES

MATERIALS

AND METHODS

Resultsofthefirstseason's

work showed

theneedofa

more

suitable

wax

for covering the pecan grafts than those tested, therefore, in-vestigationsofvarious covering materialswere undertaken. Cardinell

and

Bradford (4, p. 36) listed the qualifications for a good covering

material:

* * * (1) it would exclude air and fungi and retain the moisture of the wood; (2) itwouldcontain nomaterial thatwillinjurelivetissues inthe strength atwhichit isused; (3) itwouldnot crackincoldweather; (4) itwouldnotrunin

hot weather; (5) itwouldbe semi-permanentinpossessionofitsvarious virtues;

(6) it would have more or less elasticity to accommodate itself to changes in

dimensionofstockandcionconsequentupongrowth.

For

use

on

thepecan

two

additional characteristics areneeded: (1)

The

material

must

exclude borers,

and

(2) it

must

setquickly in the presenceofsap,becausethepecan"bleeds"

when

cutintheearly spring.

Several commercial grafting

and

wound-dressing

compounds

were obtained,

and

other materials were

made

according tovarious

pub-lished formulas. In addition,

many

original formulaswere prepared, using

some

materials that apparently

have

not been used heretofore

ingrafting

compounds.

Inthiscircularallmaterialsusedforcovering

grafts willbereferred to aswaxes, although

most

of

them had

alarger

proportionof resins than ofwaxes.

Four

laboratory tests of suitability were used in formulating

new

waxes: (1)

The

brushing or application characteristics; (2) the tem-perature atwhich the

wax

became

soft; (3) the temperature atwhich

on

a piece ofpaper.

No

attempt

was

made

to refine these tests, as

those

made

in the laboratory are inadequate, since thereal testisthe effect ofthe

wax

on

the percentageof scions thatlive, the percentage

of

good

unions,

and

freedomofthegrafts

from

insects

and

wood

rots.

The

tests

made

in the laboratorywereprimarily to

show

adjustments needed to

make

thecombinationofmaterialsworkable.

Some

ofthe

waxes

were designed to be applied in the melted condition with a brush

and

others without melting.

A

few of the latter class were applied with thehands.

It is unnecessary to list the properties of all the materials used, because

most

of

them

are standard articlesof

commerce.

One

grade

ofbeeswax, however, gavebetterresults than the otherstried. This

was

a dark-colored, tough

wax

known

as second run or

slum

gum,

and

probably contains a considerable

amount

of propolis, a gumlike material.

Scions were set

by

the inlay-bark-graft method,

two

scions per graft. Scion

wood

of the Stuart variety that

was

collected

and

stored

as previously described (p. 10)

was

used.

The

wax

formulas used,

the

number

of scions set,

and

the percentage of scions growing are

givenin table 3. Because therewereso

many

different combinations

of materials used in

making

a wax, each

wax

has been given a serial

number

to aid in discussing its value. Stocks used in series 1 were

Carya pecan seedlings of

good

growth

and

uniformity

from

sucker

growth from

the roots of trees left in

an

old nursery. These stocks varied

from

2 to 4 inches in diameter at the point

where

the grafts

were inserted.

The

stocks used in series 2 were natural seedlings of C. pecan

and

C. aquatica (Michx. f.)

Nutt

growing along a bayou.

The

treeswere not uniforminsize

and

vigor,butthoseunsuitablewere discarded.

No

detailed record

was

kept of the response of the

two

species to grafting,butit

was

apparentthat the percentageofgrowing

scions

was

less onC.aquatica than

on

C.pecan

and

that the scionsdid not

grow

as rapidly as

on

C. pecan.

18

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24

5, U.

DEPARTMENT

OF

AGRICULTURE

RESULTS

In 1935

and

1936 four of thewaxes, Nos. 5, 7, 10,

and

11, resulted in90 percent or

more

living scions;four other waxes,Nos._{2, 6, 9,}

and

62,werein this classin 1935, butdidnot giveas goodresults in 1936; Nos. 31

and

66 resulted in 94

and

90 percent _{of living scions,} respec-tively, in 1935, but through error were not usedin 1936; Nos. 45, 48, 50,

and

52 were not usedin 1935, butresulted in 92 percent or

more

of growingscions in 1936.

Considered

from

all standpoints,

wax

No.

5

was

the

most

satisfac-tory ofthosetested.

Only

5 scions of 146 setin series 1

and

covered withthis

wax

failed to

grow

; 1

was

damaged

by

a cow,

and

the others

did not

grow

because of failure of the stock to

form

callus or even water sprouts. All living scions formed unions completely to the apexofthestub

and

the

new

growth advanced

overthe

wound,

firmly

anchoring the scions. #

There

was

only oneinstance of borer

damage

and

that

was on

the scion

damaged by

thecow.

No

evidenceof

wood

rot

was

found 2

and

3 years after the

work was

done.

Results

from

the use of

wax

No.

7 were almost as good.

Only

6

scions of the 108 set

and

covered with this material failed to grow.

At

one time during the 1935 season the mixture

became

too hot

and

the talc settled out; this

may

have

been responsible forthe failures.

Where

rosin

and beeswax

were used without a filler (wax No. 1) the

percentage ofgrowing scions

was

only 56.

The

settling of the talc

from

wax

No. 7 resulted in a

wax

having characteristics similar to

thoseofNo. 1.

