THE EFFECT OF GIBBERELLIN ON THE GROSS
MORPHOLOGY, FLOWERING, AND FRUITING OF CERTAIN
HORTICULTURAL CROPS

By

JEROME HULL, JR.

AN ABSTRACT

Submitted to the School for Advanced Graduate Studies of Michigan
State University of A griculture and Applied Science
in p artial fulfillment of the requirem ents
for the degree of
DOCTOR OF PHILOSOPHY
Departm ent of H orticulture
1958

Approved

JEROME HULL, JR.

ABSTRACT

Studies were initiated to determ ine the effect of applications of
gibberellin on fruit set, rate of fruit development, ultim ate fruit size and
rate of vegetative development of the apple, cherry, peach and straw berry.
Robinson straw berry plants grown in the greenhouse and treated with 10 to
1, 000 m icrogram s of gibberellin produced elongated petioles, peduncles,
pedicels and crowns.

T reatm ents resulted in formation-of some abnormal

fruit. Achenes did not develop on such fruit. Receptacular development of
abnorm al fruit occurred not in the are a of the pistils, but in the toral tissue
acropetal to the calyx and basipetal to the are a of the p istils. Plants tr e a te d ,
with 100 m icrogram s of gibberellin in November and December produced m ore
flowers than non-treated plants. Response of straw berry plants grown in the
field and treated with 100 ppm gibberellin w ere sim ilar to greenhouse investi­
gations.
One percent lanolin paste applications of gibberellin o r indolebutyric
acid applied to the p istils of non-developing flowers on gibberellin-treated
straw berry plants produced a slight swelling of the receptacle.

The indole­

butyric acid treatm ent produced the g reater amount of swelling. The longer
the application of the lanolin paste m ixture was delayed following bloom, the
less the amount of receptacular development.
The gibberellin stim ulus did not appear to be translocated basipetally

JEROME HULL, JR.

ABSTRACT - 2

in the straw berry crown. When 500 m icrogram s of gibberellin was applied
directly to the stolon, the stimulus appeared to be translocated in both d ire c ­
tions.
Shoot length and diam eter of rooted E ast Mailing IX, XII and XVI
cuttings w ere not increased through foliar application of 100 ppm gibberellin.
Foliar applications of gibberellin applied to m ature bearing apple tre e s dur­
ing full bloom o r three weeks later did not influence fruit set or development.
All treated tre e s flowered and fruited norm ally the following season.
Shoot growth of one-year-old Mahaleb seedlings was not increased
through foliar applications of 10 to 100 m icrogram s of gibberellin applied
when shoot elongation began. O ne-year-old Montmorency cherry tre e s
sprayed with 100, 500 or 1, 000 ppm gibberellin after form ation of term inal
buds produced a second flush of growth.

Shoots of treated tre e s had g reater

fresh and dry weights than the controls.
F ruit set and development of m ature bearing Montmorency cherry
tre e s sprayed with gibberellin during full bloom, or 26 days later, were not
affected.

T rees treated while in full bloom flowered norm ally the following

season, while the post-bloom application resulted in a p artial inhibition of
flowering the following season.
Applications of 100 m icrogram s of gibberellin did not resu lt in

JEROME HULL, JR.

increased shoot elongation of seedling E lberta peach tre e s.

ABSTRACT -

F ru it set and

rate of development of m ature peach tre e s was not affected by applications
of 100 ppm gibberellin during full bloom, 26 days later, or two and one-half
months later.

While tre e s treated during full bloom flowered norm ally the

following season, the tre e s receiving post-bloom applications produced no
flowers the following spring.

THE EFFECT OF GIBBERELLIN ON THE GROSS
MORPHOLOGY, FLOWERING, AND FRUITING OF CERTAIN
HORTICULTURAL CROPS

By

JEROME HULL, JR.

A THESIS

Submitted to the School for Advanced Graduate Studies of Michigan
State U niversity of Agriculture and Applied Science
in p artial fulfillment of the requirem ents
for the degree of
DOCTOR OF PHILOSOPHY

Department of Horticulture

1958

ProQuest Number: 10008546

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G IQl i f

y*U- l o

To My
Parents
Jerome and Doris Hull

ACKNOWLEDGMENTS

The author wishes to express his sincere appreciation to all who
a ssiste d in the preparation and presentation of this work. He wishes to give
special acknowledgment to Dr. Charles L. Hamner for his guidance and super­
vision, and to Dr. A rthur E. Mitchell for his valuable criticism and sugges­
tions for which the author will never be able to tender sufficient thanks. The
w riter is indebted to Drs. Harold B. Tukey, S r ., and Leo W. M ericle for their
counsel and encouragement during the course of the investigation and p re p a ra ­
tion of this m anuscript.
Acknowledgment is given to Mr. Lowell N. Lewis, fellow graduate
student, who collaborated in the investigations with the young Montmorency
cherry trees, to Dr. John D. Downes for assistance in the statistical analysis
of data, to D rs. James E. Moulton and Robert F. Carlson for advice and sug­
gestions in conducting experim ents with straw berry plants, and to D rs. Sylvan
H. Wittwer and M artin J. Bukovac for counsel and suggestions for investiga­
tions with gibberellins.
The w riter is deeply indebted to his wife, Suzanne, for all her en ­
couragem ent and many sacrifices made throughout these investigations and
for her aid in the preparation of this m anuscript.

TABLE OF CONTENTS
Page
INTRODUCTION...........................................................................................

1

REVIEW OF L ITE R A T U R E .........................................................

4

I

F loral Initiation in Deciduous T ree F r u i t s .................................

4

F loral Initiation in the A pple........................
F loral Initiation in the C h e r r y .........................................

4

.

5

F loral Initiation in the P e a c h .................................................

5

F actors Observed to Influence Floral Initiation.................

6

F actors Affecting Straw berry M orphology..................................

9

Effect of Plant Growth Regulators on Runner Development

9

F actors Affecting Leaf D evelopm ent.....................................

9

Dormancy in the S tra w b e rry ...................................................

10

Flower Development in the S t r a w b e r r y .............................

10

Development of the Straw berry F r u i t ...................................

11

Effect of Plant Growth Regulators on Straw berry F ru it
D evelopm ent..........................................................................

12

Effect of Gibberellin on Plant D evelopm ent...................................

13

Effect of Gibberellin on Shoot D evelopm ent..........................

13

Effect of Gibberellin on Plant F resh Weight and Dry Weight 15
Effect of Gibberellin on Dormant P la n ts ................................

16

TABLE OF CONTENTS CONT’D
Page
Effect of Gibberellin on Flower In itiatio n .............................

18

Effect of G ibberellin on Pollen Development.........................

21

Effect of G ibberellin on F ruit S e t...........................................

22

METHODS AND MATERIALS......................................................................

23

Introduction...........................................................................................

23

Effect of G ibberellin on the Straw berry (F ragaria Spp.) . . .

24

Effect of G ibberellin on the Apple (Pyrus Malus L .) .................

34

Effect of G ibberellin on the C herry (Prunus Cerasus L ., and
P. Mahaleb L .) ..............................................................................

37

Shoot G row th ..............................................................................

37

Flowering and F ru itin g ............................................................

39

Effect of Gibberellin on the Peach (Prunus P ersica Batsch.). .

39

Stimulation of Seedling G row th..............................................

39

Flowering and F ru itin g ............................................................

40

RESULTS........................................................................................................

42

Straw berry Response to Applications of Gibberellin . . . .

42

Response of the Apple to Applications of G ibberellin . . . .

85

Response of the C herry to Applications of Gibberellin . . .

87

Shoot G row th...............................................................................

87

Effect on Flowering and F r u i t i n g .........................................

92

TABLE OF CONTENTS CONT'D
Page
Response of the Peach to Applications of Gibberellin . . . .

95

Effect on Se.edling G row th..........................................................

95

Effect on Flowering and F ru itin g ..............................................

95

DISCUSSION.......................................................................................................

99

SUMMARY..........................................................................................................

112

LITERATURE C IT E D ....................................................................................... 116

INTRODUCTION

The last century has been m arked by startling changes in the a g ri­
cultural industry. This revolution has been brought about mainly by a vast
accumulation of agricultural technology.

It is true that farm mechanization

has played an im portant role, but mechanization alone could not account for
the rapid advancements so recently achieved by the Am erican farm er.
Successful farm ing is no longer the livelihood of an uneducated
peasant, but is perform ed by the agricultural specialist employing many
scientific principles.

It has truly become an a rt of applied biology.

One of the m ore recent fields of study to have a wide range of
application in agriculture is that of plant growth regulators.

By employing

these compounds, scientists have found it possible to control o r regulate
the growth, development, and function of many different plants and special­
ized plant p arts.

Compounds such as naphthaleneacetic acid and 2, 4-di-

chlorophenoxyacetic acid serve as a stimulus to many plant scientists to
continue investigations of new chem ical compounds.

Such compounds are

tested for possible biological activity and subsequent p ractical applications.
i

A recent group of m etabolic compounds exhibiting potent biolo­
gical activity a re the gibberellins.

While gibberellin was firs t isolated in

1938 by Japanese chem ists (Stowe and Yamaki, 1957), it was not made

available to re se a rc h w orkers in Am erica until isolation in 1954 by a group
of United States Department of A griculture scientists (Stodola et aL , 1955).
It has since capitvated the imaginative minds and skills of scientists
throughout the nation. Experim ents were designed to determ ine its biological
capabilities and lim itations.

However, m ost of this work involved studies

with vegetable plants with very little reported on the response of pomological
crops to the use of gibberellins.
F ru it thinning, fruit set, rate of fruit development, and ultim ate
fruit size, are im portant c rite ria to pomologists. They are also interested
in the relationship of shoot and spur development in new orchard plantings
to bring tr e e s into bearing condition as early as possible, and to obtain as
much fruiting as possible on m ature fruit tre e s.

Studies were initiated to

determ ine if gibberellin might exert an influence on any of these phenomena.
Straw berries a re grown com m ercially in Michigan under the m atted
row system (Shoemaker, 1948). Experim ents w ere perform ed to ascertain
if gibberellin would resu lt in acceleration of runner development and p r o ­
duce a m atted row e a rlie r in the season in new plantings.

Com m ercial straw ­

b e rry producers and home gardeners a re continually seeking m eans of p ro ­
ducing larg e r straw b erries and obtaining g reater yields. Gibberellin was
evaluated as a possible m aterial for achieving these goals.
A griculturists are continually requesting information about new

chem ical compounds.

It was felt that these investigations would provide some

inform ation to enable agricultural scientists to render accurate judgment and
recom mendations.

4.

REVIEW OF LITERATURE

F loral Initiation in Deciduous T ree F ruits
In ord er to determ ine the influence of a plant regulator on floral
initiation in tre e fruits, one m ust firs t know when floral initiation norm ally
occurs.

Flow ers in deciduous fruit tre e s a re generally initiated the previous

season in the developing buds (Gourley and Howlett, 1941). T heir rate of
development varies, but they usually a re not completely formed until just
p rio r to anthesis the following spring.
Floral Initiation in the Apple:

F loral differentiation was observed

in the G ravenstein apple June 11 in California (Tufts and Morrow, 1925), while
in Wisconsin the firs t clear evidence of flower p a rts in the Hoadley was o b se r­
ved on June 30 (Goff, 1899). Drinkard (1909-1910) observed that the Oldenburg
started initial flower bud development about June 20. He also noted a prolonged
period of flower bud form ation and found little difference in tim e of form ation
and subsequent development of flower buds of early, medium, and late bloom­
ing apple v arieties.
Rasm ussen (1929) observed blossom bud differentiation by August 7,
1928, and July 19, 1929, in the Baldwin, while floral differentiation in the
McIntosh was evident July 29, 1928 and July 17, 1929. The year 1928 was a
rainy year, while 1929 was dry and sunny, with a prolonged drought during
p a rt of June and July.

5.

F loral Initiation in the C herry:

The firs t evidence of transition

from a vegetative to floral apex in Prunus Mahaleb at Glen Dale, Maryland,
was observed on July 29 (Tillson, 1947). Goff (1899) reported the e a rlie st
indications of flower development in King's A m arelle cherry to be July 11 in
W isconsin.

In California, Tufts and Morrow (1925) observed floral differ­

entiation in the E arly Richmond cherry on July 12.
F loral Initiation in the Peach:

Goff (1900) observed the firs t m icro ­

scopic evidence of floral form ation in the Bokara peach in Wisconsin on Sep­
tem ber 14. Quaintance (1900) found initiation of floral differentiation on
July 23 in Demming's September peach in Georgia.

D rinkard (1909-1910)

reported indications of the initial steps of flower bud development in the
L uster peach variety in Virginia on July 7. At Iowa Park, Texas, the Dr.
Burton and E arly Rose Cling peaches began initiation of floral p a rts August 10,
while Frank started September 3, and four other peach varieties first p ro ­
duced floral p a rts by September 13 (Pickett, 1942). Tufts and Morrow (1925)
in California observed the firs t evidence of floral differentiation in the E lberta
peach in late July.
Dorsey (1935), studying the development of the peach shoot in
Illinois, observed flower buds to be present in June.

He made no m icroscopic

investigations, but reached his conclusion on the basis of axillary bud fo r­
m ation and position.

6.

F actors Observed to Influence F loral Initiation:

F actors which

influence the number of floral buds initiated have been m ore thoroughly in ­
vestigated in the apple than in the stone fruits. This was probably due to
the biennial bearing habit of many of the older fruit v arieties.

That these

conditions would be applicable to the stone fruits is not necessarily true, but
would give an indication of some factors which have influenced the tim e and
number of floral buds initiated.
The leaf a re a of m ature fruit tre e s and its relationship to develop­
ing fruit has been investigated to determ ine its influence on floral initiation.
Magness (1917) defoliated several apple varieties in Oregon on June 26-28.
He observed that floral initiation would not occur and flower buds develop in
m ost v arieties in the absence of a fair amount of leaf area.

Harley, M asure

and Magness (1941) found that 58 square centim eters of healthy leaf surface
w ere required to form a blossom bud on girdled branches, while 110 to 180
square centim eters w ere required on ungirdled Yellow Newton branches.
They reported that floral initiation depends upon time of apical bud form ation.
Investigations by Struckmeyer and Roberts (1942) on Wealthy apple tre e s on
the effects of defloration and defoliation indicated that floral induction occu r­
red at least three weeks p rio r to the appearance of blossom prim ordia.
Roberts rem oved alternate leaves from new branches of Am erican
plum species over a period of tim e from July 13 to August 24. He found

blossom bud form ation to be entirely inhibited at the nodes where leaves w ere
rem oved on July 13. The inhibiting effect of defoliation decreased as the period
of defoliation became later in the season, until on August 24, the foliation
m erely resulted in a decrease of the final size of buds at the defoliated nodes.
D rinkard (1913-1914) subjected five-year-old Kings of Pippins on
Paradise stocks to various treatm ents throughout the growing season. He
found that while spring pruning tended to discourage flower bud formation,
sum m er pruning the last of June stim ulated this formation, and fall pruning
had no effect. Root pruning April 23 did not resu lt in much flower bud fo r­
mation, but if done when floral bud differentiation began, it had m arked stim u­
lation. Ringing tre e s on April 23 had no effect on floral bud formation, but
when done May 31, it resulted in a stimulation of flower bud formation.
To evaluate the effect of shading on floral initiation, Auchter et al.
(1926) covered half of Staymen and G rim es Golden apple tre e s with m uslin
cloth just before blossoming. The tre e s rem ained covered until May 15. They
found that shading prevented practically all biossom bud formation. Paddock
and Charles (1928) enclosed lim bs of Rome apple tre e s in m uslin for periods
of seven to 61 days.
form ation.

Enclosing limbs after bloom had no effect on blossom

I^imbs enclosed before bloom for one week only w ere not affected,

but when such treatm ent was extended two to seven weeks, no blossom s were
produced the next season.

/

M oisture has been observed to influence floral initiation. Gourley

/

(1915) observed that Baldwin apple tre e s produced the larg est number of blos-

v\

som buds under conditions where the m oisture was lowest during the period /■'’
of flower bud form ation. Degman et al_. (1932) found that the percentage of

(

growing points flowering was lower in irrig ated than in non-irrigated plots
for both Oldenburg and Rome Beauty.

