CHAPTER VI
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.”
FLORAL OFFERINGS IN A MOUNTAIN CATHEDRAL
