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EXPERIMENT STATION LIBRARY

station IJuUetiii 274

Jimc, 1933

POLLINATION AND FRUIT
SETTING IN THE APPLE

By L. P. LATIMER

Cheesecloth cages used to keep insects from trees
during pollination experiments

New Hampshire Aaricultiiral Experiment Station

University of New Hampshire

Dui'ham, X. H.

TABLE OF CONTENTS

PAGE

Development of Orcharding and the Pollination Problem ... 3

Flower Bud Formation and Development 5

Mechanics of Apple Fertilization

Pollination 8

The Flower 8

Fertilization of the Egg Cells 10

Pollination of the Apple Under New Hampshire Conditions

The Need for Pollenizers 13

Effect of Location 15

Tests for Self-unfruitful Orchards 16

Pollination Experiments in New Hampshire, 1927-32

Pollination of Mcintosh 17

Pollination of Cortland 25

Pollination of Delicious and Gravenstein 25

Relation of Pollen Viability to Set of Fruit in Cross Pollination . . 26

Effect of Position of the Flower in the Cluster on Set of Fruit . . 26

Pollination and Orchard Planting and Management

Coincidence of Blooming Periods of Varieties 27

Bees in the Orchard 30

Distribution of Pollenizers in the Orchard 30

Reworking Orchards to Pollenizers Zl

Temporary Relief from Lack of Pollenizers 38

Summary 38

Pollination and Fruit Setting

in the Apple

By L. p. LATIMER

Pollination has come to be a general problem in our New England
orchards in recent years due to the fact that fewer varieties of apples are
now planted in a given orchard than was the case a quarter of a century or
more ago.

I. Development of Orcharding and the
Pollination Problem

The earliest settlers in America brought apple seeds from Europe and
planted them here. As time went on more seedlings were developed and
occasionally plants of a named variety were imported from Europe. Later
the special merits of certain seedlings were appreciated and grafts made
from them to perpetuate the type. Thus different settlers and their descend-
ants in the new world developed fruit gardens containing several to many
trees of quite different types.

In those days wild bees, including bumble bees, were also plentiful and
well able to carry all the pollen needed for pollination of self-sterile varie-
ties which, then as today, would not set fruit when pollenized with their
own pollen.

The result was that in those early times the large mixture of varieties and
plentifulness of wild bees in proportion to the size of planting led to no
difficulties of set as are experienced today. Hence no problem of pollination
became apparent.

Up to the middle of the 18th century, commercial orchards as we now
know them had not been definitely established in America. Grafted trees
were planted before this time, but plantings of "common" or "cider" apples
still predominated.

The rapid growth of New York City, and its importance as a seaport,
resulted in a large market and outlet for American apples. Boston was a
similar center. During the last quarter of the 18th century, considerable
trans-Atlantic shipments of apples were made.

The Newton Pippins (green and yellow) had l)y this time come to be
known as America's highest-quality apple. Its popularity on the continent
followed the receipt of a box by Benjamin Franklin in London in 1758. The
increasing tendency since then has been to plant only those varieties which
seemed most profitable in large centers of population and in foreign trade.
This resulted in the development of the truly commercial orchard where
only grafted and budded varieties of proven merit were planted.

At first the list of such varieties was rather large, because of the various
tastes and demands of consumers who were still used to the products of the

4 N. H. Agricultural Experiment Station [Bulletin 274

older fruit gardens. As the years passed, fewer and fewer varieties were
planted. Local demands and the profit from the different varieties in the
market governed the planter's choice. Varieties tender to cold or unpro-
ductive of large and regular crops, were culled from the orchard. Those
especially subject to disease and insect attacks and those not universally
popular because of color, flavor, or keeping qualities, came to be placed in
the catalog of obsolete varieties.

New varieties were eagerly sought in order to obtain apples better in
some respect than those already established. These changes finally led to
conditions occasionally found in the last of the 19th century and often dur-
ing the present century, where apple plantings that bloomed heavily failed
to produce fruit.

One of the earliest examples of this condition appeared in the pear
industry. Many plantings of Bartlett pears in large blocks were made in
the 70's and 80's. When they reached bearing age they produced little or
no fruit. The trouble was traced to the fact that under most conditions the
Bartlett is partially or wholly self-sterile. The remedy was to plant some
other variety with the Bartlett to provide pollen for its flowers, thus insur-
ing a crop of fruit.

This discovery was made and published by M. B. Waite (1) in 1892-3
and the knowledge has since been invaluable to fruit growers. Even now
self-unfruitful varieties are occasionally planted in solid blocks. In New
England the Mcintosh falls in this class. History will without doubt repeat
itself in this respect whenever new varieties are introduced that are more
profitable than existing ones.

When the error of planting a self-unfruitful variety in a solid block is
discovered perhaps 10 or 15 years later, the remedy is to graft pollenizers
into certain trees in the orchard and to include pollenizers in future plant-
ings. The mistake is costly because five or six years pass before the pollen-
izers grafted into the orchard bloom sufficiently to be effective in cross
pollination. This would make the tree needing pollination at least twenty
years old before a full crop could be produced.

Not so well known is the fact that good pollenizers themselves may not
be readily pollenized by the main crop variety which has shown need of
pollination. Although Delicious wall pollenize Mcintosh, for example, this
is no indication that Mcintosh will in turn pollenize Delicious. Further-
more, inter-sterility may exist between two varieties.

Several varieties of apples in New England produce paying crops, even
when i)lanted in large blocks without pollenizers. They may therefore be
considered self-fruitful sorts. Baldwin is outstanding in this class.

The fact that a variety may be self-fruitful does not signify that it is also
a good pollenizer. The self-fruitful Baldwin is practically useless as a pol-
lenizer for any other important commercial variety grown in New
Hampshire.

Darwin emphasized in 1859 that "Nature . . . abhors perpetual self-
fertilization." He indicated in his work that cross- fertilization is of value
in the plant kingdom. Half a century earlier investigators were aware that
bees carried pollen from one flower to another but were unaware of the
exact nature of the benefit.

(1) M. a. Waite. The pollination of pear flowers. U.S.D.A. Bur. Veg. and Plant Path.
Bui. 5 (1893)

June. 1933] Pollination and Fruit Setting in the Apple 5

The need of cross-pollination is thus a relatively new discovery following
in the footsteps of commercialization of the apple industry. Since the time
Waite attempted to discover what effects the self and cross-transfer of pol-
len would have on the resulting fruit, it has heen determined that the
amount of fruit setting on the various varieties can be increased through
cross-pollination by many other sorts and that, in most cases, this is a very
necessary consideration.

To determine the list of suitable pollenizers for the various cultivated
sorts, certain experiment stations have conducted pollination tests. The re-
quirements of some of the older sorts have been pretty well worked out, but
there will always be the necessity for determining the requirements of new
varieties as they are developed, and likewise the efTectivenss of new varie-
ties as pollenizers for the older ones.

The experiment station may save growers much time by recommending
quality orchard varieties that will poUenize one another satisfactorily. With
a list of such varieties and some idea of the degree of coincidence in their
blooming dates, the grower should be able to pick desirable combinations.
It is to be assumed that he will exercise some judgment in choosing varie-
ties with relation to market demands, climatic and regional adaption and
other points related to profitableness.

II. Flower Bud Formation and Development

Inasmuch as the set of fruit is intimately connected with the blossom
(the apple fruit being formed from the basal portion of the flower), it is
very essential to keep the tree in such a state of vigor that it will produce a
plentiful supply of strong flower buds.

The first essential is that the tree be grown properly. A strong frame-
work, proper fertilization of the soil and good management of water-
supply are necessary. When the tree has reached the age to produce flower
buds, attention must be paid to this process. Without these, or with the
formation of only weak ones, no fruit will result.

The flower-cluster buds on the apple tree are produced principally on
short growths or shoots called spurs. With some varieties flower-bud clus-
ters are also formed at the tips of new shoots or in the axils of the leaves
of new growth. In any event this is a summer development preceding
blossoming.

Microscopic examination of buds on spurs of the Baldwin and Mcintosh
has shown that in New Hampshire the first stages of flower-bud differenti-
ation can be detected from the middle to the last of July.* At this time
with the aid of the microscope, buds that are going to form only leafy
shoots or spurs may be readily told from those that have the possibility of
ultimately forming fruits. It must be remembered that for the buds to ma-
ture into good blossoms and fruit, favorable conditions must be maintained
for their continued development.