Kirby (1918) observed that Jonathan and

G rim es Golden tre e s produced the larg est proportion of flower buds when
grown in sod.

He also noted that flower buds were differentiated e a rlie r on

sod plots than on plots receiving some cultivation each year.
Applications of plant growth regulators during the growing season
have resulted in fewer flowers the following season. In an experim ent p e r­
form ed at Beltsville, Maryland by Magness, Batjer and Baynes (1943), Winesap spurs, bearing one apple and having a secondary or new spur growth, were
treated with naphthaleneacetic acid and naphthaleneacetamide on May 26.
T reatm ent with a lanolin paste of either chemical reduced the number of
flowers initiated, but lanolin alone also reduced floral initiation.

None of

the treatm ents increased the number of flowers initiated.
A reduction in the number of flower buds form ed on m ature bearing
E lberta and Halehaven peach tre e s was found to have occurred as a resu lt of
spraying the tre e s the previous season with naphthaleneacetic acid, naphthylacetamide, or 3-chloroisopropyl-N -phenylcarbam ate, at all stages of fruit

9.

development from "shuck-off" to four weeks la te r (Kelley, 1955). The g re a t­
est reduction in number of flower buds was observed for tre e s sprayed four
weeks after "shuck-off".

Lombard (1958) observed that Redhaven peach tre e s

sprayed with 30 ppm naphthaleneacetic acid 42 days after bloom in 1957 had
significantly sm aller number of flower buds on their term inal growth in 1958.

F actors Affecting Straw berry Morphology
The straw berry plant in the vegetative condition is a monopodium.
Under a 14-hour day and 10-hour night, the plant rem ains vegetative and p ro ­
duces runners.

A 10-hour photoperiod and 14-hour dark period resu lt in the

initiation of flowers.
Effect of Plant Growth Regulators on Runnder Development: Carlson
and Moulton (1951) observed a 46 and 91 percent reduction in the number of ru n ­
n ers and retardation of growth of P rem ier straw berry plants through application
of 2, 4-D and one-half and two pounds p e r acre respectively.

Except for ru n ­

n er reduction, the plants appeared norm al at the end of the growing season.
While isopropyl-N -phenylcarbam ate at 5, 10 and 15 pounds p e r acre also r e ­
duced the number of runners form ed with no apparent injury to the plants,
dichloral urea, nine pounds p e r acre, greatly reduced runner production.
F acto rs Affecting Leaf Development:

Darrow (1930) observed that

leaf size increased in succeeding leaves developing from April to June in
Howard 17 plants, and that leaf size dropped off then in plants producing runners,

10.

but not in plants which had th eir runners removed. He found the lim iting fac­
to r of plant growth to be generally tem perature. The highest rate of leaf p ro ­
duction occurred between 68 and 79°F.
Went (1957) observed that increasing the tem perature from 10 to 20° C,
and the photoperiod from 8 to 16 hours, increased the size of leaflets and length
of petioles.

He found the rev e rse to be true in peduncle elongation.

Longer

petioles w ere observed during periods of runner form ation than during periods
of flower initiation.
Dormancy in the Strawberry:

Darrow and Waldo (1933) reported

that ordinary varieties go into a re s t period under very short daily light periods
and low tem peratures in the fall. When the light period was lengthened in the
greenhouse the first of September, all v a rieties tested made vigorous vegeta­
tive growth throughout the entire winter and required no re s t period.
Flower Development in the Strawberry:

Schilletter and Rickey (1929)

observed that the first five runner plants produced, all form ed approxim ately
the same number of flowers.

The third runner plant produced slightly m ore

flowers than any of the other runner plants; otherwise, there was a general
decrease from the firs t to the tenth runner plant, falling rapidly after the
fifth runner plant.
Lack of pollination is not the only reason that some flowers fail to
produce fruit.

Wray (1861) reported three types of straw berry seedlings:

stam inates, pistillates, and herm aphrodites.

According to Darrow (1925), a

great variation in the setting of fruit was found in the perfect flowered v a rie ­
ties, resulting chiefly from ste rile p istils.

He concluded that, under m ost

conditions, p istil sterility seem s to be determ ined in the fall (Darrow, 1927).
Five herm aphrodite varieties w ere rooted at intervals from July 15 to Sep­
tem ber 9. In every variety an increase in the percentage of flowers not se t­
ting fruit was evident in the la ter rooted plants.

He observed some v arieties

to vary in amount of sterility when planted in different soil types, and thought
this may have been one factor of sterility.

However, the soil types were ob­

tained by planting in different locations, and therefore the cause of sterility
might have been due to location o r nutrition.
It is possible that p istil sterility may be responsible for failure of
m ost straw berry flowers to form fruit.

Valleau (1918) theorized that h erm a­

phrodite straw berry v arieties may have been derived from stam inate form s
rath e r than pistillate.

Therefore, the p istil of the flower would probably be

m ore likely to be influenced by adverse environmental conditions. He noticed
that varieties with a high percentage of aborted pollen grains still produced a
portion of functional grains.
Development of the Straw berry Fruit:

The straw berry fruit is an

aggregate fruit in which the individual fruitlets are the achenes and the edible
portion is composed largely of receptacle or torus tissue.

The principal tissu es

concerned in the development of the fleshy receptacle a re the cortex and
pith.
Havis (1943) observed that the cortex developed m ore rapidly than
the pith. While some cell division occurred in the pith during the entire p e r­
iod of development of the fruit, m ost of the cell division in the cortex ceased
shortly before anthesis.

v

Effect of Plant Growth Regulators on Straw berry F ruit Development:
G ardner and M arth (1937) sprayed a p istillate straw berry selection during a
portion of its blooming period with 0.1, 0. 05, 0. 025, 0. 01 and 0. 005 percent
concentrations, respectively, of indoleacetic acid. All concentrations resulted
in many of the blossom s producing apparently norm al achenes, which proved
to be devoid of em bryos. With concentrations of 0.05 and 0.1 percent indole­
acetic acid, a number of the receptacles developed and ripened into apparently
norm al fruits.

However, never m ore than one fruit of an inflorescence de­

veloped completely. At the lower concentrations, the receptacles made only
a slight initial growth, which soon ceased, although the achenes usually de­
veloped. They planted several hundred achenes and obtained only one rath e r
weak seedling.
Hunter (1941) sprayed individual blossom s of three p istillate v a rie ­
ties, Louise, Portia and Simcoe, with 1.0, 0. 5 and 0. 25 percent indoleburyric
acid, 1 - nap hthy lace tic acid and colchicine. Parthenocarpic fru its were

13.

produced in abundance from all concentrations of indolebutyric acid and the
lower concentrations of the other two chem icals. The one percent 1-naphthylacetic acid application initiated fruit development, but injured the pedicels
so severely that m ost fruits did not reach m aturity. An application of one
percent colchicine caused no damage, but it did not stim ulate the development
of the fruits.

Unlike G ardner and M artin (1937), Hunter was able to obtain

m ore than one fruit p e r inflorescence.

The "seeds" w ere sown as soon as the

fruit was ripe, but only one plant was obtained.
Removing the achenes from the straw berry receptacle has been
reported to a rr e s t the enlargem ent of the receptacle (Nitsch, 1949). When
the achenes of the M arshall straw berry w ere removed nine days after pollin­
ation and the "berry" coated with lanolin paste containing 100 ppm of betanaphthoxyacetic acid, the treated straw berry developed and ripened in the
same m anner as the non-treated fruit (Nitsch, 1950). A 0. 3 percent betaindolebutyric lanolin paste was very effective also.
The Effect of Gibberellin on Plant Development
Effect of Gibberellin on Shoot Development: A wide variety of plants
respond to applications of gibberellin by an increase in growth.

Marth, Audia

and M itchell (1956) made a survey of the response of plants of various genera
and species of gibberellin, and observed m arked differences in the respon­
siveness of the different plants.

The m ost obvious effect was an increase in

stem elongation with longer internodes. The greatest amount of elongation
was obtained when plants w ere treated just at the beginning of stem elongation.
Brian and Hemming (1955) applied gibberellin to the foliage of pea
seedling varieties at concentrations ranging from 0. 3 to 10. 2 m icrogram s p er
plant. They observed differences not only due to treatm ents and varieties,
but to interactions of both.

The slower growing v arieties exhibited a g reater

response to the m aterial. The distinction between tall and dwarf varieties
was virtually elim inated by applications of gibberellin.
Kemp et al_. (1957) reported that gibberellin dosages below one
m icrogram p er plant would produce visible effects, while dosages of 100 m icro ­
gram s o r m ore had essentially the same initial effects, but the effects p e r ­
sisted over a longer span of tim e.

They reported gibberellin to be readily ab­

sorbed by intact plants through th eir roots, epiderm is of stem s, and leaves.
It was found to be highly mobile in intact plants and to prom ote elongation of
stem s, petioles, and to a le s se r degree, leaf blades.
Gray (1957) also observed alteration of leaf shape and size follow­
ing treatm ent with gibberellin. The leaf m argin of the tomato became smooth
rath e r than indented. African violet leaves were longer and narrow er, while
the Pinto bean retained its norm al shape, but developed larg e r leaves. These
plants also had longer leaf petioles.

Effect of G ibberellin on Plant F re sh Weight and Dry Weight:

While

the references to shoot elongation as affected by gibberellin applications usually
have been consistent, the published investigations on fresh weights and dry
weights have not always been in agreem ent.

Brian et ah (1954) grew peas and

wheat in solution culture and added gibberellin to the solution. They obtained
an increase in fresh and dry weights of the shoots, but a reduction of both
fresh and dry weights in the roots.
Leben and Barton (1956) reported an increase in both fresh and dry
weights of Kentucky Bluegrass when treated with gibberellin at 28, 56 or 112
gram s p e r acre. G rassland in A ustralia treated with two ounces of gibberellin
p e r acre, yielded an increase in dry weight in the first cutting.

However,

there was a decrease in the dry weight of the treated plots in the second cut­
ting.

This would seem to indicate that either the effect of the gibberellin ap­

plication had disappeared o r that the plants had exhausted th eir reserv e food
supply in producing the increased yield in the firs t cutting.
Bukovac and Wittwer (1956) obtained a 50 percent increase in both
the fresh and dry weights of celery in 30 days using gibberellin at 250 or 500
ppm. They did not achieve this with pea, bean, tomato, sweet corn, cucumber,
lettuce o r cabbage. Gray (1957) reported increased fresh and dry weights in
the Pinto bean within one week from foliar applications of 10 and 100 ppm of
gibberellin. M arth, Audia and M itchell (1956) found that one ppm of gibberellin

as a foliar spray increased the fresh and dry weights of the soybean in one
week.

However, there were no differences after two weeks.
The differences or lack of differences reported for fresh and dry

weights of plants treated,w ith gibberellin might be the result of time of sam p­
ling.

Since the effect of gibberellin, especially at low concentrations, is of

short duration, weights may not differ at the final harvest, yet may vary con­
siderably for a short period of time after treatm ent.

F ailure to obtain an in­

c re ase in weight may also be partially related to the nature of plant response.
Effect of Gibberellin on Dormant Plants: Plants have been induced
through applications of gibberellin into active growth under conditions not ususally conducive for such active growth.

Intact seeds of Malus Arnoldiana Sarg.

require pretreatm ent in a m oist medium at 5ftC for at least four w eeks--a p r e ­
treatm ent re fe rre d to as after-ripening.

Barton (1956), using both aqueous

solutions and lanolin paste applications of gibberellin, overcam e the physiolo­
gical dwarf condition of the non-afterripened em bryos.

She reported that the

extension of the internodes of the treated seedlings was evident within 14 days
after treatm ent.

However, the internodes of non-treated seedlings began to

elongate with increasing age and approximated the length of the treated seed­
lings after 50 days.
Epicotyl dormancy of tre e peony seedlings was broken by applications
of 1, 10, o r 100 m icrogram s gibberellin to the hypocotyl of the germ inated

seed, replacing the need of after-ripening usually accomplished by low tem ­
p e ra tu re treatm ents (Barton and Chandler, 1957).

Lippert et al. (1958) stated

that a condition of physiological re s t prevails in potatoes from tim e of tuber
initiation until six to twelve weeks after harvest, depending on varietal c h a r­
a cteristic s.

F oliar applications of 100 and 500 ppm gibberellin applied to the

plants two and four weeks before harvest resulted in sprouting and secondary
tuber form ation on the m ain tubers.
Donoho and Walker (1957) stated that the E lberta peach tre e needs an
exposure tim e of 950 hours at a ir tem peratures below 45*F to break its re s t
period and resum e active vegetative growth in tre e s that had received less than
20 percent of th eir chilling requirem ent by two foliar applications of 1, 000 and
4, 000 ppm gibberellin.

Furtherm ore, tre e s which had received 50 percent of

the necessary hours of chilling tem peratures made active vegetative growth
following four foliar applications of 200 ppm gibberellin made at 10-day in te r­
vals.
Cooper (1957) applied a 100 ppm spray of gibberellin December 15 to
young grapefruit tre e s with dormant buds. This resulted in a flush of new
growth in all the lateral buds on the term inal shoot within 15 days (December
30), while buds on non-treated tre e s showed no sign of growth until 25 days
la ter (January 25).

,

Slash pine (Pinus elliottii) tree s, growing under 16-hour day length,

w ere induced into a dormant condition when grown under an eight-hour photo­
period for two to four weeks. This dormancy was broken subsequently by a
0.1 percent gibberellin application (Bourdeau, 1958). Dormancy, induced and
maintained in the Camellia by short day conditions, was broken by periodic
applications of gibberellin (Lockhart and Bonner, 1957).
The response of certain woody ornam ental plants to gibberellin has
been reported by McVey and Wittwer (1958). They found that single foliar
applications of 1, 000 ppm or weekly treatm ents of 100 ppm resulted in a
second flush of growth in Enonymus fortunei vegetus. Magnolia soulageana
in turn produced an additional flush of growth from weekly applications of
100 ppm gibberellin and from single applications of both 100 and 1, 000 ppm.
Increases in term inal growth of woody ornam entals, they stated, was accom ­
plished by the development of longer internodes and an increased number of
nodes.
The Effect of Gibberellin on Flower Initiation:

The use of the gibber-

ellins has created startlin g effects on the flowering of biennial and long day
photoperiodic plants.

Lang (1956) obtained flowering of the biennial Hyoscyamus

niger without subjecting the plant to a cold period, when he applied five daily
applications of gibberellin of two m icrogram s each, applied to the center of
the plant rosette.
Bukovac and W ittwer (1957) produced flowering in c arro ts, cabbage,

kale, turnips, collards, and beets with two to ten treatm ents of gibberellin,
applied to the foliage o r plant apex. Except for c arro ts, they did not obtain
complete induction of flowering unless the plants w ere grown at tem peratures
approaching those commonly required for flower induction.
Harrington, Rappaport and Hood (1957) obtained flowering in non­
vernalized endive following weekly applications of 50 m icrogram s of gibberellin
p e r plant. They found that the treated plants produced longer seed stalks, long
peduncles, and sm aller flowers.

C arr et al. (1957), in A ustralia, were able

to replace the requirem ent for vernalization in Centaurium minus Moench
with 15 daily applications of gibberellin applied to the plant rosette.
Burk and Tso (1958), in Maryland, observed that flowering of the non­
ro sette Nicotiana species (short-day plant) was not affected by gibberellin,
while the rosette-type species (long-day plants), flowered e a rlie r as a resu lt
of the gibberellin treatm ents.

Wittwer and Bukovac (1957) obtained flowering

in lettuce, endive, radish, m ustard, spinach, and dill, growing under noninductive short photoperiods, by treating them with gibberellin. When these
vegetables were treated with gibberellin and grown under long photoperiods,
all but spinach and dill flowered e a rlie r than the control plants.
While gibberellin has not prom oted flowering of short day plants when
grown under long day photoperiods, it has som etim es enhanced flowering of
short day plants that have been under some lim iting environmental conditions.