Waxes

Nos. 5

and

7 are very similar, having rosin

and

beeswax

in the

same

proportions (10 : 2), but they differ in that kieselguhr

was

usedas thefillerinNo. 5

and

talc inNo. 7.

The

grade ofkieselguhr used

was

a white,fluffy,

amorphous powder

having friable, spongelike particles

and

a large surface area in pro-portiontoitsweight. It

was

veryefficientin

making

the

wax

pliable

and

elastic

and

in reducing the sticky stringiness which a

beeswax-rosin

wax

without fillerhas

when

melted totheproperconsistencyfor application.

The

filler did not greatlyaffect themelting point ofthe

wax

but

by

increasing its

"body"

did prevent it from

becoming

soft

enough

to run

when

exposed to the hot sun.

The

talc used

was

the grade sold as Purified Talc, the particles of

which

were crystalline

and

even thoughfinely divided didnot

have

thelargesurface-to-mass

ratio ofthekieselguhr.5

Various other filler materials were used with different results.

Lampblack

as a filler for the rosin-beeswax mixture resulted in a materialof good brushingconsistency,

which

coveredbetterthan

any

other used.

The

percentage of growingscions

was

lowerthan where kieselguhr or talc

was

used, apparently

owing

to greater absorption

of heat

from

sunlight.

When

the air temperature ranged

from

90°

to95°F.,

wax

withlampblackas thefillerexposed tosunlight

became

soft

enough

to run

from

the graft, while under the

same

conditions

wax

withlight-coloredfillerssoftenedslightlybutdidnotrun.

When

cones of the materials were heated in

an oven

inthe laboratory,there

was no

apparentdifferenceinthetemperature atwhich mixtures with lampblack

and

kieselguhrasfillers

became

soft

enough

to run. Deter-5Afterthisexperimentwascompleted, awaxhavingaluminumpowderasthefillerinsteadofkieselguhr

butotherwise thesameaswaxNo.5wastried1year only. Theresultswereequaltothoseobtainedwith

25

minations were not

made

of the temperatures ofgrafts covered with these

two

materials

when

exposed to sunlight.

Wood-rot

infection took placevery frequently

on

grafts

where

one or bothofthe scionsfailedto

grow and

almostasfrequently

on

stubs

where

the scions

had

failed to unite at the top leaving a projecting stub that died. It is ofinterest that in series 1, graftscovered with

theblack

wax

wereinfectedonly

by

Panus

rudis,whereasthemajority

of infections in the grafts covered

by

light-colored

waxes were

by

Schizophyllum

commune.

In series 2, however, almost all of the

infection ofthegrafts

was

by

P. rudiswithoutrelation tothe covering

material.

The

additionoflinseedoilto

wax

No.

5 to

make

wax

No.

46 reduced the percentageof scions that

grew and

of

good

unions formed.

The

additionof linseedoilto

wax

No.

3,

which

had lampblack

asthefiller,

reduced thepercentage ofscions that

grew

more

than didits addition

to

wax

No.

5 (1934 data, not

shown

in table 3). Apparently theoil separated

from

the other ingredients

and

injured the

cambium.

Furthermore,the

wax

coversoftenedinthesun

and

moved

downward,

leaving the top of the stub without sufficient protection. This resultedin 31 percentofthe scions that

grew

beinginjured

by

borers,

and

in

many

cases

wood

rot followed.

The

addition of tallow to

wax

No.

5 to

make

wax

No.

45 did not materiallyalter thepercentage ofgrowingscionsin series 1,but

good

unions werefewer.

The

covering softenedinthe sunlight

and

failedto

maintain complete protection at the top of the graft, so that borers injuredabout 14percentofthe unions.

The

substitutionofparaffin of55° C.meltingpointin

wax

No.

6for

the

beeswax

in

wax

No.

5resultedinathin

and

nearlytransparent

wax

when

melted,

which

made

more

difficult a complete covering of the

graft.

The wax

was

rather brittle

when

cold

and

tended to separate

in the sun.

Although

in

some

instances the percentage of scions growing

was

as

good

asthatobtainedwiththe

beeswax

inthe mixture, the percentage of

good

unions

was

consistently lower. Paraffin used alone (No. 54)

was

veryunsatisfactory;it isamixtureofhydrocarbons that separate at a temperature of 30° to 36°

C;

apparently, one of

the constituents

was

an

oilthat injured the

cambium.

Objections

have

been raised to the use of a heated

wax

on

the grounds that it is difficult to keep it in condition for use or that it

may

killthe

cambium.

No

evidence

was

found ofinjuryto the

cam-bium

that could be assigned to the heat of the wax.

Waxes when

applied varied in temperature

from

that of the air to 130° C.

Wax

No.

52

had

tobe heated to 130° forapplication,

which

isconsiderably

above

thetemperatureusually consideredfatalto

most

plantcells,but 92 percent of the scions

grew where

this

wax

was

used.

The

best

results

were

obtained with

wax

No.

5,

which

had an

application

tem-peratureof95°to 97°.

Some

protection

from

theheat

may

have

been afforded the

cambium

by

the insulation of the bark covering it, but

thisperhaps

was

not veryeffective in

many

instances,because

most

of

thebark

was

pared

away

beforethe scion

was

inserted.

The wax

was

applied to the graft as a thin layer, seldom if ever

more

than one-sixteenthof

an

inch thick.

The

heatcarried

by

thisthinlayerof

wax

perhaps

was

insufficient to raise the temperature of the

cambium

to