MARRIAGE CUSTOMS OF PLANTS
“_Pale primroses
That die unmarried._”--_Shakespeare_
“Love consumes the plants” once wrote Linnaeus, and the observation of
every student of Nature goes to confirm his statement. The plants marry
and are given in marriage. Reproduction is undoubtedly their chief end
in life.
The simplest and most primitive plants have no sex but produce new
individuals by splitting their single cells in two. It is in the
thread-like bodies of Pond Weeds that we find the first beginnings of
the principle of generation by union. These lowly creatures consist of
single cells strung end to end like beads in a necklace. When two of
the living chains happen to find themselves parallel to each other,
certain of the cells reach out and join those opposite them to form new
cells. Such a mixture of life forces is always beneficial to the race.
In the higher plants the same process is carried out in a little more
elaborate way. Of the two cells which unite, one is small and active,
and is called the male or pollen cell. The other is larger, richer and
more passive, and is the ovule or female cell.
It is one of the main objects of each plant’s life to see that its
ovules are fertilized by pollen grains from some other member of
the same species. When this is impossible, flowers are reduced to
fertilizing themselves, but if this continues very long, degeneracy is
very apt to result. It is not wise to marry one’s first cousin.
Many plants depend upon the wind to distribute their pollen. Such
species bear slight, inconspicuous flowers which not infrequently
cluster together in long, pendent catkins. This was undoubtedly the
first and original form of plant marriage. Though often successful, it
is very wasteful and undependable. “The wind bloweth where it listeth”
and loses a million grains of pollen for every one it lodges.
One hazy day in the long ago, some plant had a brilliant idea. “There
are a number of insects which are in the habit of paying me unwelcome
visits for the purpose of eating pollen. Why can’t I make use of these
thieves and turn their marauding habits to my own advantage?”
No sooner said than done, though it doubtless took many centuries
to get the plan in thorough working order. It was a new departure
in the plant world and led to various revolutionary changes. In all
probability, there were no bright-hued flowers before the advent
of pollen-eating insects. In the beginning, at least, flowers were
developed as the signs by which plants advertised their wares. “We will
make ourselves luringly attractive,” reasoned the plants. “We will add
to our bright-coloured petals the sweet delights of nectar and honey.
While the insect is eating at our table, we will shower his back with
pollen and, going forth to some floral neighbour, he will unwittingly
become the marriage priest of our race.”
This was the idea, and in many diverse and wonderful ways the plants
have carried it out. The first flowers were developed by training
certain stamens to flatten and expand themselves, daub their surfaces
with colour, and so become petals. This evolutionary fact can be
seen today in the white Water Lily, where concentric rows of stamens
gradually merge into petals. Double Roses and Poppies are examples of
the same thing.
The formation of flowers was only the first step. It is not enough to
get the insect to come to the plant. Once he is there, means must be
found to make sure that he performs the marriage duties assigned to
him. Each flower takes care of this problem in a different way.
At ordinary times, the Gorse is a closed flower, provided, however,
with a little step or platform on which a Bee can alight. As soon as
an industrious honey-seeker has settled down on this little floral
porch, his pressure causes the entire corolla of the flower to spring
violently open and shower him with pollen. A Gorse flower which has
thus unburdened itself at once hangs down dejectedly and is no longer
the object of insect regard. The Lupine and the English Bird’s-Foot
Trefoil entertain their tiny visitors in a similiar way.
There are two different arrangements of sexual organs in the Primrose.
One variety is provided with long stamens and a short pistil. The
other has the reverse combination of short stamens and a long pistil.
In both cases, the nectar is in a pit at the bottom of the flower. As
long as an insect visits short-stamened flowers, he collects pollen on
the upper part of his proboscis. Happening to enter a short-pistiled
flower, this portion of his drinking tube is now opposite the
female organ and fertilizes it. In the same way, the insect’s feet
gather pollen from the long-stamened flowers and deposit it in the
long-pistiled variety. By such involved methods does this particular
flower make sure of fertilization.
Sage flowers have only two stamens but they do the work of forty. Using
their power of movement, they bend forward and deliberately embrace a
bee as soon as he enters their chamber. They do not release him until
he is covered with their yellow pollen.
The English Figwort has adopted repulsive methods of entertainment.
It has contrived to make itself look like and give forth the odour of
decaying meat, because it knows that it will thereby attract certain
Wasps. The South African Stapelia does the same thing with the idea of
alluring Carrion Flies. Still another imitator of similiar kind is the
pale-green Carrion Flower whose visitor is the Blow Fly.
When in repose, the stamens of the pink-white Mountain Laurel (_Kalmia
Latifolia_) curve so that their anthers or pollen-bags fit into
corresponding pits or depressions in the petals. When a Bumble Bee
happens along and blunders among these delicate organs, the stamens
spring up and shower his back with pollen.
Everyone is familiar with the purple barber pole of the Cuckoo Pint
which stands up straight out of a pulpit-shaped leaf. This barber pole
is the upper end of a fertilizing device of marvelous efficiency.
Down in the shelter of the cup-shaped leaf, the pole is covered with
primitive male flowers, without petals or without sepals, in fact,
nothing more than simple stamens. Below them are rudimentary female
flowers consisting of unadorned pistils. Certain Midges and Flies are
attracted into the leaf cavity of the plant by the store of sweets at
its bottom. Traveling down the pole, these would-be feasters readily
pass the guardian hairs just above the stamens, pass the stamens
themselves and unintentionally fertilize the pistils with pollen they
have picked up on other marauding expeditions. Having partaken of
honey, the Flies seek to escape, but now find the way barred by the
down-pointing hairs which have bristled up in a militant manner. The
insects must stay until the plant decides to release them, which is
never until the stamens have ripened and showered them with a fresh
supply of pollen.