Lincoln and Hamner (1958) observed chat the flowering response of intact
Xanthium plants (short-day plants) with a full complement of young leaves
and actively growing buds was not altered by foliar applications of gibberellin.
The flowering response was increased, however, when gibberellin was applied
to plants under conditions in which the flowering response would be re stric te d
by the slow growth activity of the epicotyl. Greulach and Haesloop (1958)
found that gibberellin could not be substituted for any short day requirem ent
of Xanthium necessary for the initiation of reproductive development.

How­

ever, it could substitute for additional photoinductive cycles when coupled
with one short day.
Cathey and Stuart (1958) investigated the response of Chrysanthemum
v arieties to applications of gibberellin used at different tim es during the nine
to ten week period of short photoperiods required for flowering. They ob­
tained the greatest amount of stem elongation from plants treated during the
third week. Rapid stem elongation was related to a decreased number of
latera l inflorescences. Peduncle elongation was m ost pronounced when ap­
plications of gibberellin were made in the fourth week and e a rlie r flower
development resulted from applications made in the seventh week.
Bukovac, Wittwer and Teubner (1957) studied the flowering response
of tom atoes to applications of gibberellin, and observed that the use of gibber­
ellin resulted in an increase in the number of nodes to the flowering stage,

but as a resu lt of accelerated growth, the treated plants flowered e arlie r.
The number of flowers in the first cluster of the treated plants was reduced.
Effect of G ibberellin on Pollen Development:

Chandler (1957) g e r­

m inated pollen-on agar containing 31 to 1, 000 gram s of gibberellin p er liter
of medium. Nine plants gave no germination on either the control o r gibber­
ellin media. Germination of Lilium pollen was stim ulated on the gibberellin
medium over the control. Pollen germ ination from 10 plants was inhibited
by all concentrations of gibberellin, but the pollen responded by coiling, en­
larging of the tips of the tubes, and even exuding of the cytoplasm. Pollen
from seven plants showed an increase in percentage of germ ination and a
m arked increase in tube length, when germ inated on agar media containing
gibberellin.
Vasil (1957), in India, excised the anthers of Allium cep a at leptotenezygotene o r even at leptotene and grew them satisfactorily in media containing
gibberellin.
spores.

The excised anthers produced tetrads and one-celled m ic ro -

In all other plants investigated, the anthers excised at the leptotene-

zygotene stage failed to develop.
Harrington, Rappaport and Hood (1957) observed that endive treated with
gibberellin produced sm all flowers with brownish stam ens and very little pollen.
Pollen stained with acetocarm ine was pink, indicating that it should be viable,
but no seed developed. Nelson and Rossman (1958) induced various degrees of

m ale sterility in m aize by foliar applications of gibberellin at 500 to 2, 500 ppm.
They thought the critic a l stage of plant development for m ost effective chem i­
cal induction of m ale ste rility to be when the im m ature male inflorescence was
approxim ately one inch in length.

Silks of treated plants were functional.

Effect of G ibberellin on F ru it Set:

Persson and Rappaport (1958) pruned

the m ain stem on a m ale-ste rile tomato to force two shoots from the cotyledona ry axils, and then compared treatm ents of 100 m icrogram s of gibberellin to
the stem apex, the peduncle of single inflorescence, and the firs t or second
fully expanded leaf above the second open flower clu ster of one of the laterals.
They observed an increase in the set of parthenocarpic fruit on both the treated
and non-treated latera ls when gibberellin was applied to the foliage.

T reating

the peduncles was not observed to result in an increase in the set of partheno­
carpic fruit. An application of 100 m illigram s of gibberellin to the soil resulted
in the g reatest amount of fruit set.

Rappaport (1957) reported increased fruit

set, both norm al and parthenocarpic, for the Earlypak tomato following foliar
treatm ents of gibberellin.

Spraying the fruit did not increase its size.

Thompson Seedless grapes sprayed after fruit set with 20 and 50 ppm
of gibberellin produced very large b e rrie s and b erry clu sters (Weaver, 1958).
Flowering clu sters of Black Corinth grapes w ere dipped into solutions ranging
from one to 500 ppm of gibberellin.

Concentrations of 5 to 500 ppm gibberellin

resulted in an excellent set of enlarged b e rrie s.

A fairly good set was reported

also from the use of one ppm dip, but the c lu sters were straggly, due to a large
number of sm all underdeveloped b e rrie s.

METHODS AND MATERIALS

Introduction: A se rie s of studies was conducted during 1957 and 1958
to determ ine the effects of gibberellin on the straw berry, apple, peach and
cherry, and any p ractical applications that might be derived from the use of
gibberellin. All experim ents were perform ed at E ast Lansing, Michigan,
between January, 1957 and October, 1958. Greenhouse investigations were
conducted in the Michigan State University plant science greenhouses.

Field

studies w ere made on the Michigan State University horticultural farm .

All

plants w ere grown under the naturally occurring photoperiods.
The term gibberellin does not distinguish between the four known chem i­
cally different gibberellin compounds. These gibberellins are m ore a cc u ra ­
tely re fe rre d to as gibberellin A^, A2 , Ag and A^. Gibberellin Ag has also
been re fe rre d to as gibberellin X, and gibberellic acid, with the last term
appearing m ost often in the literature.
Two gibberellin m aterials were used in these investigations. Potassium
gibberellate, the potassium salt of gibberellic acid, was supplied by M erck
and Company, Incorporated, Rahway, New Jersey.

This compound is often

abbreviated GA and this abbreviation has been used in certain tables in this
thesis.

The other gibberellin compound was a m ixture of gibberellin A^ and

A^, furnished by the C harles Pfizer Company, Brooklyn, New York.

Biological

24.

activity of both gibberellins appeared to be sim ilar.
F o liar applications of a known concentration of gibberellin were em ­
ployed in the field investigations.

In the greenhouse studies, aqueous gibber­

ellin solutions w ere applied to the apex or young expanding leaf of a plant
with a m icropipette.

This made it possible to apply a m easured amount of

gibberellin to each individual plant.
Whenever possible data were subjected to an analysis of variance. A
com parison of treatm ent means at the 5 percent level was perform ed using
the multiple range test as advocated by Duncan (1955), and the resu lts ex­
p resse d accordingly. When one and two values w ere m issing in a randomized
block design, the m issing values were calculated according to methods des­
cribed by Snedecor (1957). Form ulae derived by Baten (1939) were used to
calculate three m issing numbers.
Effect of Gibberellin on the Straw berry (F ragaria spp. ):

Robinson

straw berry plants w ere potted in 6-inch clay pots and placed on a bench in
the greenhouse on February 8 and 12, 1957. Plants were treated on February
17 with 10, 50 o r 100 m icrogram s of gibberellin p er plant, applied with a
m icropipette to the shoot apex to determine if straw berry plants would ex­
hibit any response to applications of gibberellin.

Each treatm ent included

18 replications of three plants p e r replication, and 54 non-treated plants
served as controls.

The length of the petioles of the new leaves was m easured M arch 5,
1957. The number of visible scapes was counted and m easured, and the
number of opened flowers were recorded on M arch 7. The length of the elon­
gated crown was m easured on April 4. The number and weight of all fruit
produced was recorded at periodic intervals from April 5 to April 22, 1957.
The potted plants w ere placed on a th ree -tiere d bench on April 22,
1957. Runners w ere allowed to hang over the side of the pots and develop
accordingly.

The length of the runner between the m other plant and first

runner plant, and between subsequent runner plants was m easured on June 8,
1957, to determ ine the effect of the applications of gibberellin on runner
elongation.
A study was conducted in the greenhouse in the fall of 1957 to d e te r­
mine if Robinson straw berry plants, which had not been subjected to an ex­
tended period of freezing tem peratures, could be stim ulated to develop m ore
rapidly through applications of gibberellin. Runner plants, which had devel­
oped during the sum m er, w ere dug, potted in 6-inch clay pots and placed on
a bench in the greenhouse on October 14, 1957. These plants w ere removed
from non-treated plots and plots that had received one to four applications
of gibberellin in the field between April 28 and July 7, 1957, and were m ain­
tained in separate groups according to their previous treatm ents.

All the

leaves and a portion of the root system were pruned from each plant p rio r to

potting.

Ten plants in each group w ere treated with 100 m icrogram s of

gibberellin on October 20, and ten plants in each group kept for controls.
Periodic reco rd s w ere kept on the number of leaves p e r plant develop­
ing from October 29 to December 30, 1957 to determine if the treatm ents
hastened the vegetative development of the plant. Data were also taken on
the visible appearance of the peduncle, the number of flowers that developed,
and the percent fruit set.

The percent fruit set was calculated on the basis

of the number of norm ally developed fruit, and did not include any distorted
fruit.
There is a relationship between the time of rooting of the straw berry
runner plant and the number of flowers that it will produce (Schilletter and
Rickey, 1929). An investigation was perform ed in the greenhouse during the
fall and winter of 1957-58 using the firs t five runner plants to develop on the
stolon, to determ ine if the flower and fruit development for the different
se rie s of runner plants would be affected differently by gibberellin. Robinson
straw berry runner plants w ere dug in the field November 23, 1957 and se p ar­
ated according to their sequence of development on the runners.

The plants

used w ere the first, second, third and fourth runner plants to develop on the
runner.

These plants w ere potted in 6-inch clay pots and placed on a bench

in the greenhouse November 24 in a randomized block design. The follow­
ing treatm ents w ere used:
(a) Control.

(b) 100 m icrogram s of gibberellin applied to the crowns November
27, 1957.
(c) 100 m icrogram s of gibberellin applied to the crowns December
16, 1957.
(d) 100 m icrogram s of gibberellin applied to the crowns January
11, 1958. .
(e) 100 m icrogram s of gibberellin applied to the crowns December
16, 1957, and again on January 11, 1958.
Each treatm ent included ten replicated plants for each group of runner plants.
A number of the flowers in both the treated and non-treated plants w ere
em asculated on January 9 and 10, 1958, so that pollen viability might be
evaluated. Pollen from flowers on the treated plants was placed on the stig­
m as of em asculated flowers of non-treated plants, and pollen from flowers
on the control plants was placed on the em asculated flowers of the plants
treated with gibberellin. Other flowers of both treated and non-treated plants
w ere brushed with a cam el’s hair brush to insure self-pollination. Pollen
from several p rim ary flowers of the various treatm ents was stained with
acetocarm ine solution to determ ine viability.
The total number of flowers produced p e r plant was recorded F ebruary
19, 1958, and the number of fruit, both norm al and abnormal, was counted
M arch 4.

The effect of a lower concentration of gibberellin was also evaluated in
the greenhouse. Robinson straw berry plants, dug in the field in November,
w ere potted in 6-inch clay pots and placed on a bench in the greenhouse on
November 27, 1957. All the m ature leaves and a portion of the roots w ere
pruned off each plant and the plants treated November 27 with 1, 10, 50 or
100 m icrogram s gibberellin applied to the crown. A randomized block de­
sign was used and included 12 replicated plants for each treatm ent and 12
replicated non-treated plants.
The length of two petioles p er plant and the peduncle was m easured
F ebruary 14, 1958. Pollen from some of the p rim ary flowers of both the
non-treated and the treated straw berry plants was stained with acetocarm ine
February 15. The number of flowers p er plant was recorded February 19,
and the number of fruit counted on F ebruary 28, 1958.
An investigation to evaluate the effect of applications of higher concen­
trations of gibberellin was conducted in the greenhouse in 1958. Robinson
straw berry plants that had been dug in the field in November, 1957, and
kept in cold storage at 0“ C, w ere potted in 6-inch clay pots and placed on a
bench in the greenhouse on February 12, 1958. A randomized block design
was employed with eight plants p e r treatm ent.

T reatm ents included a con­

tro l and applications of 100, 500 or 1, 000 m icrogram s gibberellin p e r plant,
which w ere applied to a young developing leaf on M arch 14, 1958.

R ecords of petiole length, peduncle length, flower number, and crown
elongation w ere taken April 27, 1958. The number of runners, length of
runners, and distance between runner plants were recorded on May 18. The
crown diam eter at the base of the crown was m easured May 24, using a v e r­
nier caliper.
Robinson straw berry plants were obtained from a com m ercial nursery
on M arch 14, 1958. Some of these plants were placed in cold storage at 0°C
for later investigations, and others were potted in 6 -inch clay pots and
placed on a bench in the greenhouse on M arch 15. The plants were treated
with 1, 10, 100, 500 or 1, 000 m icrogram s of gibberellin on M arch 27. The
aqueous gibberellin solution was applied to a young expanding leaf. A random ized block design was used, with eight replicated plants p e r treatm ent, and
eight non-treated plants.
Flowers were brushed with a cam el’s hair brush to provide pollination.
Petiole length, peduncle length and length of crown elongation w ere m easured
May 16. The number of runners, flowers, and fruits was also counted.

On

May 24, 1958, the length of the pedicel of the p rim ary flower was m easured,
the number of runners counted, and the diam eter of the crown m easured.
The length of runners, number of runner plants, and distance between runner
plants was also recorded.
The previous experim ent was repeated and in addition, a modification

of the procedure described by Nitsch (1950), using lanolin paste applications
of plant growth regulators on straw berry fruits, was employed to observe
the effects on fruit development on the plants treated with gibberellin. Plants
which had been kept in cold storage since M arch 14, 1958 were potted in 6inch clay pots and placed in the greenhouse on April 2, 1958, and treated
with gibberellin on April 9. Data were taken on the rate of flower opening
from April 23 to May 12, 1958. Flowers were brushed with a cam el's hair
brush at periodic intervals to facilitate pollination.

Certain flowers on the

treated plants w ere coated with a lanolin paste containing one percent indolebutyric acid on May 10.

Certain other flowers were treated likewise with a

one percent lanolin paste m ixture of gibberellin on May 11, 1958.
M easurem ents of crown diam eter, crown elongation, and petiole length
w ere made on June 3. The number of runners and flowers was also recorded.
Peduncle and pedicel lengths were m easured June 5, 1958, when an evaluation
was made,of the effect of all treatm ents on fruit set and development.
The above experim ent was repeated using plants started in the green­
house on April 9, 1958.

The initial gibberellin treatm ents were applied

A pril 15 to a young expanding leaf on each plant. Records were taken on
rate of flower opening from May 1 to May 23. The flowers were coated with
a lanolin paste containing either one percent indolebutyric acid o r gibberellin
on May 11, approxim ately six days after they had bloomed.

Data on the

plant development, as affected by applications of gibberellin, w ere taken
June 4 and 5, 1958.
The translocation of the gibberellin stimulus in the straw berry stolon
was investigated.

Robinson plants w ere started in the greenhouse on February

8, 1957, and one runner was perm itted to develop on each plant and to form
runner plants.

In 18 plants the firs t and second runner plants were potted in

3-inch clay pots, and the rem ainder of each runner and subsequent runner
plants hung over the side of the bench.

The runner plants of the other 18

plants w ere not potted to prevent rooting.

One June 24, 1957, 100 m icrogram s

of gibberellin w ere applied to a m ature leaf of each of the first runner plants
of six rooted and six non-rooted runner plants.

Six of the second runner

plants in each group were treated sim ilarly. The runner plants of six plants
in each group were not treated. The length of the petioles of the mother
plant and firs t two runner plants on each runner were m easured July 28 and
August 10, 1957.
This experim ent was repeated in 1958 with a few modifications.
Robinson straw berry plants w ere started in the greenhouse on M arch 15, 1958,
and one runner was perm itted to develop on each plant. The plants were di­
vided into two groups in June, and the first two runner plants in the first
group w ere potted in 6 -inch clay plots.
w ere not potted to prevent rooting.

The runner plants in the second group

The plants received the following tre a t-

merits on July 9, 1958:
(a) Control.
(b) 500 m icrogram s of gibberellin applied to a m ature leaf of the
firs t runner plant.
(c) 500 m icrogram s of gibberellin applied to a m ature leaf of the
second runner plant.
(d) 500 m icrogram s of gibberellin applied to the node on the run­
ner between the first and second runner plants.
(e) 500 m icrogram s of gibberellin applied directly to the runner
between the first runner plant and the next distant node.
Each treatm ent contained eight replicated plants for the non-potted
runner plant group, and eight replicated plants for the potted runner plants.
The length of two petioles on the m other plants and first and second runner
plants was m easured August 20, 1958.
Cats kill straw berry plants were dug on April 19, 1958, and potted in
8-inch clay pots. They were placed on a bench in the greenhouse and divided
into two groups in July. The runner plants were handled in the same m anner
as described above for the Robinson runner plants.