* E. J. Rasmussen. The period of blo-ssom-bud differentiation in the Baldwin and Mcintosh
apples. Amer. Soc. Hort. Rci. Report 26-255-260 (1929).

N. H. Agricultural Experiment Station [Bulletin 274

Fig. 1. Bud of Baldwin. July 29, 1928 (after Rasmussen).
Typical of leaf and shoot buds.

n^F^'

/

■.*:;

Fig. 2. An earlv stage in tlie development of a flower bud cluster.
Ikddw'.n, August 20. 1928 (after Rasmussen).

June, 1933] Pollination and Fruit Setting in the Apple 7

Fig. 1 shows just how a leaf or shoot bud looks when cross-sectioned and
observed under the microscope. The hard outer scales enclose embryonic
hairs, leaves and leaf primordia. The growing tip located in the center has
a smooth, rounded surface. All leaf and flower buds in the first stage of
development show this appearance.

After the first of July in New Hampshire, some of the buds on trees of
bearing age may show a change in the character of this central growing
point. Instead of remaining nicely rounded, the outline of the growing tip
becomes marked by angular projections. These elongate, so that after a
period of some three weeks, the buds have changed in appearance to that
noted in Fig. 2. Here the rudiments of the various flowers of the cluster
have been formed. Fig. 3 explains the parts and their regular succession.
The first prominences to appear are those of the outermost part or calyx ;
those of the pistil and ovules are last.

Under favorable conditions the flower buds continue to develop slowly

Fig. 3. Illustrating the development of the flower bud cluster. Bald-
win, March 9, 1933 (25x). A. Terminal bud of the cluster. B. Lateral
buds of the cluster, a. Primordia of calyx or sepals, b. Primordia of
petals, c. Primordia of stamens, d. Primordia of pistil, e. Cavity
which eventuallj' becomes the ovary with its contents — ovules, etc.

through fall and winter. During April the primordia rapidly complete their
development into calyx, petals, stamens and ovary. Then in May warm
weather brings rapid growth and swelling of the flower buds. They subse-
quently burst into bloom, with matin-e pollen and ovules.

Much can happen to prevent many or all of these embryonic flower buds
from reaching the mature stage. Factors that strongly inhibit fruit or
flower-bud formation are: 1. A heavy set' of fruit such as may occur espe-
cially in biennial bearers like Baldwin, Wagener, and Wealthy. 2. Heavy
shading, as from foliage of an extra-vigorous tree. 3. Cool w^eather or

8 N. H. Agricultural Experiment Station [Bulletin 274

dark days about the time fruit-bud formation usually takes place. 4. Im-
proper balance between food and nutrients, which may be caused by lack of
leaf surface due to insect attacks or lack of minerals in the soil, especially
nitrogen. Once flower buds have been initiated, conditions for carbohy-
drate, moisture, and mineral supplies must be kept as near the optimum as
possible to insure continued development of the buds.

The tree must also be brought safely into the rest period by prevention
of growth late in the season. Late growth may result from injudicious
applications of nitrogen or excess moisture in the soil. In the cultivated
orchard a cover crop planted about July 1 will alleviate the latter condition.

In the winter there is danger with the more tender varieties that 25° to
30° F., below zero will freeze some or all of the flower buds. Once killed by
freezing, no other flower buds will form in time to open in the spring. The
leaf buds are more hardy and do not freeze at these temperatures. Provided
the hazards of winter have been avoided, there is still danger from spring
frost where a temperature of 25° or 26° F. may totally ruin the fruit crop
through freezing of the unfolding buds or open blossoms. Under such con-
ditions the pistils are usually injured. The pollen may also be injured and
often the ovules.

To insure the proper nutrient and moisture conditions, an appHcation of
nitrogen is generally made in the sod or sod-mulch orchard a short time
before the trees come into bloom in May and a mulch applied a little before
July 1 to conserve moisture. This early nitrogen application is beneficial
to the setting of fruit, to fruit-bud formation, and to the further develop-
ment of the fruit. Light frost after the buds have appeared may not inter-
fere at times with the set or pollen formation but may cause injury to the
outer layer or epidermis of the flower parts. The result will be a russeted
fruit or one with russet rings, cracks, or malformations.

III. Mechanics of Apple Fertilization

Pollination:

Pollination means the transfer of pollen from the stamens to the pistils
of the flowers. With apples this is mostly eft'ected by insects, principally the
various kinds of bees. The pollination of apples cannot be assured through
the agency of the wind.

Pollination is only one step toward insuring a set of fruit. FertiHzation
of the egg cells in the ovules is necessary with most apples to cause fruit to
set. This fertilization process results in the formation of seed. Further
growth of the tissue of the fruit is directly correlated with seed develop-
ment. The pollen of only certain varieties can under certain conditions
effect satisfactory fertilization and set, hence the need to study the value of
difl"erent varieties as pollenizers for the different apple sorts.

To show the relation of various factors to the fertilization of flowers and
set of fruit, a short description of the structure of the flower and the pro-
cess of egg fertilization is presented.

The Flower:

Fig. 4 shows the cross section of an apple flower. Figs. 5, 6 and 7 show
and describe the essential parts in detail. The important parts of the flower
with relation to pollination are the stamens and pistils. Each stamen con-

June, 1933] Pollination and Fruit Setting in the Apple

Fig. 4. Cross section of apple flower, a. Sepal or calyx, b. Petal,
c. Filament of stamen, d. Anther of stamen, containing pollen, e. Pis-
til, f. Stigma of pistil, g. Ovary containing ovules. It is the ovary and
the adjacent fleshy parts of the flower that ultimately become the fruit.

• /

Fig. 5. Upper portion of stamen (Mcintosh), a. Anther (40x).

b. Filament.

10 N. H. Agricultural Experiment Station [Bulletin 274

sists of an anther, a small yellowish sac attached to the end of a slender
\vhite filament or stalk. The anthers contain thousands of minute rounded
cells known as pollen grains which contain sperms, the male elements of the
flower.

The cultivated varieties of apples ordinarily have 20 stamens, although
occasionally small petal-like organs may be found to have replaced some of
the stamens, and sometimes the filaments of the stamens may appear petal-
like.

Each pistil in the apple consists of five slender green stalks which are
coalesced in the lower part to form a single cylinder of tissue, usually more
or less covered with fine hairs. The five individual parts of the pistil are
called styles. Each style is capped with a stigma. The stigma has a papil-
lated surface (see Fig. 7.). It is on this surface that the pollen grains are
left by the insects and this is the place where the germination of the pollen
grains takes place.

The female portion of the flower consists of three parts : ovary, style
and stigma. The ovary is the basal portion of this apparatus. It lies im-

Fig. 6. Cross section of mature anther of Mcintosh (35x). a. Fila-
ment attachment, b. Cavity containing pollen grains, c. Integuments
which open out as the anthers dry, exposing the pollen.

bedded in the tissues beneath the calyz and contains the ovules, occasionally
20 in number ])ut in most varieties 10. Each ovule contains a female element
or egg cell, so that with perfect fertilization it is possible in some varieties
to develop 20 seeds in the apple. Fertilization and complete development
of all the ovules into seeds seldom occurs in any apple, five to 10 seeds
being the usual number.

Fertilization of the Egg Cells:

To fertilize the 20 ovules of a Mcintosh apple ovary, at least 20 dififer-
ent pollen grains are needed. As it happens only a few of the thousands of
pollen grains ])roduce(l ultimately reach an ovule to effect fertilization.

Individual pollen grains when mature are crowded closely together in
the anther. When the flower bud opens and the anther is exposed to the
sun and dry air, it splits open leaving the pollen exposed.

This pollen looks to the unaided eye like a fine, powdery-yellow dust.
Each grain is too small to be seen as an individual by the unaided eye. The
pollen grain (Fig. 8A) when saturated with water is slightl}- triangular in

June, 1933] Pollination and Fruit Setting in the Apple

11

uJ-^^J^O^X

A

FiQ. 8

B

-a

— a

Fiq.9

Fig. 7. End of pistil of Mcintosh (45x). a. Papilla-like terminal cells
of stigma, b. Pollen grain caught in terminal cells.

Fig. 8. A. Pollen grains after absorbing water (270x). B. Pollen
grains before absorbing water (270x).

