AGENCY OF INSECTS IN FERTILIZING PLANTS.
BY W: J. BEAL.

MR. CHARLES DARWIN and other botanists have proved
beyond a doubt, that some flowers, in which the pollen
may easily gain access to the stigma of the same flower,
are sterile unless fertilized by pollen borne from other
flowers, while many are much more productive by a cross
fertilization.
For information concerning the peculiar manner in
which fertilization is effected in the Balsam, Wood-sorrel,
Violets, Dicentra or Dielytra, Corydalis, Mitchella or
Partridge-berry, Oldenlandia or Houstonia, Primrose,
Barberry, Lysimachia or Loosestrife, Orchids, Dutchman's
Pipe, and others ; consult the observations recorded by
Mr. J.T. Rothrock in the second number of the NATURAL-
IST, Mr. Darwin's work on the "Fertilization of Orchids,"
and seven articles by Dr. A. Gray in the "American Ag-
riculturist," beginning in May, 1866.
With the fact that insects are necessary to fertilize some
plants, and the theory that all are improved by crossing,
let us see how this is accomplished in plants which may
not seem to require the aid of the wind or insects. Plants
are very rarely found in which the pollen may not, occa-
sionally at least, get to the stigma of another flower of the
same, or an allied species. Then if the pollen is "pre-
potent" or most effective on stigmas when thus transferred,
a cross is very sure to result, even though much pollen
comes in contact with the stigma of the same flower. Dr.
Gray, acquainted with these facts, and familiar with the
structure of the Iris, saw that insects must be needed for
the fertilization of this plant also, and without seeing the
bees upon them, shrewdly pointed out the manner in which

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they must carry the pollen from one flower to another.
We verified his theory by observations made two years
ago, and found it to be true in the essential particulars.
Without giving a scientific description of the flower, it
is enough for our present purpose to say, that the parts
consist of three curved tubes, each just about large enough
to admit a common honey-bee, being a trifle larger than
a cell in her comb.
There is a showy crest, or attractive platform, projecting
at the outer end of each tube upon which the bee first
alights. When going into the flower for the first time
during the day, she is free from pollen. She brushes
against a lid which hangs from above, not unlike an old-
fashioned swinging door of a cat-hole, as sometimes seen
about barns or corn-cribs. When farther in beyond the
lid, she comes against the anther, which only discharges
pollen on the side next to the bee's back. After getting
what nectar she can at the lower end of the tube, she
backs out again, pushing the trap-door in the opposite
direction. The outside of this door is the only part of
the stigma upon which the pollen will produce any effect,
so upon visiting the first tube no pollen adheres to the
sensitive side of the stigma, although the bee leaves the
place with her back well powdered. Calling at another
tube, she dives in as before, this time dusting the outside
of the lid with pollen which was brought from the tube
first visited.
In the early part of June, I examined the common Blue
Flag (Iris versicolor Linn.) at different times during the
day, and always succeeded in seeing the bees at work
while their heads and backs contained an abundance of
pollen. In wilted flowers, and in some that were fresh,
I saw bees occasionally get in and out at the side of the

256
tube, without touching the stigma at all. Sometimes
they went in the tube as first described, and then slipped
out at the side instead of backing out. Several went on
top of the flower and tried to find other ways to get at the
sweets below, but in every instance they failed, and soon
left that position.
At the Botanical Garden, Cambridge, Mass., I noticed
bees on several foreign species of Iris, in some of which,
as Iris pseudocarus of Southern Europe, the tube is more
nearly perfect, so that it is impossible for them to find a
side entrance or egress.
The corolla of Andromeda floribunda Pursh, is nearly
urn-shaped, hanging with the open end or entrance down.
The ten long anthers open at the apex by two round
holes, and each anther is supplied with two horizontal
or reflexed awns on the outside next the corolla. The
stigma is just at the narrow mouth of the corolla. . Bees
in abundance visit the flowers, thrusting their long tongue
or proboscis against the awns or horns of the anther, as
they reach in for nectar which is secreted farther on. By
hitting the awns the anthers are disturbed, and the holes
brought close against some part of the bee's probos-
cis, which is well sprinkled over with pollen, as well as
the other mouth parts hanging below the flower. Bees
were examined, and found to have the parts mentioned
covered with the four-grained pollen which is peculiar to
a few plants.
I cannot see how pollen alights on the stigmas of this
plant, for in falling out in the natural way it must pass by
to the ground. But the insect puts the material in place
every time as effectually as a mason can stick mortar on
the ceiling of a room. The Blueberry ( Vaccinium) is
similar in structure to the Andromeda, except that the