The plants were treated

sim ilarly also with 500 m icrogram s of gibberellin on August 1. Petiole
m easurem ents w ere taken August 21, 1958 on the m other plants and firs t
and second runner plants. Two petioles on each plant were m easured, and

m easurem ents subjected to an analysis of variance to determ ine if differences
existed between treatm ents for the individual m other plants and the runner
plants.
Portions of rows of year old straw berry plants growing in the Michigan
State U niversity H orticultural Department variety testing plots were sprayed
with a foliar application of 100 ppm gibberellin on April 29, 1957 to d eter­
mine if different straw berry varieties would respond sim ilarly to applications
of gibberellin. V arieties treated included Robinson, Catskill, Prem ier,
Tennessee Beauty, Red Crop, Crimson Flame, M 1322 and Pocahontas.

The

scapes w ere visible, but the plants w ere not in full bloom at this time.

The

distance from the base of the peduncle to the calyx of the prim ary flower was
m easured on May 26. Fifty peduncles w ere m easured for each variety in both
the treated and non-treated portions of the rows.
The treated row portions of Robinson, Catskill and P rem ier m easured
20 feet.

The yield of fruit for both the treated and non-treated plants was ob­

tained from June 15 to June 29, 1957.
The effect of applications of gibberellin on straw berry plants was also
investigated under field conditions. On April 23, 1957 one row each of Catskill
and P rem ier straw berry plants were planted on the Michigan State University
horticultural farm .

The rows w ere 90 feet long and three feet apart, and the

plants w ere set approxim ately 18 inches apart in the row. Two rows of

Robinson and an additional row of both Catskill and P rem ier were planted on
A pril 28. The planting was divided into ten equal plots.

Each plot contained

two rows of each of the varieties with six plants in each row.
T reated plots received foliar applications of gibberellin at 100 ppm on
the dates specified in Table I. All blossom buds were removed on May 14
and as they appeared th ereafter during the growing season.
The runners on all the plants w ere counted on June 25 or June 29, 1957.
Two average plants in each row in each plot w ere selected on June 30, and
m easurem ents made of all th eir runners. The number of runners on these
selected plants was counted August 17, 1957, and any elongation of the crown
on these plants was recorded.
On May 4, 1958, three entire rows, one of each variety, were sprayed
with 100 ppm of gibberellin. This application was made irrespective of the
previous season's treatm ents.

The m aterial was applied before any inflores­

cences w ere visible, and two weeks before full bloom occurred.

F ru it was

harvested from all plots between June 12 and July 14, 1958.
Effect of Gibberellin on the Apple (Pyrus Malus L .)
The effect of applications of gibberellin on the shoot growth of rooted
E ast Mailing cuttings was investigated in the greenhouse in 1957. Rooted
Mailing IX and XVI cuttings were potted in 6-inch clay pots on January 28, 1957
and the potted plants randomized on a bench in the greenhouse. The Mailing IX

35.

TABLE I
Plot Design for Field Study of Effects of Foliar Applications of Gibberellin
on Robinson, P rem ier and Catskill Straw berry Plants, Showing Plots
Which Received the Applications of Gibberellin and the Dates
of the Applications in 1957.
Plot

GA (ppm)

Date of Application

I

100

II

0

III

100

IV

100

April 28

100

April 28, May 30,

July 7

April 28, May 30,

July 7

V

.

VI

0

VII

100

VIII

0

IX

100

X

0

April 28, May 30, June 8, July 7

July 7

April 28, May 30

cuttings w ere treated with 10, 50 and 100 m icrogram s of gibberellin p e r
plant on February 2, 1957. Each treatm ent included three replicated plants,
and th ree non-treated plants were used as controls. The Mailing XVI cut­
tings w ere treated sim ilarly on February 14.
Shoot growth on all cuttings was m easured M arch 18. The appli­
cations of gibberellin were repeated M arch 20, and subsequent shoot m eas­
urem ents made April 1, 9 and 19, 1957.
An investigation was made of the number of applications of gibberellin
and the tim e interval between applications on the vegetative growth of rooted
Mailing cuttings.

Rooted Mailing IX and XII cuttings w ere potted in 8-inch

clay pots and placed on a greenhouse bench on May 20, 1957. These cuttings
w ere pruned on June 1 to one shoot p er plant, and the diam eter of the cut­
tings m easured imm ediately below this shoot. Plants w ere then subjected
to the following treatm ents:
(a) control.
(b) 100 ppm gibberellin weekly.
(c) 100 ppm gibberellin at two week intervals.
(d) 100 ppm gibberellin every four weeks.
Each treatm ent consisted of three replications of four plants p er replication
for each Mailing selection.

The gibberellin was applied as a foliar application,

and contained a very sm all amount of Tide* as a wetting agent.
*T rade m ark of detergent m anufactured by Proctor and Gamble Company.

Shoot length was m easured June 23, August 16 and September 28, 1957.
D iam eter m easurem ents were also taken September 28, at which time the
investigation was discontinued.
Individual m ature bearing apple tre e s of Jonathan, Delicious, McIntosh,
G rim es Golden and Wealthy varieties w ere treated in the spring of 1957 to
evaluate the effect of gibberellin on fruit set and development.

Two branches

w ere selected on each tree to which foliar applications of 10 and 100 ppm of
gibberellin w ere applied May 9. A third branch of each tree was selected
as a control.

The tre e s were in full bloom when treated. The number of

fruit p e rsistin g on the respective branches was counted on August 17, 1957.
One-half of individual m ature bearing Jonathan, McIntosh, Northern
Spy and Wealthy apple tre e s received foliar applications of gibberellin at 100
ppm on May 28, 1957. This application was made approximately 20 days
afte r full bloom to observe the influence of gibberellin on fruit and shoot
development.
Effect of Gibberellin on the Cherry (Prunus Ce rasu s L. and
Prunus Mahaleb L .)
Shoot Growth:

Seedling Mahaleb cherry trees, which had been dug

in the field in the fall of 1956 and stored in a cold storage at 0*C, were potted
in 6-inch clay pots on January 17, 1957, and placed on a greenhouse bench.
All tre e s w ere pruned to eight inches in height. Applications of 10, 50 or

100 m icrogram s of gibberellin p er plant were applied to the term inal bud
on F ebruary 2.
replication.

Each treatm ent included nine replications of three tre e s per

Twenty-seven tree s were left as controls. The length of all

developing shoots was m easured April 6 and 27, 1957.
In a second investigation, 28 one-year-old Montmorency cherry tre e s
were obtained from a com m ercial nursery in March, 1958. They were
potted in silica sand in 12-inch clay pots and placed in the greenhouse on
M arch 29, 1958. F re sh weight determ inations were made p rio r to potting
so that the effect of gibberellin on any increase in plant weight could be cal­
culated.

The nutritional level of the tre e s was maintained with three appli­

cations p e r week of a standard Hoagland solution. The sand was flushed
with tap w ater about once every two weeks to prevent localization of salts.
By May 21, all but three of the tre e s had set term inal buds. At this
tim e all tre e s were randomized as four groups of seven tre e s each.

Three

groups received foliar applications of 100, 500 or 1, 000 ppm gibberellin,
respectively, and a non-treated fourth group was used as a control.
w ere pruned to three lateral branches.

The tre e s

Trunk diam eter was m easured six

inches above the graft union.
Periodic m easurem ents of all shoot elongation w ere made from May
21 to July 3, 1958, when it was noted that all the tre e s had again formed
term inal buds.

On July 11, 1958 the tre e s were again sprayed with the same

concentrations of gibberellin that they had received on May 21. A final r e ­
cord of all shoot growth and of trunk diam eter was taken on August 20, 1958.
Six tre e s from each treatm ent were then harvested to determ ine the fresh
and dry weights of the tops and the roots.

The graft union was used as a

dividing line between the top and the root.

Top and root dry weights were

obtained by drying the tops and roots to a constant weight in an oven at 72°C.
Flowering and Fruiting:

Single branches on six individual m ature

Montmorency cherry tre e s were selected to be used in an evaluation of the
effect of applications of gibberellin on fruit set of sour ch erries.

Branches

received foliar applications of 10 and 100 ppm gibberellin on May 2, 1957.
The tre e s w ere in full bloom at this tim e.

F ruit p ersistin g on the branches

was counted July 6, 1957.
A foliar application of gibberellin at 100 ppm was applied to two
m ature bearing Montmorency cherry tre e s on May 28, 1957, to ascertain
whether the m aterial might have an effect on the size of developing fruits.
This was slightly m ore than three weeks after full bloom and both tre e s were
bearing a crop of fruit.
Effect of Gibberellin on the Peach (Prunus P ersica Batsch.)
Stimulation of Seedling Growth:

E lberta peach seeds, which had p r e ­

viously been subjected to stratification, were potted in 4 -inch clay pots and
placed on a bench in the greenhouse on February 5, 1957. Following g e r­

mination, they w ere treated on February 16, with 10, 50 and 100 m icro ­
gram s of gibberellin p e r plant.

Each treatm ent included ten replicated

plants in a random ized block design, and ten non-treated plants w ere used
as a control.
Plant height was m easured March 18, 1957, and on M arch 20, the
plants w ere again treated with gibberellin at the same concentrations as
initially applied. M easurem ents of shoot elongation were made on April
2, 9 and 19, 1957.
Flowering and Fruiting:

T hree branches of each of six individual

m ature Halehaven peach tre e s were selected to be used in an evaluation
of the effect of gibberellin on fruit set of peaches. Two branches received
foliar applications of 10 o r 100 ppm of gibberellin on May 2, 1957, the third
branch being used as a control.

Sprays w ere applied when tre e s were in

full bloom. The number of fruits persistin g on the tre e s was counted on
July 13, 1957.
One-half portions of two m ature bearing Redhaven peach tre e s r e ­
ceived a foliar application of gibberellin at 100 ppm on May 28, 1957 to
determ ine if such an application would enhance fruit size and rate of develop­
ment.

This was three and one-half weeks after full bloom, and the tre e s

w ere bearing a full crop of fruit.

H alf-tree portions of six m ature Halehaven tre e s received a foliar
application of 1, 000 ppm gibberellin on July 20, 1957 to determ ine if shoot
growth could be stimulated, and fruit size increased. This was two and
one-half months afte r full bloom, and approximately one month before
fru it ripening.

These tre e s had been used e a rlie r in the season for in­

vestigating the effect of gibberellin on fruit set.

The selection of the

h a lf-tree s to be treated was made irrespective of their previous tre a t­
m ents.

RESULTS

Straw berry Response to Applications of Gibberellin

Robinson straw berry plants started in the greenhouse on February 8
and treated with gibberellin February 17 produced visible response to the
gibberellin treatm ents within two weeks.

Data presented in Table II indicate

the effect of gibberellin on petiole length, peduncle length, crown elongation,
and flower and fruit development. A statistical analysis indicated that plants
in all the gibberellin treatm ents produced petioles that were significantly
longer than petioles on the control plants. While peduncles were not p ro ­
duced in all plants, the peduncles produced by the treated plants were
m arkedly ta lle r than peduncles on the non-treated plants.
The number of flowers in bloom on M arch 14 was g re a te r in the
treated plants (Table II). This was interpreted as an indication of e a rlie r
flowering following treatm ent with gibberellin. The number of fruit h a r­
vested, expressed on a percent basis, was slightly less for the treated
plants (Table II). However, the weight p er fruit was m arkedly lighter in
the treated plants; the b erry weight decreasing as the concentration of
gibberellin applied increased (Table II).
T reatm ents of 50 and 100 m icrogram s of gibberellin p er plant r e ­
sulted in an internodal elongation between the petioles.

This caused the

TABLE II
The Effect of Gibberellin on the Petiole Length, Peduncle Length, Crown
Elongation, Flowers p e r Peduncle, and F ruit of Robinson Straw­
b e rry Plants. Plants T reated February 17, 1957.

Observation

M icrogram s GA p er Plant
50
100
10

Date

0

Petiole length (cm)

M arch 5

5. 3

7.7

10.2

10.2*

Peduncle length (cm)

M arch 7

1.4

5.8

12.6

10.2

Crown elongation (cm)

April 4

--

0.1

5.6

9.3

Flow ers p e r Peduncle

M arch 14

2.5

2.9

4.2

3.9

F ru it p e r Plant

April 5-22

1.2

0.8

1.0

0.9

4.8

3.9

2.0

1.0

Weight p e r F ru it (gm)

*Observation analyzed statistically. The various gibberellin treatm ents
not underscored by a common line differ significantly at the 5 percent
level.

crowns of treated plants to erupt from th eir norm al rosette pattern of
growth and extend vertically as a stem (Table II, and Figures 1 and 2).
The extended crown lacked sufficient strength to rem ain e rect and grew
in a horizontal plane as it continued to elongate.
As the effect of the applications of gibberellin was dissipated, the
crown resum ed its norm al rosette-type of growth with shorter leaf petioles.
This rosette-type crown formed roots when it established contact with the
f

soil.
Plants treated with 50 and 100 m icrogram s of gibberellin are com­
p ared with a non-treated plant in Figure 3. It can be observed that while
treated plants produced longer petioles and peduncles than the control plants,
th ere was essentially little difference between the 50 and 100 m icrogram
treatm en ts. Peduncle elongation was increased m ore than petiole elonga­
tion, which resulted in the peduncles extending above the leaves.
The norm al pattern of fruit development was not observed on all
plants treated with 50 and 100 m icrogram s of gibberellin.
many of the fruits did not develop.

The achenes on

Receptacular tissue of these flowers in

the a re a supporting the p istils did not swell, and the non-functioning achenes
rem ained appressed on the non-expanded receptacles.

The torus of these

flowers, just above the calyx and beneath the area of appressed achenes,
expanded slightly two to three weeks after anthesis and colored at the

Figure 1
Crown elongation of Robinson straw berry plant treated with 50
m icro gram s gibberellin on F ebruary 17, and photographed on A pril
18, 1957.

Figure 2
Crown elongation of plant receiving 100 m icrogram s gibberellin
on February 17, and photographed on April 18, 1957.
Note how distant portion of crown has started to resum e a ro se tte
appearance with shortened petioles.

45.

corresponding tim e when the fruit of non-treated plants ripened.

F ru it

from treated plants is compared with fruit from non-treated plants in
F igure 4.
Data do not accurately illustrate the effect of gibberellin on runner
development. This was complicated because not all plants produced an
inflorescence and fruit.

Flowering and fruiting tend to delay runner fo r­

m ation so that plants not fruiting probably would initiate runners e a rlie r
and produce them m ore abundantly. Photoperiod probably exerted an in­
fluence also, since runner form ation has been reported to occur under 14
hours of light in a 24 hour cycle (Hartmann, 1947). Figure 5 shows the
p attern of runner form ation in treated and non-treated plants.

Runner

form ation at the nodes of the treated plants appeared to be retarded while
the crown was elongating.
Data presented in Table III indicate that treatm ent with gibberellin
appeared to have an effect on the length of runner development between
runner plants.

The distance between the m other plant and the firs t runner

plant was g re a te r in all treatm ents, as compared to non-treated plants.
However, the distance between subsequently m easured runner plants was
g re a te r in the controls. The only exception occurred between the second
and third runner plants in the 100 m icrogram p e r plant treatm ent.
Robinson straw berry plants, which were dug in the field before

Figure 3
Comparison of Robinson straw berry plants receiving 0, 50 and
100 m icrogram s gibberellin on F ebruary 17, and photographed on
M arch 14, 1957.
Left to right: 0, 100 and 50 m icrogram s gibberellin p e r plant.
Note elongation of petioles and peduncles of treated plants and slight
difference in degree of response between the 50 and 100 m icrogram
applications.

Figure 4
Comparison of fruit from non-treated plants (above) and plants
treated with 100 m icrogram s of gibberellin on F ebruary 17, 1957.
Photographed April 18. T reatm ent resulted in longer pedicels and
abnorm al fruit.