Fig. 9. Pollen grains after three hours in germinating medium of 15
per cent sucrose (270x). a. Pollen tubes shortly after germination of
the pollen.

shape but with a well-rounded surface which is somewhat roughened, enab-
ling it to adhere to the bodies of bees and other insects that visit the flowers.
Perhaps 75,000 pollen grains are produced by each vigorous, healthy
apple flower and all these could easily be carried on the body of a single
bee. Should each pollen grain from a single flower ultimately fertilize an
ovule, then the pollen from this one flower would be capable of causing the
setting of from 7,500 to 15,000 fruits, or the crop of 10 trees. What actu-
ally happens is that not more than one pollen grain in 10.000 ever reaches

12

N. H. Agricultural Experiment Station [Bulletin 274

and fertilizes an ovule ; so it takes the blossoms on one whole tree of a
pollenizer to insure the production of a good crop on ten other trees.

Under natural conditions in the orchard many factors prevent the effi-
cient utilization of pollen. Weather and the presence or lack of insects are
most important in this respect. The honey and bumble bees are the principal
insects involved in the transfer of apple pollen.

The mature pollen grain is a specialized cell containing a great amount of
stored food. A large nucleus occupies a portion of it, or in the case of apple
pollen, two nuclei, one of which is known as the "tube" nucleus because it
directs the course of the pollen tube growth dow-n the style into the ovary.
The other is known as the generative nucleus because it contains the male
elements that function later in the fertilization process.

Fig. 10. Terminal and undcTlying cells of stigma (OOOx).

The nuclei and the stored food are enclosed by two layers of material.
The outer one is composed chiefly of cutin, a substance very resistant to
moisture and to the penetration of chemical substances.

The bee visiting the opened flower in search of either nectar or pollen
brushes against the opened anthers and becomes covered with pollen grains
whicli stick to the hairs covering the body of the insect. Some of these
grains mav be deposited on the surface of the stigma of other flowers or
possibly the same flower.

On reaching the stigma the normal pollen grain germinates by sending
out a so-called "tube" (Fig. 9.). This penetrates the tissue of the stigma
and grows downward through the central portion of the style in the direc-
tion of the ovary. This i)rogress is accompanied by the movement of the
tube nucleus down through the stylar tissue, with the generative nucleus
traveling liehind or l)eside it. During this period the latter divides into two
sperm nuclei.

June, 1933] Pollination and Fruit Setting in the Apple

13

As the nuclei move farther and farther down the style, the older part of
the tube becomes plugged with callose, which separates the growing part
forever from the original pollen grain.

The pollen tube finally reaches the ovary, enters an ovule and discharges
the male nuclei or sperms. One of these fuses with the egg nucleus and
an embryo is formed. The ovule then develops into a structure known as
the seed. Without fertilization the seed would not develop. If reports of
their occurrence can be considered authentic, cases of seed development
without fertilization of the ovules rarely occur in the apple.

It is the development of viable seed that is so important to the set and
further development of the fruit. A tree soon sheds flowers in which a
sufficient number of ovules are not fertilized. Other flowers in which ovules
become aborted are also generally dropped. Flowers may set fruit heavily,
apparently with plenty of seeds, yet the June drop may be heavy because of
the competition for food and water. To insure the sticking of fruit that has
been fertilized, it is important, therefore, that the tree be properly supplied
with moisture and nitrogen.

__b

Fig. 11. a. Pollen grain after alighting on stigmatic surface b.

IV. Pollination of the Apple Under
Neyv Hampshire Conditions

The Need fcr Po'Jenizers:

Self-unfruitfulness. A large majority of apple varieties and nearly all
of the important commercial sorts are unable to develop seed or set a crop
of fruit when pollenized with their own pollen. These are considered self-
unfruitful, because of the general inability of the pollen to efifect self-
fertilization.

In orchard observations the self-unfruitfulness of certain varieties has
often been strongly suspected, but carefully controlled hand-pollination
experiments have been necessary to prove the fact. The supposition has
also been advanced that certain varieties were especially good poUenizers
for these self-unfruitful sorts. This has often been indicated in orchards,
one section of which has a given variety in the vicinity of certain other

14 N. H. Agricultural Experiment Station [Bulletin 274

varieties. Heavier sets of fruit have consistently been obtained in such
areas as compared with other parts remote from these pollenizer trees.
This can be checked through hand-pollination experiments.

Even though liberally supplied with bees, plantings of large blocks of a
single variety of apple such as Delicious, for instance, have often failed to
set fruit. This has frequently led to the supposition that under existing
environmental conditions the lack of set was due to self-unfruitfulness.
This would later be confirmed when good sets of fruit were obtained after
the introduction of other varieties to act as pollenizers. Emphasis should be
placed on the fact that one must be sure lack of bees is not the cause of
poor pollination before concluding that the trouble is lack of good pol-
lenizers.

From general observations and from carefully controlled experiments,
it has been possible to classify most of the commercial varieties of apples
into a number of classes ranging from the self-fruitful — those setting fruit
with own pollen — to the kinds which are entirely self-unfruitful. A good
many varieties will set a small amount of fruit through self-pollination, but
this will not be enough to produce a paying crop.

Given varieties in different sections of the country differ as to the degree
of self-unfruitfulness. Generally the soil and cHmatic conditions are widely
different in places where such wide differences in self-fruitfulness and un-
fruitfulness exist. A good example is the Mcintosh which is partially self-
unfruitful in the humid eastern half of North America, yet is reported as
being self-fruitful in Montana and Washington, the arid northwestern sec-
tion of the United States. Baldwin, on the other hand, is considered self-
fruitful in northern New England, but has been reported as being self-
unfruitful in some other sections.

Among the varieties that are self-unfruitful to a great enough degree to
reduce the set below any desirable commercial quantity in New Hampshire,
may be listed Mcintosh, Delicious, Gravenstein, Rhode Island Greening,
Northern Spy, Wagener, Fameuse, Golden Delicious. Winesap, Stayman
Winesap and Winter Banana. Certainly many other varieties also fall into
this class, but it is not within the scope of this bulletin to include them.
Some are new and have not as yet been thoroughly tested at this or nearby
stations. Others are now obsolete or of little or no commercial importance.

Cross-unfniitfulness. Cross and inter-unfruitfulness may also occur
among certain varieties. This fact is of importance to the apple grower
because plantings are often made of varieties which may pollinate in one
direction but not in the other. Gravenstein will not satisfactorily pollinate
Mcintosh, for example, but Mcintosh is an excellent pollenizer for Grav-
enstein. Again. Northern Spy and Rhode Island Greening in some sections
seem among themselves to be unfruitWl, neither being able to set a crop of
fruit when one pollenizes the other. ^^S'^r^^ J 'y"^'->''-i< '>-■--(■''] ^

Inter-fntitfuhicss. Fortunately a few varieties are mter-f ruitful ; that
is, cross-jiollination is successful in both directions. This minimizes the
nvunber of varieties to be planted in a given orchard and may be an advan-
tage under many conditions. Cortland and Mcintosh are good examples.
They will satisfactorily pollenize one another. Gravenstein and Delicious,
Gravenstein and Wagener, and Mcintosh and Oldenburg are similar inter-
fruitful combinations.

June, 1933 J Pollination and Fruit Setting in the Apple

6?

Self-fniitf Illness. Self- fruit fulness occurs where fruit setting is satis-
factory from the application of a given variety of pollen to a flower of the
same variety. The presence of bees helps to increase the set in such
varieties by increasing the transfer of pollen. Many large blocks in New-
Hampshire consist entirely of Baldwin and always set heavy crops. Hand-
pollination tests confirm these observations. The set on self-fruitful sorts
may generally be further increased through cross-pollination, but in some
cases this may not be desirable. Too heavy a set may be detrimental.

H the fruit of pollenizers does not have a high market value, self-fruitful
sorts are economical.

Effect of Location:

The effect of locality on pollination and fruit setting has already been
mentioned. Variations in the results of certain varieties as pollenizers for
others, or in the self-fruitfulness of certain varieties, can be noted only
when wide areas are considered. Mcintosh is self-unfruitful to a high
degree throughout New England, for example, but self-fruitful to a much
greater degree in Washington (1) and Montana (2). Baldwin which seems
self-fruitful in New Hampshire to the satisfaction of commercial growers
has been found by Hewlett (3) to be doubtfully so in Ohio.

Differences in the self-fruitfulness of these varieties, on the other hand,
does not vary appreciably within a distance of several hundred miles, as
indicated by a comparison of New Hampshire experiences with experi-
ments in Massachusetts (4) and New York (5). The same is indicated in
the case of Mcintosh self-fruitfulness when comparing the results of Mon-
tana (2) and Washington (1). Nevertheless, Mcintosh and other varieties
nearly always set heavier crops in some sections of New England than in
others.

