POLLEN
“In a few days, even in a few hours, a flower withers. Petals, calyx,
stamens fade and die. Only one part survives: the ovary, which is to
become fruit. Now, in order to outlive the rest of the flower and
remain on its stem when all else dries up and falls, the ovary at the
moment of blossoming, receives an access of vigor, I might almost say a
new life. The magnificence of the corolla, its sumptuous coloring, its
perfume, all serve to celebrate the solemn moment when this new
vitality is awakened in the ovary. This great act accomplished, the
flower has had its day.
“Well, it is the dust of the stamens, the pollen, that gives this
increase of energy without which the nascent seeds would perish in the
ovary, itself withered. It falls from the stamens on to the stigma,
which constantly wears a sticky coating designed to hold it; and from
the stigma it makes its mysterious influence felt in the very depths of
the ovary. Animated then with new life, the nascent seeds develop
rapidly, while the ovary swells so as to give them the nourishment and
the space they require. The final result of this incomprehensible
travail is the fruit, with its contained seeds all ready to germinate.
“Let us cite a few of the numerous experiments that prove the absolute
indispensability of pollen.
“Most flowers have both stamens and pistils; but there are plants that
have their stamens and pistils in separate flowers. Sometimes the
flowers with stamens only and those with pistils only are found on the
same plant; sometimes they are found on separate plants. Plants having
flowers with stamens only and flowers with pistils only on the same
stock are called monœcious plants. This expression means ‘living in one
house.’ The flowers with stamens and those with pistils do indeed live
together in the same house, since they are found on the same plant. The
pumpkin, cucumber, melon, hazel-nut-tree are monœcious plants.
“Where flowers with stamens and those with pistils are found on
different stocks, the plants are termed diœcious; that is to say, they
are double-house plants. Hemp, the locust-tree, and the date-tree are
diœcious.
“It is especially in monœcious and diœcious plants that the pollen’s
indispensability is plainly manifest on account of the natural
separation of the stamens and pistils. Let us take for example the
locust, a tree of extreme southern France, bearing seeds in pods
similar to those of the pea, but brown, very long, and very wide, and
containing in addition to the seeds a sugary pulp. Supposing we took a
notion, if the climate permitted, to grow locust seeds in our garden,
what locust tree must we plant? Evidently the one with pistils, because
it alone produces the ovaries that become fruit. But that is not
enough. Planted by itself, the locust tree with pistils will indeed
blossom profusely every year, but will never in all eternity bear any
seeds, for its flowers will fall without leaving a single ovary on the
branches. What is wanting? The action of the pollen. Near the locust
with pistils let us plant one with stamens. Now fructification proceeds
as we wish. Puffs of wind, insects that pilfer from one flower and
carry to another—these convey the pollen from the stamens to the
stigmas, the torpid ovaries spring to life, and the locust pods grow
and ripen perfectly. With pollen, seeds; without pollen, no seeds.
“Another example. In spots of fertile land in Northern Africa, spots of
land called oases, the Arabs cultivate numerous date-trees which
provide them with dates, their principal food. Date-trees, too, like
the locust, are diœcious. Now, in the country of the date-tree, a sandy
plain parched by the sun, spots of watered and fertile land are rare
and have to be turned to the utmost possible account. Accordingly the
Arabs plant only date-trees with pistils, the only ones that will
produce dates. But when they are in flower, the Arabs go long distances
to fetch bunches of blossoms with stamens from wild date trees in order
to shake the pollen on the trees they have planted. Without this
precaution there is no harvest.
“But I am coming to an example that will be more familiar to us. The
pumpkin is monœcious: flowers with stamens and flowers with pistils
inhabit the same house, the same vine. Before they are full-blown they
can easily be distinguished from each other. The flowers with pistils
have under the corolla a large swelling which is the ovary, the future
pumpkin. The blossoms with stamens have not this swelling. Well, from
one pumpkin vine standing apart in the garden let us cut off all the
buds with stamens before they open, and leave those with pistils. For
greater surety we will wrap each one of these latter in a piece of
gauze large enough to let the flower develop without hindrance. This
operation must be carried out before the buds open, in order to make
sure that the stigmas have not already received any pollen. Under these
conditions, not being able to receive the vivifying dust, since the
flowers with stamens are cut off, and since also the gauze wrappings
keep out the insects that might bring the pollen they had pilfered from
some neighboring pumpkin vine, the pistillate flowers will wither after
languishing awhile, and their ovaries will dry up without growing into
pumpkins. If, however, we wish any selected blossoms to fructify in
spite of their gauze prison and the suppression of the staminate
blossoms, we take a small camel’s hair brush and gather a little pollen
which we put on the stigma. That is enough, the pumpkin will come.
“The absolute necessity of pollen for the formation of fruit explains
to us the harmful effect of violent winds and prolonged rains in
blossoming time. Swept away by blasts of wind, or washed away by rains,
or simply spoiled by long-continued moisture, the dust of the stamens
no longer acts on the ovaries, and the flowers fall without
fructifying. This ruin of the harvest from lack of pollen is known as
blight.”