47.

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Figure 5
Comparison of straw berry runner development of non-treated
plant and plant receiving 100 m icrogram s gibberellin on F ebruary 17.
Photographed April 18, 1957.
Top: Plant treated with 100 m icrogram s gibberellin showing elon­
gated crown and a runner developing from each node.

Note reta rd ed

stage of development of runners and runner plants.
Bottom: N on-treated plant exhibiting norm al pattern of plant and
runner development.

Note presence of runner plants.

they had been exposed to an extended period of freezing tem peratures, w ere
placed in the greenhouse October 14 and treated with 100 m icrogram s of
gibberellin on October 29, 1957. The plants were segregated into groups
according to previous sum m er treatm ents of gibberellin.

The number of

leaves p e r plant, developing between October 29 and December 30, 1957
w ere counted and indicated that the gibberellin treatm ent had essentially
no effect on leaf number nor rate of leaf appearance. However, the appli­
cations of gibberellin on October 20 applied to the plants in the greenhouse
resu lted in a m arked difference in flower number and rate of development.
The total number of flowers produced by the treated and control
plants during December and January is illustrated in Figure 6. The percent
of the flowers in bloom at weekly intervals in December is illustrated in
Figure 7. Thus, it is shown that not only were m ore flowers in bloom on
a certain date in the treated plants, but that the percent of the total number
in bloom on a specific date was also g reater for the treated plants.

This

would indicate that plants treated with gibberellin both flowered e a rlie r and
produced m ore flowers p er plant.
The number of flowers p e r peduncle is illustrated in Figure 8 and
presented in Table IV. Observations on all dates revealed m ore flowers
p e r peduncle for treated plants.

While the sum m er applications of gibber­

ellin did not appear to have any effect on flower number, the plots varied

51.

420
Control
399

Gibberellin

357

/

315

273

231

189

147

105

63

*

21
-T ~

2

9

16
December

23

30

21

January

lire 6. Total num ber of flow ers produced by Robinson straw berry plants
treated with 100 m icrogram s GA p e r plant on October 20, 1957.

100
,

Control

1'

Gibberellin

90

80

70

60

50

40

30

20

10

0

9

16
December

23
January

re 7. Percent flow ers in bloom on respective dates of Robinson straw berry
plants treated with 100 m icrogram s GA p er plant on October 20, 1957.

53.

8

Gibberellin

Control
7

6

Number of Flowers per Peduncle

5

4

3

2

1

0

2

9
Decem ber

16

23

30

21

January

Figure 8. Effect of 100 m icrogram s GA p er plant on number of flowers
p e r peduncle of Robinson straw berry. Plants treated October 20, 1957.

TABLE IV
Number of Flow ers and F ruit p er Peduncle and Percent F ru it Set of Robinson Straw­
b e rry Plants T reated with 100 M icrogram s Gibberellin on October 20, 1957.
Plants Placed in Greenhouse Ocrober 14 and F ruit Counted February 5, 1958.
Field
Plot
Number*

No. Summer
Applications
100 ppm GA

II

0

0
100

III

1

IV

Fruit
p er
Peduncle

Percent
F ruit
Set

6.0
7.7

2.3
1.2

38
16

0
100

6. 4
9.7

2.3
1.3

36
13

1

0
100

5.4
8.9

2.0
1.4

37
16

V

3

0
100

5. 8
8.7

3.2
2.7

55
31

IX

2

0
100

5. 5
6.8

1.4
0.7

25
10

0
100

5. 8
8.3

2.2
1.4

38
17

Average of all plots

M icrogram s
GA
October 20

Flowers
per
Peduncle

*Plot num bers correspond to field plot numbers in Table I.

slightly in number of fruit produced p e r flower stalk and percent fruit set
(Table IV). Yields w ere greatest for the plants in plot V and sm allest for
plants in plot IX. In all plots, however, the number of fruit p er peduncle
and percent fruit set was greatest in plants not treated with gibberellin on
October 20, 1957. An average of the data for all plots indicates the percent
set was twice as great in the non-treated plants.

This is slightly misleading,

however, since treated plants produced m ore flowers.

This increase in

flower number and less fruit p e r plant would tend to give a much lower p e r ­
cent fruit set.

Some abnorm al fruits were observed somewhat sim ilar to

abnorm alities observed for treated plants in the previous greenhouse inves­
tigation.
A few plants from each plot were observed to have developed several
runners.

This phenomena, however, occurred only on plants treated with

gibberellin after being tran sfe rred into the greenhouse.
Runner plants tra n sfe rre d from the field to the greenhouse November
24, 1957 w ere treated with 100 m icrogram s of gibberellin either November
27, Decem ber 16, January 11, or both December 16 and January 11. Pollen
from treated plants was stained with acetocarm ine and the m ajority of the
pollen stained light pink, indicating viability. However, some pollen grains
w ere collapsed and failed to stain.

N on-treated flowers w ere em asculated

and pollinated with pollen from treated flowers, and generally produced

norm al fruit.

T reated flowers em asculated and pollinated with pollen from

n on-treated flow ers generally did not form fruit.

However, a few of such

trea te d flowers did yield normal fruit.
The number of flowers and fruit p e r plant, percent fruit set and p e r­
cent of flow ers yielding abnormal fruit for treated and non-treated plants
for each group of runner plants a re presented in Table V. The number of
flowers p e r plant may or may not have been affected by treatm ent with gib­
berellin.

Since a number of flowers were removed for pollen viability evalu­

ation experim ents before flower num bers were recorded, a comparison would
probably not be valid because, of necessity, m ore non-treated flowers w ere
removed.

In general, all treatm ents resulted in less fruit p e r plant and a

decreased percent fruit set. The treatm ent of January 11, applied when the
plants were in bloom, had less effect on fruit set than any other treatm ent.
Plants treated both Decem ber 16 and January 11 yielded the sm allest amount
of fruit and the g reatest percentage of abnormal fruit, in which the receptacle
supporting the p istils failed to develop. While plants treated on November 27
yielded a high percent of abnormal fruit, they also produced a considerable
yield of norm al fruit.
In an experim ent designed to evaluate the effect of a lower concen­
tratio n of gibberellin, straw berry plants were tran sfe rred from a field plant­
ing to the greenhouse on November 25, 1957, and treated with 1, 10, 50 o r

TABLE V
Effect of Gibberellin on Number of Flowers and F ruit p e r Plant, Percent F ru it Set,
and Percent of Flow ers Yielding Abnormal F ruit of Robinson Straw berry Plants.
Plants Started in Greenhouse November 24, 1957 and T reated with 100 M icro­
gram s of G ibberellin on November 27, December 16, January 11, and
both December 16 and January 11.
Runner
Plant

F ruit
p e r Plant

F ruit Set
(Percent)

6.9
6.1
8.5
7.1
7.2

2.6
2.4
2.9
3.3
2.8

37.8
40.0
34.1
45.6
38.7

0.0
0.0
0.0
0.0
0.0

November 27

11.0
8.4
8.2
; 6.8
8.6

2.4
2.2
1.4
1.2
1.8

21.8
26.2
17.1
17.6
20.9

20.9
17.9
12.2
16.2
17.2

December 16

17.1
12.1
9.6
7.9
11.9

1.3
1.0
1.8
1.0
1.3

7.6
8.3
18.8
12.7
10.9

1.2
14.1
10.4
6. 4
7.3

7.6
8.1
9.1
5.0
7.9

1.0
1.8
3.0
0. 5
1.8

14. 7
22.2
33.0
10.0
23.1

4.4
6.2
7.7
0.0
5.8

11.4
11.9
9.6
9.6
10.6

0.2
0.9
1.3
1.3
0.9

1. 8
7.6
13. 5
13. 5
8.7

29.8
20.2
25.0
26.0
25.2

Date T reated

Control

1st
2nd
3rd
4th
Average for T reatm ent
1st
2nd
3rd
4th
Average for T reatm ent
1st
2nd
3rd
4th
Average for T reatm ent'
January 11

1st
2nd
3rd
4th
Average for T reatm ent
Decem ber 16 and
January 11

1st
2nd
3rd
4th
Average for T reatm ents

Flowers
p e r Plant

Flowers Produc­
ing Abnormal
F ruit (Percent)

100 m icrogram s of gibberellin p e r plant on November 27. Plant responses
to these applications a re presented in Table VI. Plants which received only
one m icrogram of gibberellin did not differ from the controls in any o b ser­
vations. Petioles and peduncles were significantly longer on plants treated
with 10, 50 o r 100 m icrogram s of gibberellin. Plants receiving applications
of 10 and 50 m icrogram s of gibberellin p e r plant appear to have produced
m ore flow ers than the control plants. This may not be a valid analysis,
since some blossom s w ere removed from the control plants and plants
treated with 50 and 100 m icrogram s of gibberellin for pollination studies.
The percent fru it set of normal b e rrie s was relatively the same for all
treatm ents, except plants treated with 100 m icrogram s of gibberellin, which
yielded a considerable lower percent of norm al fruit. Abnormal fruits were
also produced on plants treated with 50 or 100 m icrogram s of gibberellin.
Figure 9 com pares a representative plant from each treatm ent.
The elongation response of the petioles and peduncles to the gibberellin
concentrations is plotted in Figure 10. One can observe that the response of
the peduncles to applications of gibberellin is accentuated over a wider range
of concentrations than occurred in the petioles.

T here was only a slight in­

cre ase in the petiole elongation at the concentrations of gibberellin g reater
than 10 m icrogram s, while the peduncles continued to exhibit a m arked r e ­
sponse to the 50 and 100 m icrogram applications.

TABLE VI
Effect of Applications of Gibberellin on Petiole Length, Peduncle Length,
Number of Flow ers per Plant, and F ru it Development of Robinson
Straw berry Plants. Plants Potted in Greenhouse November 25,
1957 and T reated November 27.
Observation

Date

0

M icrogram s GA p e r Plant
1
10
50

100

Petiole length (cm)

February 14

4.1

4.8

7.3

8.5

9. 7*

Peduncle length (cm)

February 14

5.3

5.5

12.1

17.3

19. 9*

F ru it set (percent)

F ebruary 28

29.9

34.8

37.6

26.7

17.5

--

--

0.7

5.3

30.9

0

1

6.8

8.3

Abnormal fruit (p er­
February 28
cent)

Flow ers p e r plant

February 19

100
8.8

50

10

10.9

11.8*

* Observations analyzed statistically. The various gibberellin treatm ents
not underscored by a common line differ significantly at the 5 percent
level.

60.

ui qjSusq

C ertain flowers in each treatm ent w ere emasculated and treated with
pollen from non-treated plants, or plants that had received 50 or 100 m icro gram s of gibberellin. Em asculated flowers on the non-treated plants p ro ­
duced fruit irrespective of their pollen source. All em asculated flowers on
plants treated with one and 100 m icrogram s of gibberellin that received
pollen from non-treated plants failed to set fruit. The m ajority of em as­
culated flow ers on plants treated with 10 m icrogram s of gibberellin and
pollinated with non-treated pollen produced normal b e rrie s.

Sim ilarly

treated flowers on plants treated with 50 m icrogram s of gibberellin and
pollinated with pollen from non-treated plants generally did not yield fruit.
Pollen stained with acetocarm ine appeared to be viable.
Robinson straw berry plants held in cold storage at 0°C from Novem­
b er 24 to F ebruary 12, and then potted and placed on a greenhouse bench,
w ere treated with 100, 500 and 1, 000 m icrogram s of gibberellin per plant
on M arch 14, 1958. Data presented in Table VII indicates the response of
the plants to these treatm ents.

Both petiole and peduncle length w ere in­

creased by all applications, the lengths becoming increasingly g reater with
increasing concentrations of gibberellin. Flower number appeared to be r e ­
duced on treated plants and the percent fruit set reduced to nil for plants
treated with 500 and 1, 000 m icrogram s of gibberellin. While plants treated
with 500 and 1, 000 m icrogram s of gibberellin yielded no fruit, over 60 p e r ­
cent of the flowers produced abnorm al fruit.

TABLE VII
Effect of Applications of Gibberellin on the Petiole and Peduncle Length,
Grown Elongation and Diameter, Flower Number and Development,
and Runners p er Plant of Robinson Straw berry Plants Started
in Greenhouse February 12, and T reated M arch 14, 1958.
Observation

Date

M icrogram s GA p er Plant
0

100

500

1, 000

Petiole length (cm)

April 27

8.0

9.9

15.0

1.6.9*

Peduncle length (cm)

April 27

7.0

9.1

14.0

18.4

Flow ers p er plant

April 27

7.4

5.0

4.0

5.6

44.0

10.0

0.0

0.0

0.0

43.3

66.7

61.5

3.6

29.6

38.1

F ru it set (percent)
Abnormal fruit (p er­
cent)

April 27

Crown elongation

April 27

Crown diam eter

May 24

10. 8

9.6

5.7

6. 6*

Runners p e r plant

May 18

4.3

4.3

3.0

4.0

Average runner
length (cm)

May 18

29.6

60. 5

41.2

40.9

Runner plants p e r
m other plant

May 18

1.3

3.4

1.3

2.0

* Observations analyzed statistically. The various gibberellin treatm ents
not underscored by a common line differ significantly at the 5 percent
level.

Crown elongation was m arkedly increased through the 500 and 1, 000
m icrogram applications of gibberellin. A significant reduction in crown
diam eter was also observed with these two treatm ents.

While the runner

num ber p e r plant did not appear to be affected by treatm ent with gibberellin,
the average runner length was longer on treated plants. The distance between
the m other plant and firs t runner plant was 37. 8, 42. 2 and 40. 5 centim eters,
respectively, for the 100, 500 and 1, 000 gibberellin-treated plants, as com­
p ared to 31.1 centim eters for the non-treated plants.
Robinson straw berry plants which w ere started in the greenhouse
M arch 15, 1958, w ere treated with gibberellin at 1, 10, 100, 500 and 1, 000
m icrogram s p er plant on M arch 27. Observations on plant development as
affected by various treatm ents are presented in Table VIII. Significant in­
cre ases in petiole length were obtained with applications of 500 and 1, 000
m icrogram s gibberellin only. While all treatm ents except the one m icrogram
application resulted in longer peduncles, only 10, 500 and 1, 000 m icrogram s
gibberellin-treated plants produced longer pedicels on the prim ary flower.
Flow ers w ere brushed with a cam el's hair brush when in bloom to insure
tra n sfe r of pollen to the stigm a.

The number of flowers p e r plant was sim ilar

for all treatm ents, but the percent fruit set was markedly reduced or inhibited
by the 100, 500 and 1, 000 m icrogram applications. Abnormal fruit were
form ed in all gibberellin treatm ents, the percentage increasing greatly at the
higher concentrations.

TABLE VIII
Effect of F o liar Applications of Gibberellin on the Vegetative and F loral De­
velopment of Robinson Straw berry Plants. Plants Started in Greenhouse
M arch 15, 1958, and T reated with Gibberellin M arch 27.
M icrogram s Gibberellin p er Plant
1
10
100
500 1,000

Observation

Date

Petiole length

May 16

9.8

10.0

Flow ers p e r plant

May 16

8.1

9.6

Abnormal fruit (per­
cent)

May 16

0.0

0. 3

27.7

33. 7

37.7

Crown elongation (cm) May 16

0.0

0.0

0.0

Crown diam eter (mm) May 24

12.3

12.5

Runners p e r plant

May 24

3.0

3.3

Runner length

May 24

42.0

42. 5

Runner plants (ave.)

May 24

2.1

1.9

Runner length m other
plant to 1st runner
plant

May 24

36.8

36.8

0

1

7.8

F ru it set (percent)**

Peduncle length (cm)

Pedicel length (cm)

May 16

May 24

0

11.5 11.4

13. 7

12. 9*

8.0

7.5

8.0*

13.2 23.4

44.2

57.8

9.4

0.0

0.0

2.0

43.0

45.6

12.4 11.2

8.2

6.8*

3.5

3.6

2.3

56.1 54. 9

34.2

28.5

2. 6

0.3

0.5

41.8 43.2

39.5

36.8

1 00

1000

500

8.8

13.4 16.3

18.3

22. 3*

0

1

100

10

1000

500

2 .9

3.4

4 .0

3.9

4. 3*

9.0

3.5

3.4

10

3.5

* Observations analyzed statistically. Values of various gibberellin
treatm ents not underscored by a common line differ significantly at
the 5 percent level.
F ruit norm al in appearance possessing enlarged achenes and receptacular tissue with no distortion in calyx region.