Mcintosh orchards located on hillsides and hilltops in some areas of New
Hampshire are noted for their heavy set of fruit, which is generally better
than in valley orchards. Even when pollenizers are reduced to a minimum
at the higher elevations, the set of fruit is sometimes superior to that at
lower elevations where better provision has been made for pollination.

Observations of Mcintosh planted in blocks have sometimes led the
grower to believe that in these orchards the Mcintosh was self-fruitful.
Generally in such cases, however, a few odd varieties may be discovered
in adjacent fields w^hich would easily be a source of pollen. Frequently a
grower will overlook this fact, the usual feeling being that only common
cultivated sorts can pollinate cultivated varieties. This assumption is wrong
in most cases, for it is more often the fact that such odd varieties or seed-
lings make exceptionally good pollenizers.

A location at a small elevation may often be more favorable for fruit
setting, because of the greater freedom from frost at blossom and fruit-

(1) O. M. Morris. .Studies in upple pollination. Wash. Agr. Exp. Sta. Bull. 1(53. (1921)

(2) F. M. Harrington and W. E. Pollinger. Pollination of the Mcintosh apple. Mont. Agr.

Exp. Sta. Bull. 2.56. (1932)

(3) F. &'. Howlett. Apple pollination studies in Ohio. Ohio Agr. Exp. Sta. Bull. 404. (1927)

(4) F. C. Sears. The pollination problem in Massachusetts apple orchards. Rpt. Mass. Fruit

Growers Assn. (1928)

(5) L. H. MacDaniels and A. J. Heinicke. Pollination and other factors affecting the set of

fruit with special reference to the apple. Cornell Agr. Exp. Sta. Bull. 497 (1929)

16 N. H. Agricultural Experiment Station [Bulletin 274

Fig. 12. Cross section of ovary (20x). Note locule or cavity in which
the ovule is located, a. Base of pistil.

setting time. The flower parts become progressively more susceptible to
low-temperature injury as they approach the stage when the ovule becomes
fertilized. The advantage of an elevation is well known with regard to
lessening damage from spring frosts.

Location as affected by climate causes variations in the time that various
varieties come into bloom. Varieties that coincide in time of bloom in one
place may bloom on different dates elsewhere. This same variation may also
occur in the same location in different seasons.

Tests for Self -unfruitful Orchards:

It is easy to test whether or not a lack of fruitfulness which has persisted
year after year in an orchard is due to lack of pollenizers. If some blossoms
of the variety are hand pollinated with pollen of a known good poUenizer
and a liigh percentage of set occurs while the usual unfruitfulness of the
remainder of the blossoms persists, then it may be concluded that either
bees or pollenizers are lacking. If bees had also been provided in the
orchard without increasing the set, then the conclusion would be justifiable
that pollenizers were absent.

Another method to test whether the cause of unfruitfulness is lack of
pollenizers, would be to introduce some branches of a good known poUen-
izer into the orchard at blossom time. If plenty of bees are also present
and a set of fruit is obtained, this is proof of the lack of pollenizers.

For such reasons as these the recommendation is always made to inter-
plant varieties in the apple orchard to insure a good set of fruit.

June, 1933] Pollination and Fruit Setting in the Apple 17

V. Pollination Experiments in
New Hampshire, 1927-1932

Pollination of Mcintosh:

In 1927 work was begun to determine the effectiveness of various com-
mercial varieties as pollenizers for Mcintosh. In addition to hand pollina-
tions in screened cages, observations were made to compare the open set on
Mcintosh trees adjacent or near to various other varieties and on those
somewhat isolated from other varieties.

In 1930, reciprocal pollinations were made with Delicious, Gravenstein,
and Cortland.

In 1927 a moderately vigorous 20-year-old Mcintosh tree was enclosed in
a wire-screen cage just before the flower buds began to open. This tree was
located in a sod orchard and had been fertilized with five pounds of sodium
nitrate or ammonium sulfate annually since coming into bearing.

In 1929 a different Mcintosh tree of corresponding size and vigor was
similarly caged in the same sod orchard.

In 1930 in another orchard which is grown under cultivation with com-
bined intercrops and cover crops, tw^o Mcintosh trees were enclosed just
before the first blossom buds opened. The cages consisted of wooden
frames covered with cheese cloth. These trees were 11 years old (from the
time of planting), had borne two crops, and were of ordinary good vigor.

In 1931 two other trees were tested in the same cultivated orchard.
These were also enclosed in cheese-cloth cages.

To increase the amount of data and to compare effects in differently
located sections, a Mcintosh tree was caged in cheese cloth in a southern
New Hampshire orchard where normally trees of a given variety come into
bloom from four to seven days earlier than at Durham. Two young Cort-
land trees w-ere also caged and crosses made.

Because of the desire to try out some of the new Mclntosh-like sorts,
one of the leading questions of growers in New Hampshire is the efficiency
of newer varieties as pollenizers. It was therefore concluded that some value
to growers might be derived from using a few of the newly originated
varieties as pollenizers for Mcintosh. The work was therefore discontinued
of testing as pollenizers varieties which had shown themselves to be consist-
ently good pollenizers, or had proven less desirable from a standpoint of
commercial value.

Pollen was obtained from the new varieties by removing the anthers
from buds gathered as late as possible before the petals began to unfold
and before danger of the stamens becoming contaminated by insect visits
to the flowers. Since fresh pollen was gathered daily and none was held
for use another day, the danger of loss of vitality in the pollen was reduced
to a minimum.

Pollen was placed on the stigmas of opened flowers when the maximum
number on a cluster were apparently in a receptive condition. In this way
an average of four blossoms per cluster were pollinated. Unopened buds on
a cluster, flowers that were apparently near the end of the receptive stage,
and imperfect flowers w^ere removed at this time of pollination.

18

N. H. Agricultural Experiment Station [Bulletin 274

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June, 1933] Pollination and Fruit Sktting in thk Apple 19

In 1927, 1929 and 1930 all flowers in an individual cluster were pollinated
with the same variety of pollen hut various spurs on the same branch were
often pollenized with different varieties.

Pollen was applied in 1931 and 1932 only to lateral flowers in the cluster,
all terminals being removed. Another feature which dift'ered from previous
experiments, and which it was thought would give more uniform results,
was the pollination of four flowers in every cluster used. This procedure
was adopted on the basis of results presented in previous publications by
the author (1, 2). The reasons for choosing these methods in ]ireference
to the spur-unit plan are also discussed in these papers.

Screen cages were kept over the trees throughout the season. But when
cheese cloth was used, it was removed from the frames as soon as it was
certain that the last flower to open was past the receptive stage. All condi-
tions were therefore maintained as near to those of an open orchard as
possible in 1930, 1931 and 1932.

Counts of set were made both before and after the June drop. The June
drop was light during 1931, perhaps due to an unusually large amount of
rainy weather during the early growing period.

A second or late drop, unusual in New Hampshire, occurred in August —
about a month after the June drop. This feature is discussed in another
paper (2).

At the time of bloom in 1927 weather conditions were cool and for the
most part rainy. In 1928 pollination experiments were not carried on ex-
tensively because of almost continuous daily downpours of rain. In 1929
the first period of bloom was accompanied by mild days and cold nights,
followed by an unusually cold, cloudy, misty period succeeded by pleasant
weather. In 1930 the weather was unusually warm and dry throughout the
blossom period and was by far the most favorable for bee flight.

Weather conditions were unsually favorable for fruit setting in 1931.
Bright sunshine and high temperature prevailed w'ith little rain during the
period of full bloom. The least favorable feature was the rapidity with
which the trees came into full bloom and the shortness of the period when
stigmas w-ere receptive.

Fine weather prevailed at pollination time in 1932.

Table I shows the results of five seasons' tests on Mcintosh pollination
in New Hampshire with relation to the per cent of blossoming spurs setting
fruit after hand pollination.

The data show that for all practical purposes, Mcintosh may be consid-
ered self-unfruitful. When Mcintosh pollen is brushed onto the stigmas
(hand pollination) a slightly higher set of fruit is to be expected with this
variety than where the flowers are left undisturbed except by wind or rain
(check).

Many previous workers suggest that when 30 per cent of the blossoming
spurs develop fruit to maturity on full-bearing Mcintosh trees, this is rep-
resentative of a satisfactory crop from a commercial point of view. If these
individuals are correct, then Mcintosh is deciflcdly in need of pollenizers.
In the five years of experiment, the highest set was 11.8 per cent. A set of

(1) L P. Latimer. Pollination studies with the Mcintosh apple in \cw Hampshire. Proc.

