403
AGENCY OF INSECTS IN FERTILIZING
PLANTS.

BY W. J. BEAL.

(Concluded from page 260.)
THERE are two other peculiarities among certain plants
by which a cross-fertilization is made most probable, and
even very sure in some cases, notwithstanding the flowers
are all perfect and of one form.
In some of these the stigmas come out and are fertilized before the anthers of the flower burst open; while in

404
others the anthers are in advance, and discharge their
pollen before the stigmas appear. In either case the
flowers act as though they were monœcious.
These peculiarities have been termed dichogamy by
Sprengel, who made the discovery many years ago. Of
the first kind, in which the stigmas are in advance of the
anthers, I examined the young flowers of several species
of Spiræa, just before any of the anthers had opened, and
in all I found the stigmas quite plentifully covered with
the yellow powder. Many stigmas were dry and withered, while some of the anthers were still full of fresh
pollen. Similar observations were made upon False
Solomon's Seal, several species of Potentilla, Plum,
Cherry, and others. One of the best examples of this
kind was pointed out by Dr. Gray, in the case of the
Plantain or Ribgrass (Plantago lanceolata Linn.), a
troublesome plant which is too rapidly finding its way
into meadows and waste places.

These flowers, in arrangement, somewhat resemble a
short tapering spike of Timothy or Herd's-grass. The
long hairy stigmas come out first at the base of the spike,
and are quite withered and dead before the stamens of the
same flowers appear in sight. By the time the long
thread-shaped stamens of the lowest flowers hang out their
anthers, the stigmas of other flowers higher up the spike
are exposed and ready to receive the fertilizing element.
So new pistils continue to come forth, keeping in advance
of the stamens. The long filament raises the anther so
high that it is brought near the stigmas of younger flowers farther up the spike. This plant, like most of the
large Grass-family, is not visited by insects, as it secretes
no nectar, but each anther is hung on a mere point (versatile) and every slight motion of the air keeps it fluttering.

405
By applying a low magnifying power, the pollen
was seen with its long tube thrust into the stigma before
anthers had shown themselves above the calyx. While
within the calyx the filaments are folded upon themselves,
which accounts for their great length as soon as they come
forth.

The Broad-leaved Plantain (Plantago major Linn.), so
common about door-yards, resembles the one above mentioned as regards its mode of fertilization.

On the long spikes of flowers of the False Indigo and
Lead-plant (Amorpha fruticosa Linn., and A. canescens
Nuttall), the bees and wasps were seen beginning at the
base on the older flowers, and so passing up, visiting
those above in which the anthers were still young and
enclosed by the corolla. Here, as in the Plantain, the
pistils are a day or two in advance of the stamens,
and the insects are a means of affecting a cross-fertilization.

The common Dandelion (Taraxicum dens-leonis Desfotaines) is a good example of the other kind of dichogamy,
in which the anthers discharge the pollen before the stigmas are ready to receive it. This belongs to a very large
family called Compositœ, which contains from one-eighth
to one-tenth of all the flowering plants in this part of the
world. Each yellow head in the Dandelion is a cluster
of small flowers packed closely together, and not one
large compound flower as the name implies, which was
given by the early botanists. Each pistil bears two long
slender stigmas surrounded by the anthers which are
united by their edges, forming a tube (syngenesious).
The stigmas are covered on the outside with small hairs,
having their tips pointing upwards, like the beards on a
head of barley.

406
Imagine a head of barley much lengthened and split
in two down the middle, and you have a good representation of the stigmas of a Dandelion. When the tips of
these are just above the apex of the anthers, the pollen is
discharged and carried up on the hairs by the style which
grows very rapidly at this time.

The stigmas are closely pressed together until clear
above the anthers, when they begin to spread and roll
back, exposing the inside surface which alone is sensi-
tive to the action of the pollen. Several kinds of bees,
flies, and smaller insects visit these flowers and brush the
pollen off the outside of the style, and leave some on the
inside surface where it can take effect. Were it intended
for close, self-fertilization, as a superficial examination
would seem to indicate, the style should be shorter, and
the stigmas a little separated, so that pollen would meet
the proper surface before the stigmas leave the surrounding anthers. Or else the surface, which is sensitive
to pollen, should be on the outside instead of on the in-
side.

I have examined Coreopsis, Fall Dandelion (Leontodon), and Succory, and many more of this vast family,
which showed these same peculiarities mentioned above.
In Sweet Coltsfoot (Nardosmia), a rare plant of this
order growing north of this latitude, some of the little
flowers are sterile, i. e., the imperfect pistil bears no
seed, but the top of the style has a tuft of little hairs
which push up the pollen from the anther-tube that it
may reach the stigmas of other flowers, and so not be entirely lost.

At the suggestion of Dr. Gray I examined some half a
dozen or more species of Bellflower, or Campanula. The
one most carefully noticed was Campanula rapunculoides.

407
It has five anthers which stand up close together, although
not joined by their edges into a tube as in the dandelion.
In three other respects it resembles this plant; namely,
in having the style covered with hairs or short bristles on
the outside, and in having the sensitive part of the stigma
on the inside. In the same way also the style nearly
doubles in length after the pollen is discharged.

The pollen begins to discharge very soon, so that by
the time the corolla is fairly open, the anthers wither,
and are coiled up at the base of the flower. After the
hairs on the style have nearly all disappeared, and the
pollen which they held has been removed, or has turned
brown in decay, the stigmas separate at the top, and expose the sensitive surface. For each flower to be self-
fertilizing, this plan is a perfect failure.

Bees are willing agents here, as in other instances,
alighting first on the stigmas of the oldest flowers, which
are farthest down the stem, and then passing up to others
which are younger. Besides collecting nectar at the bottom of the flower, they collect the pollen by scraping
the style upon each side with their legs, and, when call-
ing at the next flower, first strike the exposed stigmas,
leaving a few little morsels as tribute for their bountiful
supply.
The flowers of the Mallow Family have numerous stamens, joined into a column or tube (monadelphous),
through which the stigmas are protruded. My observations on this family have been rather limited, but in the
High Mallow (Malva sylvestris Linn.), the anthers all
burst, and very little pollen remains about the flower,
when the stigmas first come to the light, as brides too late
for the marriage, for the bridegrooms have been carried
away by the priests, and perhaps wedded to others.

408
The fact once well established, that insects are necessary to fertilize plants, brings up some other interesting
inquiries in reference to the origin of animals and plants.
Some would probably say that plants, which now require
the agency of insects, have arrived at their present form
by a long series of gradual changes, and that before the
proper insects were created they were capable of self-
fertilization. Others may say that the plants of this
structure were created later than those capable of self-
propagation, and upon which the insects could subsist for
a time. Another plan can, however, be devised, as they
are alike useful to each other. "As the bow unto the cord
is," they may have been called into existence at the same
time, the flowers to secrete nectar for the insects, and the
insects to fertilize the flowers.

Were Dr. Watts again alive, and should some one tell
him these facts of science, he might well exclaim, as the
Queen of Sheba did 'to King Solomon, "Behold the half
was not told me." He gave us but half the story, and
that the one which teaches the least instructive lesson.
It is now over two years since some one, I wish I knew
his name, rung the change,-

"How doth the little busy bee,
Improve each shining hour,
By carrying pollen day by day,
To fertilize each flower."

The bees go buzzing through the air visiting flower after
flower, not only to get their daily bread, but render an
essential aid in perpetuating the existence of the very
same plants which furnish them food.
This furnishes another pertinent illustration of the
mutual dependence of the animal and vegetable kingdoms.