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-
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
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
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
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
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.
N. H. Agricultural Experiment Station [Bulletin 274
1 — 1
1 — 1
June, 1933J Pollination and Frtit Setting in the Apple 29
Because of the scarcity of bunibleliecs, tliis unusual procedure is not
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
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
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
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.
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
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
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.
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
MMMMMMMMM '"' '
MP M M P M M P M A/i '
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.
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
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
If a premium is placed on the desired commercial variety, the following
plan may be considered in an orchard of permanent trees :
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
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
\ / \ /
/ \ / \
P P P
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 :
IX 1 2 X 1 2 X — Permanent row
2 XXXXXX — Semi-permanent
4 12X12X — Semi-permanent
7 X 1 2 X 1 2 X
10 1 2 X 1 2 X
13 X 1 2 X 1 2 X
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-
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