Amer. Soc. Hort. Sci. (27) 1930.

(2) L. P. Latimer. Further observations on factors afifecting fruit setting of the Mcintosh apple

in New Hampshire. Proc. Amer. Soc. Hort. Sci. (28) 1931.

20

N. H. Agricultural Experiment Station [Bulletin 274

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June, 19v^3J Pollination and Fruit Setting in the Apple 21

fruit on two to three per cent of the blossoming spurs after self-polhnation
is usuahy the case with Mcintosh.

That varieties differ among themselves in the ability to poUenize Mcin-
tosh is also indicated. Baldwm seems to be the least satisfactory, but this
is to be expected for the results of numerous investigators show that Bald-
win is an unsatisfactory poUenizer tor many other varieties. Where Bald-
win pollen was used on Mcintosh the highest and lowest set is seen to be
18.6 and 4.5 per cent, respectively, of the spurs that blossomed. This is
far below the standard for a commercial crop of Mcintosh.

Gravenstein and Red Gravenstein are also quite unsatisfactory as pollen-
izers for Mcintosh. In only one year out of five was the set of spurs above
30 per cent where these pollen varieties were used. Two to 10 per cent was
the usual set of blossom spurs. Although slightly better on the average
than Baldwin, Gravenstein is far from being dependable in producing a
commercial crop of Mcintosh.

Delicious seems to be the variety most constant in ability to cause a set
of fruit on Mcintosh. During the five years' experiments the percentage of
blossom spurs setting fruit on Mcintosh has been more constant when
Delicious pollen was used than with any of the other good pollenizers. This
is true whether the trees were grown m sod or under cultivation.

The percentage of blossom spurs setting fruit on Mcintosh varied from
63 to 7S per cent when this pollenizer was used. This is a remarkably small
variation. A few other varieties may have caused a larger set when used as
pollenizers but this is not necessarily an advantage. It might necessitate
heavy subsequent thinning and even then be somewhat detrimental to the
normal annual-bearing habits of the Mcintosh.

Melba likewise seems to be a reliable pollenizer. The low results obtained
on the Tuttle farm in 1931 were due to a somewhat weak growing condi-
tion in the tree used in the experiment, as indicated by the results of all
other pollenizers used with that tree.

Cortland, Milton and Wagener may also be considered very satisfactory
pollenizers.

Although tested fewer years Fameuse, Lobo, Medina, Oldenburg, Red
Astrachan, and Wealthy also seem promising as pollenizers for Mcintosh.
The actual set of fruit on Mcintosh when these varieties are used as pollen-
izers has not dift'ered greatly from the results obtained with Delicious
pollen.

One problem connected with the development of good commercial apples
is the shape or form of the fruit. This becomes important when one consid-
ers the difficulties in packing lopsided fruit and its lower market valvie.
That lopsidedness of Mcintosh fruits in New Hampshire is due largely to
lack of satisfactory pollination is seen from a comparison of Tables I, II,
and III. The varieties that are notably poor pollenizers for Mcintosh,
namely Mcintosh, Baldwin and Gravenstein, cause a greater development
of lopsided Mcintosh fruits than when the more satisfactory pollenizers
are used.

It is apparent that this is connected with poor pollenizing ability \vhen
one views Table III. One also sees that with these pollenizers Mcintosh
develops an unusually small number of seeds. These have been found to
exhibit poorer germinating power than seeds from Mcintosh poUenized by
the better pollenizers.

22

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June, 1933J Pollination and Fruit Setting in the Apple 25

Another method of indicating the efficiency of certain varieties of pollen
in causing fruit to set on Mcintosh is evident from Table I\' which records
the average numl)er of fruits per cluster. The data show that rarely more
than one fruit develops on a Mcintosh cluster pollinated by Baldwin, Grav-
enstein, Mcintosh or Red Gravenstein. It has been shown previously
(Table I) that these varieties are also incapable of causing a good set of
fruit on the tree as a whole where Mcintosh is cross pollinated.

Fameuse heads the list from the viewpoint of the number of fruits per
cluster. Usually about two per cluster were obtained where Mcintosh was
pollinated by this variety (Table IV). It has already been noted that
Fameuse is one of the leaders in causing a high percentage of fruit spurs
of Mcintosh to develop fruit as a result of cross-pollination. Wagener is a
close rival in this respect.

Pollination of Cortland:

The methods used in Cortland pollination experiments w^ere similar to
those followed with Mcintosh. Cheese-cloth cages only were used to ex-
clude insects.

Cortland as indicated in Table V seems at times to be partially self-fruit-
ful, especially when hand or bee pollinated. In both cases the set was
heavier than when the flowers were left entirely to the efTects of the wind
and rain.

Baldwin was found to be a poorer pollenizer for Cortland than Cortland
itself. A fair set of fruit was obtained when Delicious pollen was used but
was not as satisfactory as that effected by several other varieties. The high-
est set of Cortland fruit was generally obtained when Mcintosh or Wag-
ener was used as pollenizer. Gravenstein produced a satisfactory set of
fruit in two of the three years, and Red Gravenstein in 1932. The data
show that in 1932, however, the set with Gravenstein and Red Gravenstein
as pollenizers, was no improvement over that obtained with Cortland pollen
itself. Lobo pollen does not seem to give a satisfactory set of fruit on Cort-
land. The most important finding is that Cortland and Mcintosh are cp&ss-
fruitful varieties. ' ^^^""^

Pollination of Delicious and Gravenstein:

One year's results (1930) indicate that Delicious and Gravenstein are
nearly self-unfruitful. In neither case was fruitfulness increased by the
use of Baldwin pollen. Although the use of Gravenstein, Wealthy and
Wagener resulted in a set of fruit on 32.6 per cent, 30 per cent and 26.8
per cent, respectively, of the blossoming spurs on Delicious, this might be
considered unsatisfactory from a commercial viewpoint, as the tree used in
the experiment, although vigorous, was decidedly alternate in its bearing
habit. Mcintosh and Winter Banana as well as Red Astrachan might also
be considered in most seasons as unavailable for Delicious pollenizers be-
cause of the earliness of their blooming season as compared with Delicious.
(See Table V.)

One year's results with Gravenstein indicate that Delicious would be a
satisfactory pollenizer, except that its late blooming habit fenders it uncer-
tain. The periods of bloom of Delicious and Gravenstein do not overlap
enough of the time to make availability of pollen dependable under field
conditions. (See Table V.)

26 N. H. Agricultural Experiment Station [Bulletin 274

Next to Baldwin, Cortland and Oldenburg failed to show themselves as
satisfactory pollenizers for Gravenstein. Mcintosh, Red Astrachan, Wag-
ener and Early Harvest did not produce a high set in 1930, yet owing to the
heavy blooming habit of Gravenstein, 30 per cent would ordinarily be
sufficient.

The foregoing results of pollination with Mcintosh, Cortland, Delicious
and Gravenstein emphasize the fact that these varieties are not only self-
unfruitful but may fail to be poUenized satisfactorily by some other varie-
ties. Self -unfruitful varieties used as pollenizers may not bear fruit unless
these facts are taken into consideration.

Relation of Pollen Viability to Set of Fruit in Cross Pollination:

Poor set when certain varieties are used as pollenizers is probably due to
a large extent to natural abnormality of the pollen of these varieties. These
abnormalities may vary in different seasons.

Many investigators have found in artificial germination tests that Bald-
win pollen germinates very poorly. Many of the pollen grains are imperfect
in their development. Gravenstein also usually exhibits rather poor germi-
nating power, but in this respect is less constant throughout a period of
years than Baldwin. These facts partially explain why the low sets of fruit
indicated in Table I are obtained when these varieties are used as pollen-
izers for Mcintosh. It is also known that these varieties dift'er from
Mcintosh in the genetical make-up of the tissues.

Delicious is just the opposite. It produces well- formed pollen grains
which germinate from 95 to 100 per cent on artificial media. It is one of
the most satisfactory all-round pollenizers in existence.

Effect of Position of the Flower in the Cluster on Set of Fruit:

That all of the flowers in the cluster do not open at the same time is well
known. The first to open is the central or terminal flower in the cluster.
The latest to open are those at the base of the cluster.

Generally the first flowers to be pollinated in the cluster will remain on
the tree through the June drop. Under most Xew Hampshire conditions,
this will be the terminal flower. Yet if weather conditions are unsatisfac-
tory for bee flight and consequently for pollination when the terminal
flowers are receptive, the latter may fall oft" during or before the June drop.
Those blossoming later, if they open under more favorable weather condi-
tions, will then produce the fruit. With some varieties the first flowers to
open may be injured by frost occasionally because of their advanced devel-
opment, and again the later opening buds will be the ones to develop fruit.

