VII
THE FERTILIZATION OF THE FLOWER
As a preparation for this work, let the children notice the flower-dust or pollen that shakes out of the flowers or is seen clinging to the anthers.
[Ill.u.s.tration: BEE--SHOWING POLLEN-BASKET]
The child presently discovers where the pollen comes from. It is hidden in the anthers. He can hunt in all the flowers to find these little pollen-boxes, some of which, as in the goldenrods, are so small that he will have hard work to find them, even though they shed such clouds of pollen. He can notice the different kinds of stamens, see how some have long stems or filaments, others short ones, others again none at all.
The filament is of no other use than to hold up the anther. The anther with its pollen is the important thing; so there may be useful stamens with no filaments, but never useful stamens with no anthers.
The amount of pollen in the flowers is always astonishing and interesting. Why should there be so much?
That the bee gathers honey from the blossoms is one of the earliest things the child learns. Just whereabouts in the flower-cup, and just how the bee finds this honey, how it carries it home, where and how and why it stores it in the hive, is one of the most fascinating of stories, as good as a fairy tale. In connection with this comes very naturally the story of the bees and the pollen. The child will be delighted to learn that the bees collect pollen as well as honey; that the honey bees and b.u.mble-bees have baskets on their legs on purpose to carry it home; that they knead it up with honey and make it into what is known as bee-bread.
We seldom see bee-bread these days, as patent hives furnish all the honey found in city stores and no bee-bread is sold. In remote country places, however, where the honey is removed _en ma.s.se_ from the hive, there will be plenty of bee-bread to give piquancy to the children"s bread and honey. Moreover, where bees are kept, the bee-keeper can usually be persuaded to take out a little bee-bread for the children to see and taste; for it is always present no matter what the kind of hive used, though it is not always easily obtainable, for where their household arrangements permit, the bees generally prefer to store it in the lower chambers away from the honey. Thus the flower supplies large quant.i.ties of food for the bees and for us, and long ago, before America was discovered and before cane-sugar came into use, the people depended upon honey for their sweetening.
When the children have found how general is the presence of pollen in the flowers, where it comes from, and how it is gathered by the bees, they can learn that the pollen is valuable to the plant itself. It is indeed one of the most necessary parts of the flower, for without it the ovules could not develop.
The effect of the pollen upon the seeds can be prettily ill.u.s.trated by a simple experiment. Take two or three little pots of geraniums whose buds are just ready to open. Be sure to have single geraniums, and to stand them where they will not be disturbed and where the wind will not blow upon them. Shortly after the flower opens, the anthers will be seen crowded in its throat and covered with pollen. After a few days the pollen will have dried up, and the style, tipped with a five-rayed star-like stigma, will push up above the anthers. Mark pot No. 1 as untouched. From pot No. 2 carefully take a little pollen on the end of a small clean paint-brush or tooth-pick and touch with it the five-rayed, star-like stigma of the flowers in pot No. 3. Be careful not to let any of it touch the stigmas of the flowers in pot No. 2, the pot from whose flowers the pollen is taken.
Leave the flower-pots undisturbed and watch results. When the flowers finally drop their petals, in pots No. 1 and No. 2 there will be no seed-pods remaining, everything will drop, including the little flower-stalks and the main stalk supporting the whole cl.u.s.ter of flowers. In short, no trace of flowers will be left. So far as seed-forming is concerned, the flowers might as well never have blossomed. Very different will be the result in the flowers of pot No.
3. These received the pollen on the stigma, and in some way this pollen affected the ovules so that they began to develop. We say the flower was fertilized by the pollen, and "fertilized" is a valuable word to learn at once. When the petals of the fertilized flowers fall, all does not fall. There remains the ovary with the long style and the star-like stigma. The ovary continues to grow, as do the seeds within it. Since the geranium is a house-plant, raised under unnatural conditions, not all the fertilized flowers will succeed. Some may fall at once, like the unfertilized ones. But out of the whole bunch of fertilized flowers some will be almost sure to start the development enough to show that in some way the fertilized flowers were able to produce seeds, while the others will in no case make any attempt at seed-forming. Even though none of the seeds come to perfection, the fact that they start at all will demonstrate the effect of the pollen. The geranium is a good plant to use in ill.u.s.trating this point, because it is so constructed that it cannot fertilize its own flowers.