The Orchids are among the most beautiful and extraordinary flowers
in the world. Their noteworthy development has come about through
their efforts to secure abundant and efficient insect fertilization.
So certain are their methods that they ordinarily do not require the
services of more than one stamen.
In one variety, the English Spotted Orchid, the pollen is enclosed in
two sacks or bags provided with long stems. These sacs are lodged in
special cavities near the pistil in such a manner that the sticky ends
of the stems come in contact with the head of a nectar-sucking Bee.
They adhere firmly. When he departs he has two bulbous ornaments for a
crest. At first they stand erect, but as he flies, the air dries them
and they incline forward on curved stems. When he is ready for his
next cup of honey, they are hanging down in front of his eyes like a
new kind of pawnbroker’s sign. It is no mere happenstance that in this
new position the pollen sacs are deposited on the stigma of the second
flower’s pistil. By such ingenious marriage customs, the Orchids have
become a dominant family in plantdom. They are in the ascendency even
in the tropics, where their frail bodies have to compete with hosts of
plants which are physically much more vigorous.
Between the Yucca and the Yucca Moth exists a wonderful life-long
partnership for the purpose of furthering the reproductive processes of
both. Surely, Nature moves in mysterious ways.
Insects are the chief marriage priests of the plant world, but in the
tropics they are aided and abetted by Humming-Birds, Sun-Birds and
Lories, which are all provided with long, tubular tongues.
Most insects act as if they were unaware of the important place they
occupy in plant hymeneals. So intent are they on their honey-gathering
that they become covered from head to foot with pollen without
appearing to notice it. Yet in a few instances, the Bees not only
recognize that they have been pressed into the plant’s messenger
service, but by underhand methods seek the rewards of labour without
giving adequate return. They have learned how to cut a hole in the
calyx tube of the Bean and the Scarlet Runner, and get at the precious
honey by short cut. If all Bees and other fertilizing insects should
master this trick, the flowers would have to wear defensive armour or
perish.
Pollen to be effective must remain dry. The plants have perfected many
devices to shield it from moisture. Frequently, the flowers hang so
that their petals act as tiny umbrellas for it. Others wear rainy day
hoods, and practically all close when the night mists are abroad.
The necessity for dry pollen obtains even among the water plants. If
they are surface-floaters like the Pond Lily or the Victoria Regia, it
is easy enough for them to thrust their blossoms up into the air, where
they may be as dry as though they were on land. The sub-aqueous plants
have a harder problem and are sometimes driven to developing their
flowers in leaf air-chambers below the surface. The Water Chestnut
(_Trapa Natans_) makes itself buoyant at its flowering period with
generated air and rises en masse to the surface. After fertilization,
it sinks again to its sub-aqueous quiet.
Self-fertilization in its strictest sense occurs within the
individual flower. Plants only resort to it as an extreme measure
and commonly make use of many devices to prevent it. In the Iris,
the petal-like stamens are in direct contact with the pistil and yet
self-fertilization does not result, because the pollen surface is
always carefully turned away from the ovary.
By bringing their pistils and stamens to maturity at different times,
many flowers make sure that they will not fertilize themselves. Such is
the case in the Bulbous Buttercup and the Arrowhead.
Flowers of the same tree or bush might be called distant cousins. Their
union results in healthy offspring, though the marriage of still more
divergent individuals is preferable. Plants like the Begonia, which
bear single-sex flowers, often grow in somewhat isolated positions and
so must intermarry a great deal among themselves. Staminate flowers at
the top of a stalk can shower pollen over many female flowers growing
below them.
The exception always proves the rule, which explains why we find a
few flowers which deliberately choose to fertilize themselves. In
the Fuchsia, the flower droops, throwing the long pistil below the
stamens, which can readily drop pollen onto it. Minute hooks hold
the petals of the Indigo and Lucerne partly closed until the flower
is completely developed. When they give way, the petals fly back, so
shaking the whole flower that the anthers shower pollen on the pistil.
The single-sex flowers of the Aloe bend near each other at mating time.
The Violets and Polygalas are also largely self-fertilizing. They are,
therefore, borne under the leaves or close to the ground, where they
attract little attention.
The love and marriages in plantdom may seem to be largely instinctive
and mechanical, but that is probably because we have not investigated
them sufficiently. The Persian poet Osmai believed that the plants had
affairs of the heart as real as those recorded in the human world. Here
is his account of one:--
“I was possessor of a garden in which was a Palm Tree, which had every
year produced abundance of fruit; but two seasons having passed away
without its affording any, I sent for a person well acquainted with the
culture of Palm Trees, to discover for me the cause of the failure.
“‘An unhappy attachment,’ observed the man, after a moment’s
inspection, ‘is the sole cause why this Palm Tree produces no fruit.’
“He then climbed up the trunk, and looking around, discovered another
Palm at no great distance, which he recognized as the object of my
unhappy tree’s affection; and he advised me to procure some of the
powder from its blossoms and to scatter it over the branches. This I
did; and the consequence was my Date Palm, whom unrequited love had
kept barren, bore me an abundant harvest.”
[Illustration: FLORAL OFFERINGS IN A MOUNTAIN CATHEDRAL]