\\'hcthcr the crop came mainly from terminal or from lateral flowers of
the cluster can easily be determined with Mcintosh. Fruits developing from
lateral flowers are flatter in shape and have usually much longer and more
slender stems than those from terminal flowers of the spur. Fruits from
terminal flowers are usually decidedly more attractive in appearance, and
have better form and size due partly to the greater seed development. The
position of these flowers in the cluster predetermines shape and other differ-
ences. Even in the dormant winter buds the superior size of the terminal
flower and its larger stem diameter may be seen. They are in a better posi-
tion to receive food, minerals and water from the tree.

June, 1933] Pollination and Fruit Setting in the Apple 27

To test the differences in anatomy of terminal and lateral flowers and the
effect of these on the resultant fruit crop, a number of trees have been used
experimentally. Terminal flowers were tagged and the two types of fruit
developed were observed at harvest time. In a future publication a compari-
son of the rate of growth in terminal and lateral flowers of the cluster will
be presented.

Table VI shows data obtained in preliminary experiments to determine
quantitatively difference between terminal and lateral fruits on the cluster.
The trees concerned had all terminal flowers tagged while they were open.
At harvest time the tags still remained on the stems of the terminal fruits
which could easily be separated out and compared with the lateral ones on
the same tree. In all cases the terminal flowers produced larger fruits. In
addition to this important feature terminally developed fruits have better
form as indicated by the greater percentage of lopsided fruits among the
laterals. Aside from the better position of the terminal fruits to receive
foods and water from the tree, two explanations of this better form and
size are possible from a glance at the data. An increase of approximately
20 percent in weight is accompanied by an increase of two seeds per fruit
in the terminals over the laterals. The shorter and thicker stems of the
terminal fruits may also aid in causing a better development of the fruits.

In these trees terminal and lateral fruits were rarely matured on the
same clusters, so that difference in size and shape could be considered as
due purely to anatomical and physiological differences between the terminal
and lateral flowers. That there is less difference in diameter than in length
between fruits from terminal and lateral flowers can be determined from
Table VI. It may be seen that the ratio between length of terminals and
laterals is greater than between the diameters of the two.

VI. Pollination and Orchard Planting
and Management

For satisfactory pollination, it is evident, first of all, that the apple must
be pollinated by the apple, the pear by the pear, etc. This does not mean .
that fruits of different genera and in many cases of different species cannot
possibly be crossed, but such crosses are rare and usually only result, when
they are possible, after hand pollination.

Coincidence of Blooming Periods of Varieties:

It would be unreasonable to interplant an orchard of one variety with
trees of another variety and expect cross pollination to occur if the two
varieties did not have at least a few flowers open at the same time. This is
evident because we know that the pollen is shed and is available to insects
only after the flowers have fully opened.

Even though the flowers of an early blooming sort may in some years
remain on the tree until the opening of some of the flowers of a later vari-
ety for which pollination is desired, in other years, especially when unusu-
ally warm weather prevails at blossom time, the flowers of the early variety
may be shed before the later one opens its buds. The pistils are in a recep-
tive condition as soon as or even just before the buds open. The bumble-
bee is the only insect able to push the petals of unopened buds apart, and it
would only be such insects that could possibly pollinate unopened flowers.

28

N. H. Agricultural Experiment Station [Bulletin 274

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June, 1933J Pollination and Frtit Setting in the Apple 29

Because of the scarcity of bunibleliecs, tliis unusual procedure is not
dependable.

A late-blooming sort would not be apt to cause any more successful set
on an early blooming sort because the pistils soon begin to disintegrate after
full bloom. Even if the pistils have not begun to shrivel, unless flowers
are ])romptly pollinated, the ovules may begin to disintegrate before the
pollen tubes can reach them. As has already been mentioned, locality may
alter to a certain extent the relation of blooming dates among certain
varieties.

V^arieties may be separated into five general classes with relation to date
of bloom : very early, early, mid-season, late and very late. Some may have
a short and others an extended period of bloom, depending on the positions
of blossom clusters on the tree. Most varieties of apples produce the major-
ity of their flowers only on spurs arising from wood more than one year
old. A few' varieties produce most of their flowers terminally on slender
shoots. Some also produce fruit from lateral buds on last season's new
shoots. Others yield "flowers in clusters of all three types.

With trees producing all types the period of bloom covers the longest
possible period. When only one type is produced, the period of bloom is
exceedingly short.

With relation to position of clusters, Mcintosh, Gravenstein, Red
Astrachan, Melba, Milton, Fameuse, Delicious, Baldwin, Northern Spy,
Red Gravenstein and Starking fall in the class of trees coming into full
bloom nearly all at once, since their flowers are rarely produced on anything
but spurs on older wood.

Cortland flowers appear both on spurs and terminally, while Wagener,
Wealthy, and Winter Banana possess all three types of clusters with rela-
tion to position on the tree, with spurs predominating.

Where more than one type of cluster is present, the order of bloom is,
spurs first and usually lateral clusters last. Partly because of this fact Cort-
land, Wagener and Wealthy are regularly available as pollenizers, except
that Wagener and Wealthy tend to a large extent to bear only in alternate
years.

As classified under the headings, very early to very late, the blooming
period of apples in New Hampshire is as follows :

Very Early — Red Astrachan, Gravenstein, Red Gravenstein.

Early — Fameuse, Gravenstein, Red Astrachan, Mcintosh, Melba, Milton,
Oldenburg, Wagener, Early Harvest.

Mid-Season — Delicious, Oldenburg,, Cortland, Wagener, Wealthy, Me-
dina, Lobo, Winter Banana, Orleans, Starking, Williams, Baldwin.

Late — Golden Delicious, Cortland, Macoun, Wealthy, Wagener, North-
ern Spy, Winter Banana.

Very Late — Northern Spy, Macoun, Northwestern Greening, Rome,
Wealthy, Winter Banana.

Even in a given class some varieties are slightly earlier than others, and
those in one class may overlap into another somewhat. Very young trees
may bloom slightly later than mature trees of the same variety. Cortland,
Gravenstein, Macoun, Northern Spy, Wagener, Wealthy and Winter
Banana are placed under more than one class because of their more or less
extended period of bloom.

30

N. H. Agricultural Experiment Station [Bulletin 274

From this classification of varieties it is possible to pick those apt to
bloom coincidently with the ones needing pollination. Such combinations
should be planted as far as possible, providing cross pollination has been
proven eiTective in such cases. In some instances interplanting two or three
pollenizers is desirable so that pollination will be satisfactory for all. It
may also be wise to plant poUenizing varieties that usually slightly precede
or follow the variety requiring cross pollination, to insure against seasonal
variability in coincidence of blooming periods. Under some conditions it
has been found that varieties hke Northern Spy, which in some sections
bloom so late as to be useless as a pollenizer for Mcintosh, will in a few
locations bloom early enough to be available as pollenizers. Under average
conditions a four or five-day blooming period may be expected with varie-
ties producing flowers as Mcintosh do.

Bees in the Orchard:

There is no doubt that in the majority of orchards, especially where culti-
vation is practiced, the bringing in of honeybees at blossom time will
increase the set of fruit on the trees. It has been proven by observation that
bees are the only important insects for transferring sufficient apple pollen
for commercial orchards. It is true that some flies and even other insects
have a small share in this transfer, but they are never very significant when
a commercial crop is concerned. Even honey bees as individuals fall far
below bumblebees in their efficiency. But a sufficient number of bumble-
bees is seldom found in an orchard. Lack of knowledge of their habits and
failures in attempts to propagate, protect and care for them as is done with
honeybees, indicate that the honeybee alone can be managed properly by the
fruit grower.

It is only the queen bumblebees that are flying about at apple-blossom
time, and the difficulties that befall them during the winter while they hiber-
nate in the grass or under brush or stone walls, cut down their numbers
considerably. Were the bumblebees more plentiful nothing more could be
desired, for they are able to fly about and work at times when the honeybee
is incapable of flight. Wind, low temperature and light rains that preclude
the work of honeybees are no obstacles to bumblebees. Honeybees are not
very active until the air temperature rises above 65° or 70^ F. Rain and
winds also effectively lower their efficiency. At Durham, N. H., bumble-
bees have been seen flying about the apple blossoms when the temperature
was 42' F., a gentle rain was falling and a light wind blowing. Bumblebees
have also been observed to open buds to get inside the flowers.