Crown elongation was produced by plants treated with 100, 500 and
1, 000 m icrogram s of gibberellin, and crown diam eter was significantly r e ­
duced on plants receiving 500 and 1, 000 m icrogram s of gibberellin. The
number of runners p e r plant was relatively consistent in all treatm ents. The
runner length and number of runner plants p er mother plant were greatest
for the 10 and 100 m icrogram treatm ents, and least for the 500 and 1, 000
m icrogram applications.
A repetition of the previous experiment, with plants started in the
greenhouse April 12 and treated April 19, produced sim ilar resu lts (Table IX).
The lower gibberellin concentrations, one and 10 m icrogram s, produced
slightly longer peduncles and a g rea ter percentage of abnormal fruit than in
the previous study. All treatm ents except the one m icrogram application of
gibberellin appeared to have hastened flowering slightly.
The elongation response of the petioles and peduncles was plotted
free-hand against the gibberellin concentrations (Figure 11). The response
of both plant p a rts diminished beyond the 500 m icrogram concentration. How­
ever, the intensity of the response between one and 500 m icro gram s was much
g re a te r for the peduncle. The rate of elongation for the petioles was less with
all concentrations of gibberellin applied, although the decrease in response to
the 1, 000 m icrogram application was less than for the peduncle.
Certain flowers that w ere not developing on gibberellin treated plants

TABLE IX
Effect of F o liar Applications of Gibberellin on the Vegetative and Floral
Development of Robinson Straw berry Plants. Plants Started in G reen­
house April 1 and T reated with Gibberellin April 9, 1958.

Observation

_
J-/O.LC
Date

0

M icrogram s Gibberellin p er Plant
- ----------------------------1
10
100
1,000
500

Petiole length (cm)

June 3

9.2

10.8

9.7

10.4

13.6

12. 9*

Peduncle length (cm)

June 5

8.7

11.8

15.3

18.8

24.8

22.9*

Pedicel length (cm)

June 5

3.0

3.1

3.7

3.8

4.5

5.1*

Flow ers p e r Plant

May 12

6. 4

7.6

7.8

7.7

8.6

8.1*

F ru it set (percent)**

June 3

47. 1

31.1

15.9

12. 9

0.0

0.0

Abnormal fruit (p er­
cent)

June 3

0.0

18.0 41.9

48.3

85.3

93.7

Crown elongation (cm) June 3

0.0

0.0

0.0

4.1

35.3

39.0

June 3

2.3

3.4

3.8

3. 3

2.6

2.8

1

0

10

1000

500

8.0

7. 5*

Runners p e r plant

Crown diam eter (mm) June 3

12.3

11.1

10.8

100
9.9

*Observations analyzed statistically. Values of various gibberellin tre a t­
m ents not underscored by a common line differ significantly at the 5 p e r ­
cent level.
**Fruit norm al in appearance possessing enlarged achenes and receptacular
tissue with no distortion in calyx region.

,o
o
o

- .o

o

... .

o

cs
CM

o
CN

00

o

00

sj9istupua3 ui qqSuaq

o

Figure 11. Petiole and peduncle response of Robinson strawberry plants treated with various concen­
trations of gibberellin. Values are averages of two experiments. Plants in first experiment started
February 12, treated February 14, and measured April 27, 1958. Plants in second experiment started
March 15, treated March 27, and measured May 16, 1958.
68.

w ere coated with either a one percent gibberellin-lanolin paste, or a one p e r­
cent indolebutyric acid-lanolin paste May 10 and 11, which was 12 to 13 days
a fte r flowering. The second and third flowers on the inflorescence to flower
w ere treated.

Forty percent of the flowers treated with the one percent

gibberellin-lanolin paste produced a slight swelling of the receptacle.

Eighty-

th ree percent of the indolebutyric acid-lanolin paste treated flowers produced
some enlargem ent of the receptacle.
The previous experiment was repeated a third tim e to more fully eval­
uate the effect of gibberellin on the rate of flowering and the effect of lanolin
paste applications of gibberellin or indolebutyric acid on fruit development of
plants previously treated with gibberellin. The response of Robinson straw ­
b e rry plants, started in the greenhouse April 9 and treated with 1, 10, 100,
500 o r 1, 000 m icrogram s of gibberellin on April 15, 1958 a re presented in
Table X. Results obtained were sim ilar to the previous experim ents with
two exceptions. No significant differences for petiole and pedicel lengths
w ere obtained between any treatm ents. All treatm ents appeared to have r e ­
sulted in slightly e a rlie r flowering.
The second and third flowers of the inflorescence to bloom on the
plants treated with 100, 500 and 1, 000 m icro gram s of gibberellin received an
application of either one percent gibberellin-lanolin paste o r one percent indole­
butyric acid-lanolin paste May 11. This was five to six days after the flowers

TABLE X
Effect of F o liar Applications of Gibberellin on the Vegetative and Floral
Development of Robinson Straw berry Plants. Plants Started in G reen­
house April 9,and T reated with Gibberellin April 15, 1958.

Observation

M icrogram s Gibberellin p er Plant
1
10
1,000
100
500

Date

0

Petiole length (cm)

June 4

8.5

8.4

8.5

9.4

10.1

10. 8*

Peduncle length (cm)

June 5

6.0

7.1

11.8

12.6

14.2

14. 4*

Pedicel length (cm)

June 5

2.2

2.2

2. 9

3.2

3.6

3. 3*

Flow ers p er plant

May 23

7.9

7.9

7.1

6.1

8.2

7. 4*

F ru it set (percent)

June 4

33. 4

71.4

19.3

16.3

0.0

0.0

Abnormal fruit (p er­
cent)

June 4

0.0

3.1

12.2

22.4

71.2

65.0

Crown elongation (cm) June 4

0.0

0.0

0.9

4.3

32.8

49.8

Crown diam eter (mm) June 4

10.8

10.1

9.6

8.5

6.8

6. 3*

June 4

0.9

1.6

1.1

1.5

1.0

1.4

Runners p e r plant

*Observations analyzed statistically. Values of various gibberellin
treatm ents not underscored by a common line differ significantly at the
5 percent level.

had bloomed.

Of the flowers treated with the gibberellin-lanolin paste, 88

percent produced a slight swelling of the receptacle. N inety-three percent
of the flowers coated with an indolebutyric acid-lanolin paste produced an
enlargem ent of the receptacle. Figure 12 shows that the indolebutyric acid
treated flowers attained a larger size than the gibberellin treated flowers.
F ru it size in both treatm ents was inferior to the size of norm ally developing
fruit.

The lanolin paste treatm ents did not resu lt in development of the

achenes.
The petioles, peduncle, flowers and crown exhibited the most consis­
tent responses to gibberellin investigations in the greenhouse. A chlorotic
effect was also observed in the young leaves. This condition tended to d is­
appear in the older leaves.

Figure 13 shows a developing leaf exhibiting a

light chlorotic m argin on each of the leaflets.
Plants of a seedling straw berry (M 1156), tran sfe rred to the green­
house in September and treated with 100 m icrogram s of gibberellin on October
24, 1957, did not exhibit the same morphological changes in the same pattern
as observed for the Robinson variety.

Figure 14 shows the elongation of the

main crown and then extension of a crown shoot from the elongated main
crown. Elongation of the branch crowns occurred on Robinson plants also,
but the elongation of all the crowns for this variety had a common origin and
did not elongate from an elongating crown.

Figure 12
Comparison of "fruit" from gibberellin treated plants coated
with one percent lanolin paste of indolebutyric acid or gibberellin, with
fruit from a non-treated plant which developed norm ally.
Left: F ru it developing from flower coated with one percent
indolebutyric acid-lanolin paste m ixture.
Center: F ruit developing from flower coated with one percent
gibberellin-lanolin paste m ixture.
Right: F ru it from non-treated plant.
Plants treated April 15 and flowers coated May 11, five to six
days after blooming. Photographed June 10, 1958.

Figure 13
Leaf of Robinson straw berry plant showing chlorotic
m argin of the leaflets developing following application of 100
m icrogram s of gibberellin. Plant treated December 16, 1957,
and photographed January 12, 1958.

Figure 14
Straw berry seedling (M-1156) exhibiting crown elongation
with extension of a crown shoot from the m ain crown which had
previously elongated.

73.

The crown of a M-1156 straw berry plant treated with 100 m icrogram s
of gibberellin elongated, but the length of the petioles arisin g from the elon­
gated crown did not differ from the non-treated plants (Figure 15). The peduncle
of another M-1156 plant elongated greatly with elongation occurring between
all the nodes of the p rim ary axis, but not between the second and third nodes
of the lateral branches of the p rim ary axis (Figure 15).
Rooted and non-rooted runner plants were used in 1957 to study
the translocation of the gibberellin stimulus in straw berry runners. Appli­
cation of 100 m icrogram s of gibberellin p er plant to either the m other plant,
f irs t runner or second runner plant resulted in longer leaf petioles and crown
elongation in the treated plant only. This vegetative stimulation was not ob­
served in the attached plants.

It did not appear to be translocated either from

the treated runner plant to the adjacent runner plants or the m other plant.
Sim ilar resu lts were obtained with both the rooted and non-rooted runner
plants.

Occasionally, runner plants developing from runners arising from

treated runner plants produced elongated crowns. Figure 16 shows plants
treated with gibberellin and the attached non-treated plants.
In addition to treating the three individual plants as in 1957, the
node between the firs t and second runner plants and the runner between the
f ir s t runner plant and this node were also treated in the 1958 investigation.
Applications of 500 m icrogram s of gibberellin p er plant w ere applied.

Both

Figure 15
Effect of gibberellin on the morphological development of stra w ­
b erry seedling (M-1156) plants in the greenhouse. Plants treated with
100 m icrogram s of gibberellin on October 24, 1957, and photographed on
January 12, 1958.
Top: N on-treated plant on left, and treated plant on the right.
Petioles on elongated crown of treated plant did not elongate in response
to gibberellin. Note elongated, weak, spindly peduncle and pedicels.
Bottom: Peduncle of treated plant showing elongation between
all the internodes of the p rim ary axis.

Figure 16
Comparison of Robinson straw berry plant and runner plants
which had gibberellin applied to either the firs t runner plant o r second
runner plant to determ ine if the gibberellin stim ulus moves through the
runner.
Top: Control, no gibberellin applied.
Center: Gibberellin applied to firs t runner plant only. Note
elongation of crown in treated runner plant only.
Bottom: Gibberellin applied to second runner plant only. Note
crown elongation has been lim ited to this plant.

rooted and non-rooted runner plants were evaluated for both Robinson and
Catskill v arieties.
Applications of gibberellin to the m other plant resulted in a vege­
tative response lim ited to the treated mother plant only for both varieties
with both rooted and non-rooted runner plants. Vegetative stimulation occurred
in the non-rooted firs t runner plant of both varieties only when the first run­
ner plant was treated.

The firs t runner plants that were rooted responded to

applications of gibberellin to the runner between the firs t runner plant and the
next distant node also.
Applications of gibberellin to the rooted second runner plants of the
Robinson variety was the only treatm ent to yield a vegetative response.

How­

ever, in the non-rooted Robinson runner plants and rooted Catskill runner
plants, vegetative stimulation in the second runner plant was obtained from
applications of gibberellin which had been applied to the second runner plants,
to the node between the firs t and second runner plants, and to the runner between
the firs t runner plant and next distant node.

The second runner plants, which

had not been rooted for Catskill variety, responded to applications of gibber­
ellin applied to the second runner plant and the runner between the firs t runner
plant and next distant node.
The response of different straw berry varieties to foliar applications
of gibberellin was investigated in 1957. Data presented in Table XI indicate

TABLE XI
Effect of F o liar Application of 100 ppm of Gibberellin on the Length in
Centim eters of Flower Stalks of Certain Straw berry V arieties
T reated April 29 and M easured May 26, 1957.
Petiole Length (cm)
Non-Treated Plants
T reated Plants

V ariety
Robinson

6. 2 - 1. 32*

13.1 + 2.8

P rem ier

5. 7 1 1. 8

1 1 .2 + 1.98

Catskill

12.2 1 2.26

24. 2 t 4. 35

Tennessee Beauty

14. 3 1 2. 07

24. 23 t 2. 87

8.8 t 2.18

17. 02 1 2. 30

M-1322

13. 2 t 2. 57

19 .7 1 2.64

Pocahontas

12. 5 1 2. 5

24.4 1 3. 67

Crimson Flame

14. 0 t 2. 73

24. 3 1 3. 9

Red Crop

/< v* - (L*}

*Standard deviation =~\ /

V

^ -------- - —

M-1

that all v arieties receiving an application of 100 ppm of gibberellin applied
A pril 29, 1957, produced significantly longer peduncles than the non-treated
plants.

The treated Robinson, P rem ier and Catskill plants yielded 92, 87

and 120 percent respectively as much fruit as the non-treated plants.

Fruit

from treated plants was norm al in appearance.
Plants set in the field in 1957 and treated with gibberellin exhibited
responses sim ilar to those obtained in the greenhouse. Peduncles elongated
and made inflorescences m ore accessible, which made blossom removal
during the first season easie r and faster. Data presented in Table XII show
the effect of applications of gibberellin on runner development. Observations
on June 29 indicated that plants receiving two or m ore foliar applications of
gibberellin had produced fewer runners than the control plants. This same
pattern tended to prevail on August 17 for P rem ier and Catskill varieties.
Except for plot I, which received four applications of gibberellin during the
sum m er, the differences between the plots in number of runners for the
Robinson variety on August 17 w ere small and inconsistent.
The effect of the applications of gibberellin on runner length and crown
elongation is indicated in Table XIII. Average runner length for all varieties
on June 30 was g rea ter in plot I, which had received three applications p rio r
to m easuring. M easurem ents for the other plots varied considerably i r r e s ­
pective of treatm ent.

Crown elongation was evident in all treated plots on

80 .

The Effect of Foliar Applications of Gibberellin on Number of Developing Runners of Prem ier, Catskill
and Robinson Strawberry Plants Planted in 1957 and Runners Counted June 29 and August 17, 1957.

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August 17, except plot III, which was not sprayed with gibberellin until July
7. The amount of elongation of the individual crowns tended to be directly
proportional to the number of applications of gibberellin applied.

Figure 17

shows a plant in plot I that received four applications of gibberellin. The
crown elongation resulted in a m ore distant location of the plant apex from
the p lan t's original root system.
One-half the plants in each variety in each plot were sprayed with a
100 ppm foliar application of gibberellin on May 4, 1958. The peduncle's and
petioles produced following this treatm ent w ere elongated and m ore erect
(Figure 18). Table XIV presents data on the fruit yield as affected by variety
and applications of gibberellin in 1957 and 1958. Yields in all plots were
reduced for plants sprayed with 100 ppm gibberellin on May 4, 1958. Many
plants sprayed with gibberellin in 1958 failed to produce fruit o r yielded ab­
norm al fruit sim ilar to abnormal fruits obtained in previous greenhouse
studies.
The yield in plots I and II w ere reduced by factors other than the ap­
plications of gibberellin. A heavy rainstorm in July, 1957 washed away plants
and covered others in plots I and II with eroded soil.

In addition, plants in

plot I had to compete with an infestation of quack g rass (Agropyron repens).
Plants in plot X w ere dug in the fall of 1957 and used for greenhouse studies
during the fall and w inter of 1957-58. In general, the yield of fruit in 1958

Figure 17
Straw berry plant receiving four foliar applications of 100 ppm
gibberellin between April 28 and July 7, 1957. Photographed August 18,
1957.

Elongation of main crown and two crown shoots has resulted in

a m ore distant location of the crown apices from the plant’s original
root system .

Figure 18
Three rows of straw berry plants on right sprayed with 100 ppm
gibberellin on May 4, 1958. Other rows not treated. Photographed May
31, 1958. Gibberellin resulted in elongated and m ore e re c t peduncles,
and flowers that w ere very prom inent.