257
awns are wanting. Probably most flowers which droop
or hang down are fertilized by insects. For otherwise,
how can the pollen find the tip of a stigma, when the
style is suspended?
The mode of fertilization in the American Laurel (Kal-
mia) has already been well described in the NATURALIST,
but I may be excused for adding my testimony concern-
ing this beautiful and interesting plant.
When the anthers are liberated from the pockets in the
corolla, the stamens suddenly straighten and throw jets
of pollen often for a foot or more, "acting," as Professor
Gray used to say, "like a boy's pea-shooter."
Many times when the dew was on, I have seen the
common honey-bee and other Hymenoptera about these
flowers. When the bee alights on a flower, the style
comes up between the legs where they join the body, or
sometimes farther back against the abdomen.
In this position they turn around, as though they were
balanced on a pivot, generally inserting the tongue out-
side of the filament, and, while doing this, pull the sta-
mens with their legs towards the centre of the flower, re-
leasing them and frequently receiving the shots of pollen
on their own body. A single visit from an insect is suf-
ficient to release all the anthers. By noon it was a diffi-
cult matter to find a flower which had not been visited in
this way. Insects seem to be absolutely necessary for
the perfect fertilization of Kalmia angustifolia and K.
latifolia, for I tied small nets over some flower-clusters
(corymbs), and found that when the bees were kept away,
the flowers withered and fell off, most of the anthers still
remaining in the pockets, and the filaments so decayed
that their elasticity was entirely gone. The very few an-

258
thers liberated were probably brought out by the shaking
of the bushes by the wind.
Considerable pollen was found stuck on the corollas by
the nectar, which was uncommonly abundant, as no in-
sects of much size were allowed to remove it. The wind
might have carried some of this pollen to other flowers,
or it might have dripped from those above to flowers be-
low in drops of water (there were two showers during
these experiments); but I infer this was not the case in
the examples mentioned, because the flowers, especially
the stigmas, remained fresh much longer than those
which were left exposed to the visits of insects.
The flowers of several Honeysuckles, of the Mustard
Family (Cruciferæ), of the Bladder-nut (Staphylea tri-
folia L.) were noticed, and in each case the conclusion
reached was, that the chances are better for cross fertil-
ization than otherwise.
The long cylindrical, bell-shaped corollas of the Purple
Foxglove (Digitalis purpurea) are much visited by bees.
The flowers are mostly obliquely suspended, and in all
thus situated, the stamens and style are close to the up-
per side of the corolla. The insects alight at the opening
of the corolla, on the side opposite the stamens. This is
generally the lower side as the flowers hang, then reach-
ing above, they catch hold of the style and stamens, and
crawl in with the back down, brushing the whole length
of the underside of the body, first against the stigma,
and, farther on, against the anthers.
They seem unable to get into the flower without catch-
ing hold of the stamens, and it is often with considerable
difficulty that they enter at all, for they are obliged to
hold on to the edge with the hind legs until they can
catch the stamens with their fore legs.

259
In the Evening Primrose ( Oenothera glauca Michx.,
Oe. Missouriensis and linearis Michx.), the stigmas pro-
ject beyond the anthers, and the flowers vary from an erect
to a horizontal position.' There are four large stigmas for
each style, spreading in the form of a Greek cross.
The pollen, slightly held together by delicate threads,
is collected in the morning by great numbers of small
wasps, about two-thirds the size of honey-bees. I have
often watched them while coming down on, or just over,
the stigmas, leaving pollen as they went in, and after col-
lecting what they could, fly out at the side without touch-
ing the stigma. On one of these plants, at two different
times, a wasp was eagerly trying to pick up the pollen
which had been left on the stigmas; the more they tried
to collect, the more they scattered pollen about on the
glutinous surface, until, as if discouraged or disgusted,
they rapidly cleaned their legs of all the tangled mass,
and flew away, leaving that cluster of flowers entirely.
In the flowers of the Pea, False Indigo, Yellow-wood
(Cladastris), Red-bud or Judas-tree, Red and White
Clover, Locust, and others of this large and important
family (Leguminosæ), the anthers surround the stigma,
and are closely covered by the corolla. This certainly
looks like a very clear case for self-fertilization, but I
doubt not the reverse is very often the case. Many
of the flowers, as the Pea and Locust, have one petal
much larger than the rest, called the standard or banner.
Opposite this is another part composed of two petals
sometimes united, termed the keel. On this keel bees
uniformly alight, and crowd the head down next to the
banner-petal. To enable them to do this, they kick
the keel and side petals (wings) with their hind legs,
and push them back so that the anthers and stigmas

260
come out from their concealment and meet the underside
of the insect where pollen may be left or received. Why
the style should be so uniformly curved upward, and all
should be brought against the abdomen of insects, I can-
not well conceive, unless it be of some use to the plant.
Lupine, another species in this family, has a remarkably
long keel which makes a close sheath for the inside parts.
On the style, just below the extremity, is a circle of long
stiff bristles. As the keel is pushed down, only the stig-
ma, with the bristles below, appears outside, and this
pushes out a mass of pollen which generally hits some
part of the insect. When left, the flower resumes its
former position again.
For about six times pollen can be pushed out in this
way, when the supply becomes exhausted. Insects begin
on the lowest flowers, and so go up the spike to others
which are higher and younger. No experiments have
been made on Lupine to show whether it will produce
more seeds when visited by insects than when protected.