The usual recommendation is one strong colony of honeybees to the
acre. Perhaps distributing the hives throughout the orchard would give best
results, but placing the colonies in a group in one part of the orchard is
generally satisfactory in smaller orchards an.d means less trouble in caring
for the bees.

Distribution of Pollenizers in the Orchard:

11ie best plan for providing pollenizers is to plant them at the same time
the orchard is planted. The distance between pollenizers is important.
Unless they are valuable commercially, it is often desirable to know the
maximum distance apart that they can be planted and still give satisfactory
results.

June, 1933] PollIxXation and Fruit Setting in the Apple 31

Conditions of the weather in a given section is an important considera-
tion in this respect. Where warm weather prevails at blossom time, the
pollenizers need not be so close together as where the temperature is lower.
Cool weather at blossoming time interferes with bee flight and under such
conditions, which frequently prevail throughout the apple sections of New
Hampshire, pollenizers should be used abundantly. One tree out of every
nine as a poUenizer is the minimum amount to recommend safely. Under
many conditions more pollenizers would be better insurance for a full crop.

Every tree in the orchard should properly be adjacent in some direction
to a pollenizer. In orchards of Mcintosh where pollenizers are present only
in a few spots, it may be noticed that trees adjacent to the pollenizers pro-
duce good crops, and that the crop becomes to a striking degree progress-
ively less on trees farther and farther away. To forestall such results, the
following planting plans are suggested :

If the varieties planted are cross fruitful, such as Mcintosh and Cortland,
one row of Cortland to two rows of Mcintosh would be unquestionable
from the pollination standpoint, unless Cortland were so desirable that the
rows of Cortland could alternate with the Mcintosh rows.

Plan A

Row 1 All Mcintosh

2 All Cortland

3 All Mcintosh

4 All Mcintosh

5 All Cortland

6 All Mcintosh

In this plan (A) it is understood that the trees are all to be permanent.
Planting all one variety in the same row would facilitate keeping the pick-
ers from mixing varieties in harvesting, should the two varieties ripen at
the same time.

,% , ', 1

/V\

Plan B

MMMMMMMMM '"' '

MP M M P M M P M A/i '

MMMMMMMMM A^^^

M M M M M M M M M ;A^ '^

M P M M P M M P M ^'1 ,

M M M M M M M M M ^ '^ '

M^McIntosh or other desired variety.
P^Pollenizer.

In this Plan B for permanent trees, the pollenizers are placed so that
every tree is in contact with one. This number avoids having at least one
tree not adjacent to a pollenizer.

^'^ N. H. Agricultural Experiment Station [Bulletin 274

Where more than one pollenizer is needed to overcome difficulties already
discussed in relation to coincidence of bloom, the following plan may be
considered :

Plan C
Row

1 All Mcintosh or other desirable variety

2 All earlier blooming pollenizer

3 All Mcintosh or other desirable sort

4 All later blooming pollenizer

5 All Mcintosh or other desirable variety

6 All earlier blooming pollenizer

7 All Mcintosh or other desirable variety
Etc.

If a premium is placed on the desired commercial variety, the following
plan may be considered in an orchard of permanent trees :

Plan D

X X X X X X X

X E L X E L X

X X X X X X X

X X X X X X X

X E L X E L X

X X X X X X X

X=Common variety
E^Slightly earlier blooming sort
L^Slightly later blooming sort

In this case there will be two poUenizers to every seven trees of the main
variety. Each tree will also be in contact in some direction with both an
early and a late blooming pollenizer. Likewise each pollenizer will be in
contact in the same way with each of the other varieties.

In case semi-permanent trees are planted in the orchard, some pollenizers
should also be included in the permanent rows. Otherwise the orchard
would be without pollenizers when the semi-permanents are removed.

One of the most satisfactory ways to plant semi-permanents is to follow
the quincunx plan ; that is, plant them where the diagonals between perma-
nent trees cross. Thus :

P P P

\ / \ /
S S

/ \ / \
P P P

P=Pernianent trees

S=Semi-permanents

In this way the trees are crowded the least possible amount, and removal
of semi-permanents is easy.

June, 1933] Pollination and Fruit Setting in the Apple 33

Using two pollenizers, the following plan is suggested :

Plan E
Row

IX 1 2 X 1 2 X — Permanent row

2 XXXXXX — Semi-permanent

3XXXXXXX —Permanent

4 12X12X — Semi-permanent

5XXXXXXX Etc.

6 XXXXXX

7 X 1 2 X 1 2 X

8 XXXXXX
9XXXXXXX

10 1 2 X 1 2 X

IIXXXXXXX

12 XXXXXX

13 X 1 2 X 1 2 X
Etc.

By this scheme if either the permanents or the semi-permanents are con-
sidered separately, the distribution of pollenizers in each is similar to that
in Plan D. When the semi-permanent trees are finally removed, the distri-
bution of pollenizers will then be identical with Plan D.

Naturally many other arrangements of pollenizers are possible, but the
plans described are practical where the goal is high and uniform tree yield
with a minimum amount of pollenizers. They also emphasize the value of
the use of more than one poUenizer.

W^here it is known that the chances for good pollination are exceptionally
favorable, one pollenizer in a block of 16 trees may be sufficient, but ordi-
narily such distribution is risky.

With the orchard layout determined for interplanting pollenizers, the
next problem is the choice of suitable pollenizers.

In Table VII are presented the results obtained in experiments concern-
ing the success of various pollenizers for important varieties of apples. The
data are the result of repeated trials at the New Hampshire and at other
eastern experiment stations.

Data are omitted regarding tests which have not yet been thoroughly sub-
stantiated.

General experience with Baldwin and Wealthy indicates that under New
Hampshire conditions these sorts nearly always set satisfactory crops with
their own pollen. In other sections of the country this has not seemed to be
true, hence these varieties and the Cortland are listed as doubtful. The

34

N. H. Agriculti'ral Experiment Station [Bulletin 274

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June, 1933] Pollination and Fruit Setting in the Apple 35

other varieties have never shown any definite evidence of self-fruitfulness
in the eastern states and should never be planted in very large blocks or in
the total absence of other varieties.

As a pollenizer Baldwin is a complete failure. This is indicated in Table
Vn which shows that with none of our leading New England varieties has
Baldwin given satisfactory results as a pollenizer. Rhode Island Greening
has behaved in a similar way except that it has been found to poUenize
Wagener satisfactorily. The same may be said for Gravenstein. The poor
pollenizing ability of these three varieties is probably due to the poor germi-
nating ability of their pollen and to the large percentage of abnormal pollen
grains which they develop as a result of their unusual genetical make-up.

The other varieties are generally efficient pollenizers, with these excep-
tions : Cortland has not yet proven a satisfactory pollenizer for Graven-
stein. Delicious has failed to show evidence of satisfactorily pollenizing
Golden Delicious or Rhode Island Greening. Mcintosh has not satisfac-
torily pollenized Delicious, Rhode Island Greening or Wealthy. Northern
Spy has not yet caused a satisfactory set of fruit on Delicious or Rhode
Island Greening and Wealthy has failed as a pollenizer for Fameuse and
Rhode Island Greening. Oldenburg and Wagener seem to be outstanding
as good pollenizers for all varieties tested.

In addition to the crosses shown in Table VII Oldenburg has also been
found to pollenize Melba and Lobo well. Melba is self-unfruitful.

With relation to the ability of certain varieties to be successfully pollen-
ized by others, the following may be said : It has been difficult to find many
satisfactory pollenizers for Delicious, Golden DeHcious and Rhode Island
Greening.

Of those shown in Table VII, Cortland, Oldenburg, Wagener and
Wealthy are the only varieties that will pollenize Delicious satisfactorily
beyond any doubt. Golden Delicious seems to be pollenized satisfactorily
by Northern Spy but not by Baldwin or Delicious. Rhode Island Greening
is pollenized well by Cortland and Oldenburg.

Finding suitable pollenizers for the remaining varieties has seemed less
difficult.

In addition to failure to respond to pollination by Gravenstein and Rhode
Island Greening and Baldwin, Delicious has failed to give a satisfactory
set when pollenized by Mcintosh ; Gravenstein by Cortland.

Wagener is unusual in that Gravenstein and Rhode Island Greening have
proven satisfactory pollenizers for this variety while Mcintosh has failed.