83 .

84.

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did not appear to be increased in plots treated with gibberellin in 1957 com ­
p ared with the control plots. P rem ier and Catskill plots treated with gibberellin
in 1957 yielded slightly less fruit than control plots.

Differences between

the plot yields in the Robinson variety w ere inconsistent.
A severe late spring fro st on May 23, 1958, killed many of the p rim ary
flowers which w ere in bloom.

These flowers on plants sprayed with 100 ppm

gibberellin on May 4, 1958 exhibited an unusual pattern of development.
Figure 19 shows development in injured P rem ier blossom s compared to n o r­
m ally developing fruit. While the p istils had been killed by the freezing
tem peratures, the toral region above and adjacent to the calyx, expanded and
colored red; yet the receptacular tissue supporting the p istils did not swell.

Response of the Apple to Applications of Gibberellin
Shoot growth of rooted Mailing IX and XVI cuttings treated with 10, 50
and 100 m icrogram s of gibberellin in January and February, 1957 was com par­
able to shoot growth of the non-treated plants.

T here w ere no statistically

significant differences in shoot length on any of the dates that m easurem ents
w ere taken.
Rooted Mailing IX and XII cuttings sprayed with 100 ppm of gibberellin
at one week, two week and four week intervals, exhibited little response to any
of the treatm ents.

No statistically significant differences were obtained in

e ith er trunk diam eter or shoot elongation, from any of the treatm ents in either

Figure 19
Comparison of developing fruit from gibberellin treated plants
that w ere injured by spring frost with norm ally developing fruit from non­
treated plants.

Three fruits on left from plants sprayed with 100 ppm

gibberellin on May 4. Two fruits on right from control plants and not
injured by frost. Photographed June 10, 1958. F ru its from treated
plants, which had pistils killed by frost, show some receptacular develop­
ment beneath the p istil are a in the region of the stam ens.

of the Mailing IX or XII plants. A few of the Mailing XII plants died one to
two weeks after planting as a resu lt of poor root system s. Plants died i r r e s ­
pective of the treatm ents, but death occurred three to four days e a rlie r in
the gibberellin treated plants.
Foliar applications of 10 and 100 ppm gibberellin applied to bearing
apple tre e s in full bloom (May 9) appeared to have no effect on the fruit set
o r rate of fruit development in 1957. These phenomena were m ore influenced
by the amount of bloom on the branches used in this investigation than by any
application of gibberellin. Applications of gibberellin sprayed on the apple
tre e s three weeks after full bloom (May 28) had no effect on shoot growth or
fruit size.

Bearing apple tre e s, sprayed in 1957 with 100 ppm of gibberellin

eith er in full bloom o r three weeks later, flowered and set fruit norm ally in
1958.
Response of the C herry to Applications of Gibberellin
Shoot Growth:

Y ear-old Mahaleb cherry tre e s w ere started in the

greenhouse January 17, 1957, and treated with 10, 50 and 100 m icrogram s of
gibberellin p e r plant on F ebruary 2, 1957. An analysis of variance of the total
shoot elongation indicated that no significant differences existed between any
of the treatm ents on either April 6 o r 27, 1957. The length of the shoots de­
veloping from the term inal bud only of each tree to which the aqueous gibber­
ellin solution had been applied was m easured on April 6. A statistical analysis

Shese m easurem ents failed to indicate any significant differences between
any of the treatm ents.
Y ear-old cherry trees, treated with gibberellin following form ation
of term inal buds in the greenhouse in 1958, produced a second flush of growth
in the same season. The seasonal linear growth following applications of
gibberellin is illustrated in Figure 20, and presented in Table XV. There
w ere no differences in total linear shoot growth 13 days after the initial May
21 application of gibberellin.

During the following 20-day period, however,

each of the treated tre e s showed a visible increase in linear shoot growth of
both term inal and latera l buds. A tre e treated with 1, 000 ppm gibberellin
com pared with a non-treated tre e is shown in Figure 21. The lateral buds
induced to initiate shoot growth w ere in the distal region of the previous flush
of growth. All shoot elongation had ceased and term inal buds had again
form ed by July 3, 1958.
A slight flush of growth was obtained following the second application
of 500 and 1, 000 ppm of gibberellin on July 11, 1958. This growth was spindly,
weak and poor in vigor, and m ost of it wilted and died back by the time the
experim ent was term inated on August 20.
T runk diam eter was significantly g reater in all the gibberellin tre a t­
m ents (Table XV). L ateral branches on treated tre e s also exhibited an in­
c re ase in diam eter (Figure 21). There was an increase in fresh and dry

1000 p p m

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TABLE XV
Effect of Two F oliar Applications of Gibberellin on the Total Linear Growth,
Trunk Diam eter, F re sh and Dry Weights, and Top/Root Ratio of Mont­
m orency C herry T rees. T rees Potted in Greenhouse M arch 29,1958,
and T reated with Gibberellin May 21 and July 11, 1958.—
F oliar Application (ppm) GA p er T ree

M easurem ent
0

100

500

40.6

58.3

112.3

212.2*

.9

2.3

3.4

3. 5*

Original fresh weight

105.8

97.7

97.5

104. 7*

Final fresh weight

173.2

196.5

211.2

243. 8*

Final dry weight

64.8

70.8

77.7

89. 5*

Top dry weight

18.7

26.5

34.8

43.3*

Root dry weight

46.2

44.3

42.8

46. 2*

Total linear growth (cm)
Trunk diam eter increase (mm)

Top/root ratio

.40

.60

.81

1, 000

.94*

* Observations analyzed statistically. Values for various gibberellin
treatm ents not underscored by a common line differ significantly at
the 5 percent level.
—^All weights a re expressed in gram s.

91.

weights in all the gibberellin treatm ents.

T rees receiving foliar applications

of 1, 000 ppm gibberellin w ere significantly heavier than the controls and the
100 ppm gibberellin treatm ent.
The final dry weight of the roots was essentially the same (Table XV
and Figure 22). The dry weights of the tops increased with the increasing con­
centrations of gibberellin applied.

Top dry weight in both the 500 and 1, 000

ppm gibberellin treatm ents was significantly heavier than the control.

This

increase in dry weight of the tops in the gibberellin treatm ents with no in­
crease in the root dry weights resulted in an increase in the top to root ratio.
The flush of growth resulting from the 500 and 1, 000 ppm applications
of gibberellin on May 21 exhibited an unusual pattern of development. The
la tera l appendages appearing in the proxim al region of this flush of growth
appeared to be bud scales arising from elongated internodes and modified
stipules (Figure 23). These vegetative structures w ere light green and were
re stric te d to the lower region of the shoots which developed following the
initial applications of gibberellin.

Occasionally a sm all bud developed in

\

the axis of these modified appendages.
Effect on Flowering and Fruiting:

Foliar applications of 10 and 100

ppm gibberellin applied to Montmorency cherry tre e s in full bloom (May 2,
1957) had no effect on fruit set, fruit development, or shoot growth. Appli­
cations three weeks after full bloom (May 28, 1957) had no effect on fruit size
o r shoot growth.

93.

50

40

Dry Weight in G ram s

30

20

10

Root

Top
0

Control

100 ppm
5 00 ppm
Treatm ents

100 ppm

Figure 22. Effect of gibberellin on dry weight of tops and roots of
Montmorency cherry tre e s (applied May 21 and July 11).

Figure 23
Modified shoot development occurring on the second flush of
growth produced by year-old Montmorency ch erry tre e s following a
foliar application of 1, 000 ppm of gibberellin applied on May 21, 1958.
Note elongation of internodes between bud scales and m odification of the
stipules and leaves which developed at the nodes im m ediately above bud
scales.

Sim ilar effects w ere obtained on shoots developing from both

term inal and lateral buds. Photographed June 10, 1958.

94.

Differences in the pattern of flowering w ere observed in 1958 between
non-treated m ature bearing cherry tre e s and certain of the m ature bearing
c h erry tre e s treated with gibberellin in 1957. Flowering in 1958 appeared
norm al on all branches sprayed with gibberellin while in full bloom in 1957.
T rees sprayed with gibberellin three weeks after full bloom (May 28) in 1957,
p resented an altered flowering response in 1958 (Figure 24). T here was
some flowering in the distal portion of the shoots on the treated trees, but
none on any of the spurs.

T reated spurs were entirely vegetative, while

non-treated tre e s contained many fruiting spurs.

Flowering and fruiting

occurred only at the firs t few nodes adjacent to the term inal bud.

Response of the Peach to Applications of Gibberellin
Effect on Seedling Growth:

Shoot growth of seedling Elberta peach

tre e s treated with 10, 50 and 100 m icrogram s of gibberellin in February and
M arch, 1957, was comparable to the shoot growth of the non-treated seedling
tre e s . A statistical analysis indicated that significant differences in shoot
length did not exist between any of the treatm ents on any of the dates that
plant height was m easured.
Effect on Flowering and Fruiting:

Foliar applications of 10 and 100

ppm gibberellin applied during full bloom (May 2, 1957) to Halehaven peach
tre e s did not have any effect upon fruit set, and no observable effect upon
subsequent shoot growth and fruit development.

Figure 24
Effect of gibberellin on the flowering and fruiting of Montmorency
ch erry tre e s in 1958.
Top: T ree in foreground received a spray of 100 ppm on May 28,
1957. Only a few flowers w ere produced in 1958 on the tre e treated with
gibberellin in 1957, while the non-treated tre e s flowered profusely.
Photographed May 10, 1958.
Bottom: Shoots and spurs from above tre e and non-treated tree .
The two spurs and shoot on the left received 100 ppm gibberellin appli­
cation on May 28, 1957. N on-treated spurs and shoot a re on the right.
Photographed June 10, 1958.

96.

97.

F ru it size and rate of shoot development of Redhaven peach tre e s
was not affected when the tre e s were sprayed three and one-half weeks after
full bloom (May 28, 1957) with 100 ppm of gibberellin.

Foliar applications

of 1, 000 ppm of gibberellin two and one-half months after full bloom (July
20, 1957) did not affect the fruit size and rate of development of Halehaven
peaches. This application did resu lt in elongation of the shoot growth.
The post-bloom applications of gibberellin in 1957 resulted in
complete absence of flowers in the treated portion of the peach tre e s for
both v arieties in 1958 (Figure 25).

Shoots in the treated portion of the

tre e exhibited bare nodes throughout their central region. Sim ilar shoots
in the non-treated half of the tree flowered and produced fruit. Applications
of gibberellin during full bloom in 1957 did not affect flowering and fruit
set in 1958.

Figure 25
Effect of gibberellin on the flowering and fruiting of Halehaven
and Redhaven peach tre e s in 1958.
Top: Shoots exhibiting the flowering response of Halehaven peach
tre e s sprayed with 1, 000 ppm of gibberellin on July 20, 1957, and photo­
graphed May 8, 1958. T reated shoots (left) lack flowers.
Bottom: Shoots exhibiting the fruiting response of Redhaven peach
tre e s sprayed with 100 ppm gibberellin on May 28, 1957, and photographed
June 10, 1958. T reated shoots on left.

Note absence of fruit or vegeta­

tive growth in central portion of treated shoots.

99.

DISCUSSION

The generally observed effects of gibberellin on straw berry plants
a re in agreem ent with the only published reference to this plant (Wittwer and
Bukovac, 1958). These vegetative overgrowths - elongation of petioles,
peduncles, inflorescenes and crowns - paralleled those reported for many
herbaceous plants.
An increased petiole length was generally obtained on plants receiv ­
ing 10, 50, 100, 500 or 1, 000 m icro gram s of gibberellin. That an increased
petiole length was not obtained from any applications of gibberellin applied
April 15, 1958, may have been the result of using a gibberellin A^-A^ m ixture
instead of gibberellic acid, time of treatm ent, or length of elapsed time be­
tween treatm ent and tim e of m easuring.

It is doubtful, however, that the

lack of response resulted from using a gibberellin A^-A^ m ixture rath er than
gibberellic acid. Applications of the m ixture e a rlie r had resulted in signi­
ficant differences in petiole length, and a comparative study of the effect of
different gibberellin compounds on vegetative growth indicated little differ­
ence between gibberellin A1 and A (Bukovac and Wittwer, 1958).
Darrow (1934) observed that straw berry plants grown in the green­
house in w inter months, and placed under additional lighting, produced longer
petioles than plants grown under the natural day length. The lack of signifi­
cant differences between the means of the April 15, 1958 treatm ents may

m ay have been the resu lt of a longer photoperiod.

However, since all tre a t­

ment m eans w ere lower than the values for corresponding treatm ents in e a rlie r
investigations, it is probable that the m easurem ents of petiole length were
taken too soon - 19 days - after the application of gibberellin. The vegetative
response may have appeared accentuated if the m easurem ents of vegetative
growth had been delayed the same length of time as in e a rlie r studies.
The extensive crown elongation did not appear desirable.

Elongated

crowns lacked sufficient strength to rem ain erect and assum ed horizontal
positions as they continued to elongate. As the rosette-type growth was r e ­
established, the rosetted crown rooted when it came in contact with the soil.
Mann and Ball (1926) observed that plant vigor was often associated with the
degree of contact between the crown and the soil. Plants treated with 100 to
1, 000 m icrogram s of gibberellin often had decidedly less contact between the
crown and the soil than non-treated plants.
The slight inhibition of runners by applications of gibberellin appears
to be a different phenomena than that reported by Carlson and Moulton (1951)
and Carlson (1953). While they obtained runner inhibition with chemical tre a t­
m ents, the straw berry plants that they treated appeared normal at the end of
the season. Applications of gibberellin generally resulted in modification of
the pattern of the vegetative development.

The runner development appeared

to be inhibited, while the crown was elongating. As the crown begins to resum e

the ro sette-type of growth, the plants runner freely.

This could be the r e ­

sult of disappearance of the gibberellin stimulus.
An investigation of many straw berry varieties at Glendale, Maryland
by Waldo (1930) indicated that floral initiation begins in September or October,
depending upon the variety, and that the p rim ary flower was completely differ­
entiated and ready to bloom in late November. Plants dug in the field in
October and placed in the greenhouse immediately and treated with 100 m icro gram s of gibberellin p er plant on October 29, did not flower until the first
week in December.

Thus, while treated plants flowered e a rlie r than non­

treated plants, gibberellin did not appear to hasten floral differentiation.
These plants produced m ore flowers than the non-treated plants, however.
Since floral initiation in the straw berry occurs under short days, and the
flower bud is in a term inal position, it may be that applications of gibberellin
under such conditions enhanced floral differentiation.

If gibberellin promoted

bud activity and environmental conditions favored floral initiation, it is po s­
sible that the applications of gibberellin might promote continued differentiation
of floral prim ordia.
The failure of treated plants to produce normal fruit was probably
caused by lack of developing achenes.

Nitsch (1949) demonstrated a direct

relationship between receptacular development and the presence of viable
achenes.

Since em asculated flowers of non-treated plants produced norm al

fru it when pollinated with pollen from the gibberellin-treated plant, and pollen
from the treated plants appeared viable when stained with acetocarm ine, it
would seem logical that non-functioning pollen was not responsible for abnormal
fruit development in the plants treated with gibberellin.

It is likely that the

applications of gibberellin had an adverse effect on the sexual reproductive
p ro cess of the straw berry plant during megasporogenesis, megagametogenesis,
or embryological development. Since plants sprayed with 100 ppm of gibberellin*
when in full bloom, produced normal fruit, it is doubtful if the embryological de­
velopment was affected.
Rappaport (1957) observed that tomatoes treated with gibberellin yielded
parthenocarpic fruit, and Wittwer et aL (1957) found gibberellin to be m ore
effective than indoleacetic acid in induction of parthenocarpy in tomatoes.
Nitsch (1952) states that "fruits developing parthenocarpically in nature are not
seedless at the tim e the ovary development is definitely set in motion". However,
the parthenocarpic fruit produced lacks embryos or endosperm s. This would
seem to indicate that tomatoes developing parthenocarpically on plants treated
with gibberellin might have formed a megagamete.