Certain variety mixtures are not to be considered in relation to their
pollenizing qualities because of the small chance of the period of bloom
coinciding under New Hampshire conditions. Such relationship exists
between Golden Delicious and Gravenstein, Golden Delicious and Mcin-
tosh, Gravenstein and Northern Spy, and Mcintosh and Northern Spy.

Fortunately, among a few varieties interfertility exists. The following
lists indicate first, cases where two varieties may be planted together and
each will satisfactorily pollenize the other ; and, second, cases in which two
varieties are inter-sterile and neither will pollinate the other.

To illustrate inter-fertility of two varieties, it may be seen from Table
VII that in many cases where two varieties are concerned, each pollenizes
the other satisfactorily. Thus one may have a Cortland orchard inter-

36 N. H. Agricultural Experiment Station [Bulletin 274

planted with Delicious and expect a good commercial crop on both varieties.
Other varieties that prove satisfactory when planted alone with Cortland
are Mcintosh, Northern Spy and W^ealthy.

Delicious may be interplanted with any one of the following varieties and
both will set a good crop : Cortland, Oldenburg, Wealthy, Yellow Trans-
parent.

Similarly Early Mcintosh and Wealthy are inter-fruitful, as are Fam-
euse and Mcintosh, and Gravenstein and Wagener.

Mcintosh is inter-fruitful with each of the following varieties : Cortland,
Fameuse, Oldenburg, Wealthy, Yellow Transparent.

Milton is inter fruitful with Wealthy.

Northern Spy is interfruitful with Cortland, Golden Delicious, Olden-
burg and Wealthy.

Wagener is inter-fruitful with Delicious and Gravenstein.

Oldenburg is inter-fruitful with Delicious, Mcintosh, Northern Spy and
Wealthy.

W^ealthy is inter-fruitful with Cortland, Delicious, Early Mcintosh,
Mcintosh, Milton, Northern Spy and Oldenburg.

Yellow Transparent is inter- fruitful with Delicious and Mcintosh.

On the other hand, in some combinations, two varieties may be planted
together and neither can successfully pollenize the other. Naturally such
combinations should be avoided unless other varieties are planted as pollen-
izers. They include the following : Baldwin and Rhode Island Greening or
Gravenstein ; Cortland and Gravenstein ; Delicious and Rhode Island
Greening ; Gravenstein and Baldwin or Cortland ; Mcintosh and Rhode
Island Greening; Northern Spy and Rhode Island Greening; Rhode Island
Greening and Baldwin, Delicious. Mcintosh, Northern Spy or Wealthy;
Wealthy and Rhode Island Greening.

From this list the following combmations would be recommended where
desirable, because of coincidence of time of bloom and superior commercial
quality :

Cortland and Delicious
Cortland and Wealthy
Delicious and Wagener
Delicious and Wealthy
Gravenstein and Wagener
Mcintosh and Cortland
Mcintosh and Wealthy
Northern Spy and Wealthy

Often the choice of varieties is such that a third or occasionally even four
or more varieties need to be inter-planted to satisfy all needs for pollina-
tion. As an example of the latter, if Gravenstein, Baldwin, Delicious and
Mcintosh were the varieties to be planted in the orchard, all except De-
licious would be properly taken care of as far as pollenizers are concerned.
To insure a full set on Delicious, some other variety, such as Cortland,
Wagener or Wealthy, would also have to be planted in the orchard.

If Rhode Island Greening, Gravenstein, Baldwin and Delicious were the
varieties desired for the commercial crop, it would be necessary to intro-
duce pollenizers for Delicious and Rhode Island Greening. Cortland is the

June, 1933 J Pollination and Fruit Setting in the Apple 37

only variety which has sufficient data tn recommend it in this case. The
capability of untested varieties as poUenizers for Rhode Island Greening
can only be conjectured.

Usually it is advisable to interplant three varieties, or one variety and
enough trees of two other varieties to insure cross-pollination and set of
fruit^

Some of the better combinations and the reasons for choosing them are
given below :

Earlier-blooming desirable orchard varieties capable of poUenizing
Mcintosh are not easy to find. Wagener blossoms early enough and the
period of l^loom is ample so that one need not worry about the blooming
periods not coinciding. Delicious is a desirable second sort because it will
pollenize both Mcintosh and Wagener. Another good triple combination is
Mcintosh, Cortland and Delicious. These combinations satisfactorily over-
come any possible difficulty due to lack of coincidence of l)loom or ability
to pollenize.

When Northern Spy is desired in the orchard, the latest blooming sorts
are necessary as poUenizers. Under New Hampshire conditions Mcintosh,
although known to be able to cause a set of fruit on Spy, is not practical
as a poUenizer for this variety under orchard conditions because Mcintosh
bloom is usually over before Spy buds begin to open. The same may be
said for Delicious bloom.

The extended period of bloom of Wealthy, however, normally makes it
dependable for pollenizing Northern Spy. The two are inter-fruitful.
Golden Delicious also blooms late enough to reach Spy and fortunately the
two are inter-fruitful. Since Mcintosh and Wealthy are inter-fruitful, a
combination of Northern Spy, Mcintosh and Wealthy might under some
conditions prove a favorable one. Baldwin and Delicious might also be in-
troduced to make the harvest season more continuous.

Where Gravenstein is a profitable variety, Oldenburg and Wagener are
good poUenizers. Mcintosh would also fit well into such an orchard.

Many other combinations are possible, but the following questions should
be remembered and considered in choosing poUenizers :

1. Do the known statistics indicate that the varieties desired as poUeniz-
ers are able to cause a set of fruit on the commercial sort to be planted ?

2. How well do the periods of bloom of varieties and poUenizers overlap ?

3. Is it important to consider the commercial value of the poUenizers ?

4. Are the poUenizers regular annual bearers ?

5. Are they hardy and highly resistant to frost damage?

6. Are they free from and resistant to such diseases as canker, apple
scab, blight, etc. ?

7. Are the poUenizer varieties suspectible to railroad worm ?

Reworking Orchards to PoUenizers:

After one finds that an older orchard contains certain varieties which
have become unprofitable, their replacement by better sorts is desired. Be-
fore top-working the undesirable sorts one should consider whether their
disappearance will constitute at the same time the removal of necessary pol-

38 N. H. Agriculture Experiment Station [Bulletin 274

lenizers. In such a case, the data previously presented may be consulted in
selecting suitable pollinating sorts to topwork in the orchard.

In many cases the varieties are interplanted in such a way that the
permanent rows consist entirely of one variety, no recognition having been
taken at the time of planting of the necessity for permanent pollenizers.
After removal of the other semi-permanent pollinating varieties, such an
orchard will usually be found to set little fruit. The remedy then is to top-
work certain of the trees to pollenizers. It will still be several years, how-
ever, before the grafts bloom.

In top working an orchard, it is advisable eventually to work over a tree
completely to the pollenizing variet}', rather than to graft only a portion of
the tree permanently. When a tree is only partially worked over, either
through accident or neglect, the pollenizing section of the tree may be lost.

Temporary Relief from Lack of Pollenizers:

As soon as one learns that lack of pollenizers accounts for the failure of
an existing orchard, a crop may be obtained if bees are present, by placing
blossoming branches of pollenizing varieties in buckets or tubs of water
throughout the orchard or near the hives of bees. Foreign pollen is thus
available for the flowers on the trees and will tide the orchardist over the
period during which grafts are becoming old enough to produce bloom.

Summary

1. The increasing importance of planting only certain varieties of apples
in orchards has led to the problem of cross-pollination.

2. Flower-bud formation and the relation of various flower parts to suc-
cessful fruit setting are important.

3. Under New Hampshire conditions where Mcintosh is a leading com-
mercial variety, pollination has become important because of the self-
unfruitfulness of this variety.

4. The position of the flower in the cluster has a profound efifect on the
percentage of flowers that set fruit and on the size and shape of the result-
ing apples.

5. Competition between flowers and fruits for food and water has a pro-
found effect on the number of fruits reaching maturity. The nutrition of
the tree is very important in this respect.

6. Certain varieties such as Baldwin, Gravenstein and Rhode Island
Greening are rather poor pollenizers, partly because of the low germinating
power of the pollen of these sorts.

7. Certain varieties do not make good pollenizers for other varieties
when their dates of bloom are widely separated.

8. Bees are of inestimable value to the orchardist.

9. For economy, a careful consideration of the arrangement and distri-
bution of pollenizers is important.

10. When orchards have proven unfruitful because they have been
planted in solid blocks, pollenizers should be grafted into some of the trees.

11. Temporary relief from a lack of pollenizers is available through the
introduction of bouquets of other varieties at blossom time.

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