Since neither the achenes nor

the receptacle of some flowers developed on the straw berry plants treated with
gibberellin, it is probable that such flowers did not form megagametes. This
would not indicate, however, whether m egasporogenesis or megagametogenesis
was affected by the application of gibberellin.

103.

Flow ers produced by gibberellin-treated plants, which were coated with
either one percent gibberellin-lanolin or one percent indolebutyric acid-lanolin
paste, did not produce as large a receptacle as the norm ally developing fruit
on non-treated plants. When Nitsch (1950) removed achenes from developing
fru it nine days after fertilization, and coated the "berry" with a one percent
indolebutyric acid-lanolin paste, the "b erries" attained a size comparable to
norm ally developing fruit.

"Berries" in his investigation had the advantage of

developing under the influence of developing achenes during the first nine days,
however. This could partially explain how he obtained larg e r receptacles in
his investigation than were obtained in these studies from sim ilarly treated
flowers on the gibberellin-treated plants. G ardner and Marth (1937) and
Hunter (1941), working with p istillate varieties, obtained parthenocarpic fruit
by applying applications of indoleacetic acid, indolebutyric acid and naphthylacetic acid to the flowers of straw berry plants which had not been pollinated.
While these plants had no source of pollen, it is probable that the flowers had
form ed a megagamete. The enlargem ent of the receptacles occurred, however,
without any developing embryos.
Lack of receptacular swelling in the are a of p istil attachment was not
the only abnorm ality of the fruit development.

No explanation is offered as

to why the basal a re a of the receptacle would swell slightly, two to three weeks
a fte r the flowers bloomed, and take on a red color at the same time that com ­
parable norm ally developing fruit ripened.

The effect of the gibberellin stimulus apparently was not translocated
from the m other plant to any of the runner plants in the transport investigations
a s evaluated by vegetative stimulation. Nor was the stimulus observed to
trav el from any of the treated runner plants to another non-treated runner
plant o r the attached m other plant.

The stimulus was observed to move from

one node on a runner to the next distant node where a runner plant was de­
veloping.

When the gibberellin was applied directly to the stolon between a

runner plant and a node, the stimulus was observed to travel in both directions
to runner plants. Hartm an (1947) observed that the flowering stimulus would
trav el from a m other plant growing under a day length which was photo-induc­
tive for flowering, to a runner plant growing under long day conditions and
resu lt in flowering in both plants.

Runners that did not develop from treated

straw berry plants until after the gibberellin had been applied, appeared to have
som etim es translocated the stimulus as evidenced by the production of runner
plants with elongated crowns. Apparently the gibberellin stimulus did not
travel in a basipetal direction in the crown and, therefore, would not be tra n s ­
located through runners which had developed p rio r to the application of the
gibberellin.
M icroscopic investigations by Goff (1899-1900) indicated that floral
initiation occurred e a rlie r in the growing season for the apple than for the
peach and cherry, and that differentiation of floral p a rts occurred e a rlie r in

the ch erry than it did in the peach.

It would be logical to assum e that floral

induction m ust precede floral differentiation and that the length of the induction
period might vary among plant species.
Sensitivity to external stimuli during floral induction probably varies
among plant species also.

Results from investigations of summer sprays of

potassium a-naphthaleneacetate to reta rd "bud-break" of fruit tree s the follow­
ing spring indicated that the apple was m ore resistan t to the effects of such
applications than the cherry and peach (Hitchcock and Zimmerman, 1943).
The peach was m ost sensitive.
Defloration and defoliation experim ents by Struckmeyer and Roberts
(1942) indicated that induction occurred at least three weeks p rio r to the ap­
pearance of blossom prim ordia for the Wealthy apple.

If floral differentiation

in the apple v arieties investigated occurred in June, it would appear from r e ­
sults obtained, that the applications of gibberellin had little or no effect on
floral induction in the apple.

If induction occurred p rio r to the applications

of gibberellin, then the applications did not appear to destroy the induction
effect.
Went (1957) reported that young, non-bearing peach tre e s would not ini­
tiate floral prim ordia until after a period of exposure to tem peratures of 4 to
10 degrees C for two to three months. The cold period m ust be followed by a
warm period for floral initiation, and then by another cold period to break the

dorm ant bud and enable it to flower.

If this were true for mature bearing

tre e s also, then the applications of gibberellin after bloom must have counter­
acted any induction effect of the preceding winter. Why did not the application
during the period of full bloom inhibit flowering the following spring? This
would seem to indicate that either induction m ust occur after the blooming
period, or that the flowering stimulus was not as subjected to destruction by
external factors at this tim e.

Since floral differentiation in the peach v a rie ­

ties studied probably was initiated in August and September, it would appear
that, for the peach, induction occurs after the period of full bloom in the p re ­
vious season, and that the applications of gibberellin completely counteracted
the induction stim ulus. The peach may also be m ore sensitive to gibberellin.
That the cherry trees, receiving a post-bloom application of gibberellin
produced some blossom s in the term inal region of the previous season’s shoots,
would seem to indicate that the gibberellin effect on floral initiation tended to
dissipate or that blossom buds were differentiated over a longer period of time.
It might also indicate that the sensitivity of the cherry tree to gibberellin is in­
term ediate to that of the apple and peach in regards to floral initiation.
The mechanism whereby gibberellin overcam e the dormant condition
of the buds on the initial flush of growth of the year-old Montmorency cherry
tre e s is difficult to interpret. Perhaps the cause of "rest" in the buds was
photoperiodically induced.

The effect of photoperiod on dormancy in the sour

cherry, Primus cerasus L ., is not known. Long days result in continuous
growth in the peach, Prunus p ersica (L .) B atsch., yet long days do not p re ­
vent the onset of dormancy in the cherry, Cerasus avium L. (Nitsch, 1957b).
It would appear that the young sour cherry tre e s studied in these investi­
gations m ust fall in the latter group, since the tre e s formed term inal buds
in May under the naturally occurring day lengths.

It is probable that the

phenomena responsible for the second flush of growth in the young Montmorency
c h erry tre e s following the initial applications of gibberellin are sim ilar to
the cause for growth of photoperiodically-induced dormant plants treated with
gibberellin.
Exposure of plants to cold is the usual means of overcoming dormancy.
G ibberellin has been able to fulfill this chilling requirem ent in the peach
(Donoho and Walker, 1957). The review by Samish (1954) also indicates that
the products of anaerobiosis a re the active agents in breaking dormancy.
Thornton (1945) subjected freshly harvested potato tubers to atm ospheres
containing only two to ten percent oxygen and broke both dormancy and apical
dominance in the treated tubers.
The m aterial used for the initial applications of gibberellin was an
em ulsifiable concentrate containing 0. 5 percent potassium gibberellate.

The

oily base of this m aterial may have resulted in an anaerobic condition in the
dormant buds and thus overcome the dormant condition. The gibberellin then

108.

could be acting as a stim ulus to a non-dormant bud.

The source of gibberellin

in the second application, however, was a technical grade powder and contained
no oily base. Yet a slight flush of growth was produced following the second
gibberellin spray, which would tend to refute the value of the oily base of the
original application. This weak, spindly growth following the second applica­
tion, may have been the result, however, of only a partial breaking of the dor­
mant buds.
It is possible that gibberellin may exert its influence on dormancy,
genetically. Phinney (1956) overcam e the inhibiting effect of a dwarfing gene
in single-gene dwarf maize plants with gibberellin applications. If dormancy
w ere genetically controlled, gibberellin might overcome the effect of the in­
hibiting gene or genes.
It is m ore probable that the response of the dormant buds to gibberellin
involves a relationship with the auxin content of the plant. Application of auxin
alone has been found to be insufficient to break " re s t” of cambial cells (Samish,
1954).

Nitsch (1957a) found that sumac plants treated with gibberellin contained

a level of endogeneous auxin higher than non-treated plants.

He also observed

that short days resulted in a reduction in the level of endogeneous auxin and
an increase in the level of endogeneous inhibitors.
The theory of auxin activity proposed by Muir and Hansch (1951) m ain­
tains that reaction of auxin with the plant substrate occurs at the ortho position

on the unsaturated ring of the auxin. Perhaps plants produce compounds which
re a c t at the ortho position of the auxin ring o r make reaction between the auxin
and substrate at this position impossible, thus resulting in inhibition or the
form ation of inhibitory compounds. Application of gibberellin then might block
such an auxin inactivation process by reacting with the compounds produced
in the plant before such compounds could inactivate the auxin. The application
of gibberellin might exert its effect by reacting with the inactivated auxin com­
plex to liberate the auxin. E ither method of action would result in a higher
auxin content in the plant, and might aid in breaking dormancy.
Explanation of the modification of stipule and leaf development in the
basal portion of the second flush of growth produced by year-old Montmorency
ch erry tre e s treated with gibberellin is difficult, since no anatomical studies
w ere made of representative buds.

It is probable that the embryonic stru c ­

tu res w ere very sensitive to the chemical and therefore the developmental
p attern was altered.

The second flush of growth probably resum ed a normal

growth habit, as the gibberellin effect diminished. With Liriodendron tulip ifere L ., the leaves for the firs t eight nodes of the shoot are formed in the
developing bud during July to October of the previous season, and the other
six to 12 leaves a re formed the current year during the period of shoot expan­
sion (Millington and Gunckel, 1950). If a sim ilar pattern of development existed
for the sour cherry, then the modified appendages of the second flush of growth

110.

might correspond to the nodes developing in the bud at the time of treatm ent.
The norm al pattern of development would be observed where prim ordia devel­
oped afte r shoot elongation was initiated.
The third flush of growth produced following the second application
of gibberellin to the young Montmorency cherry trees, was of poor vigor, and
m ost of these weak shoots wilted and died back.

F oster (1932) observed in

Oklahoma that in the Black Hickory (Carya Buckleyi, var. Arkansana) organ
form ation ceased after the middle of May, and further development in the new
term inal buds consisted in enlargem ent and specialization. Perhaps, since
a second flush of growth was produced following the initial application of
gibberellin, the subsequent buds were not so complete and fully developed
as buds on the original shoots.

It would appear that there is a lim it to the

amount of linear growth that a young Montmorency cherry tree can produce
in one year in response to applications of gibberellin, or that the concentra­
tion of gibberellin in the second application may have been toxic to the new
growth.

Term inal buds form ed on the second flush of growth were sm aller

and it is likely that the embryonic shoots were very sensitive to the gibber­
ellin sprays.
Since a second flush of growth was produced by cherry tre e s sprayed
with gibberellin, resulting in an increased number of leaves and increased
foliage area, m ore photosynthetic products should have been produced.

This could account for the increased dry weight of the treated tree s. The
tre e s treated with gibberellin not only produced m ore growth, but were stocky
and appeared very desirable com m ercially.

This in contrast to the spindly

growth reported for many herbaceous plants treated with gibberellin.
That the year-old Mahaleb seedling tree s grown in the greenhouse
and treated with gibberellin did not produce an increase in shoot growth
was probably the resu lt of timing of the application. While M arth et_aL (1956)
obtained the greatest amount of shoot elongation in treated plants when gib­
berellin was applied just as the stem s began elongation, data from this in­
vestigation indicate that cherry tree s are m ore responsive when treated
after the term inal bud has set.

112.

SUMMARY

An investigation was conducted during 1957 and 1958 to determine
the response of the straw berry, apple, cherry and peach to applications of
gibberellin.
Robinson straw berry plants grown both in the greenhouse and field
plantings w ere treated with gibberellin. The plant responses to the appli­
cations of 10 to 1, 000 m icrogram s p e r plant, or 100 ppm sprays of gibber­
ellin w ere generally characterized by m arked increases in elongation of the
petioles, peduncles, pedicels and crowns. Crown diam eter was decreased
with the resulting crown elongation. Runner formation appeared to be in­
hibited during the period of crown elongation. None of the applications of
gibberellin increased fruit size or yield either in the greenhouse or field
studies.
Applications of gibberellin p rio r to blooming resulted in failure of
some of the straw berry fruit to develop normally. Treatm ents of 100 to 1, 000
m icrogram s of gibberellin resulted in the largest number of abnormal fruit.
F ru it lacked developing achenes and the receptacular tissue in the area of
the p istils failed to enlarge.

Some flowers on treated plants produced a slight

swelling of the to ral tissue acropetal to the calyx and basipetal to the area
of the p istils.

One percent lanolin paste applications of either indolebutyric acid or
gibberellin applied to the p istils and the associated area of non-developing
flowers on plants treated with gibberellin produced a slight swelling of the r e ­
ceptacle in the p istil area. The longer this application was delayed after bloom,
the less the amount of swelling occurred. Receptacular development was
g rea ter on indolebutyric acid-treated fruit than for the fruit coated with a
gibberellin-lanolin paste, especially when the application was delayed 12 to 13
days after blooming had occurred.

Both treatm ents produced fruit of inferior

size.
Robinson straw berry plants grown in the greenhouse and treated in
November and December with 100 m icrogram s of gibberellin produced m ore
t

flow ers than control plants.

L ater gibberellin treatm ents (March and April),

however, did not appear to resu lt in increased flower number.
The gibberellin stimulus did not appear to move in a basipetal direction
in the crowns. When 500 m icrogram s of gibberellin were applied to the stolon,
the stim ulus apparently moved laterally, in both directions, in the runner, but
appeared to be m ore readily translocated distally.
Rooted East Mailing IX, XII and XVI cuttings, grown in the greenhouse
and treated either with 100 m icrogram s per plant or 100 ppm sprays of gibber­
ellin, did not exhibit any increase in shoot length or diam eter.

Branches of

m ature bearing apple tre e s sprayed with either 10 or 100 ppm of gibberellin

during full bloom (May 9, 1957), or 100 ppm three weeks later (May 28, 1957),
produced a crop sim ilar to non-treated tre e s with no increase in fruit size.
T reated tre e s flowered and fruited norm ally the following year.
F ru it yield of Montmorency cherry trees, sprayed with either 10 and
100 ppm gibberellin while in full bloom (May 2, 1957), or with 100 ppm 26 days
la te r (May 28, 1957), did not appear to be affected in either fruit size or num­
ber.

Flowering in the tre e s treated in full bloom was normal the following

year, while the application 26 days after full bloom partially inhibited flowering
the following spring.

Some flowering occurred in the distal portion of the p re ­

vious y e ar’s shoots only on treated tree s.
O ne-year-old Mahaleb seedling cherry trees, grown in the greenhouse
and treated with 100 m icrogram s gibberellin just as shoot elongation began,
did not produce increased shoot growth.

One-year-old Montmorency cherry

trees, grown in the greenhouse and treated with 100, 500 or 1, 000 ppm gibber­
ellin a fter the tre e s had form ed term inal buds, produced a second flush of
growth. T reated tre e s produced m ore linear growth, and when harvested 90
days after the initial treatm ent, had a g reater dry weight. Root growth was
not increased o r decreased by these treatm ents.
Stipule development was modified in the basal region of the second
flush of growth produced in the same season by tre e s receiving foliar appli­
cations of 500 and 1, 000 ppm gibberellin. This was accompanied by a sup-

p ressio n of leaf development. There appeared to be elongation of the in te r­
nodes between some bud scales also. A second application of gibberellin 61
days after the initial treatm ent resulted in a slight flush of growth which was
undesirable in appearance and died back.
Seedling E lberta peach tree s treated with 100 m icrogram s of gibber­
ellin during shoot elongation did not develop m ore rapidly or over a more
extended period of tim e than the control trees.

Mature bearing Halehaven

peach tre e s, sprayed with 10 and 100 ppm gibberellin in full bloom (May 2,
1957), o r with 1, 000 ppm gibberellin two and one-half months later (July 20,
1957), did not vary from non-treated tre e s in fruit number, size, and time
of ripening. T rees treated in full bloom flowered normally the following year,
but tre e s treated two and one-half months later produced no flowers the fol­
lowing spring. Mature bearing Redhaven peach tree s sprayed with 100 ppm
gibberellin 20 days after full bloom (May 28, 1957) exhibited no response to
gibberellin during the season treated, but failed to flower the succeeding
year.

Many nodes on the treated tre e s which failed to flower the following

season, w ere also lacking in vegetative growth.

116.

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