What the child thus far learns is simply that the pollen is in some way necessary to the development of the ovule. If the experiment with the geraniums is not practicable, the child can be told that the pollen is necessary to the development of the seed, that it falls upon the stigma and nourishes the little ovules down in the ovary, and that no seed can form without the aid of the pollen. All the seeds we plant in the flower gardens or in the vegetable gardens, and all the grain we sow in the fields, are produced by the help of pollen. All the peas and beans and other seeds we eat owe their existence in part to the pollen, and without it they could not develop.
Some parents teach their children at once that the pistil is the mother-part of the plant, caring for the young seeds, the stamens the father part, providing for them, and that the stamens and pistil growing in the same flower are brothers and sisters. Other parents prefer to use only botanical terms, leaving the extension of the thought to later consideration or to the child"s own logic, for children often reason out all the facts--in a very general way, of course--from only this botanical study.
But we are not yet done with the pollen. It not only a.s.sists the ovule to develop, but it impresses upon it its own characteristics. In other words, the seed inherits from the pollen as well as from the ovule.
Inheritance is a very wonderful thing. It is that power which causes the offspring to resemble its parents. In some wonderful way the tiny ovule, the tiny pollen grain, remember everything about the plant they came from and are able to transmit this memory to the developing offspring, so that it may become like its parents.
Again, the child under eight can understand the princ.i.p.al facts of fertilization. The older child can add to his stock of facts, and one of the things he will be likely to want to know is how the little pollen grain up on the stigma can influence the ovule down in the ovary.
We know how the ovule is formed. We know that it grows from the inside of the ovary. If we were able to examine the development of the pollen grain inside the anther from its very beginning, we should find the same thing true of it. The anther is a little box like the ovary, and the pollen grain grows from the inside of it, being at first a part of it and nourished by the same sap. When it became ripe it fell free into the anther cavity. We then have a little box full of ripe pollen grains.[1]
The pollen grain is like the ovule in structure, only much smaller. It is so tiny and the anther so small that we cannot watch its development as we can that of the ovule. But botanists have taken great pains to examine the pollen and to watch its development under the microscope, so that from them we know the truth.
If we examine the young ovule we find it apparently nothing but a little sac full of a semi-liquid substance. This semi-liquid substance, or at least a part of it, is alive and is very important. It is protoplasm, which is the only living substance; all the living parts of plants and animals are made from protoplasm.
[Ill.u.s.tration: POLLEN GRAINS (MAGNIFIED), AND STIGMA]
The pollen grain is also a little sac containing protoplasm. Thus we have these two little sacs of living substance, each growing in a similar manner, one to the inside of an ovary, the other to the inside of an anther. Naturally, it is the living substance in these little sacs that is important. It is the living substance of the ovule that unites with the living substance of the pollen grain to become a seed; or, to say the same thing another way, it is the living substance of the pollen grain that unites with that of the ovule to become a seed; or yet again, it is the union of these two living substances that enables the seed to develop.
[Ill.u.s.tration: THE POLLEN TUBE Pa.s.sING THROUGH THE STYLE TO THE OVARY]
To understand how the pollen substance finds its way to the ovule substance let us examine the pollen grain a little more carefully.
Pollen grains are of many shapes, though usually they are globe-shaped, or football-shaped. Tiny as they are, the outer skin is often marked with grooves and ridges in a very ornamental manner. They have two skins, an outer hard one, a softer inner one. The outer skin is not equally thick and hard all over. It has little glazed spots sometimes, like little glazed windows. Now, when the pistil is ripe the stigma is _sticky_. When the pollen grain falls upon this sticky stigma its inside wall swells up, just as the bean does when we soak it. But the outside wall cannot swell, consequently the inner wall finally breaks through at one of the weak spots in the outer wall. Then the inner wall absorbing moisture and nutriment from the stigma actually grows, becoming a tube, which finds its way down through the style. The living substance of the pollen grain runs into the tip of this tube, and so is carried with it down through the style. The tube is nourished by the juices of the style as it goes along, and finally it gets to the ovary and the ovule. Every ovule has a tiny opening, or micropyle as it is called, and it is now easy to guess what that is for. The pollen tube pushes straight toward the micropyle, enters into the ovule through the micropyle, and then the living substance it has carried all this distance in its tip breaks through its delicate wall and mingles with the living substance of the ovule. When this has happened, the ovule begins to grow and to develop into a seed.
[Ill.u.s.tration: ENTRANCE OF POLLEN-TUBE THROUGH THE MICROPYLE TO THE OVULE]
We see that the whole pollen grain could not possibly force its way down to the ovule. It cannot move of itself, for one thing, and if it could it is too large to pa.s.s between the tissues of the style. So it simply sends down the long tube, which grows fast, pushing along through the style, whose tissues are rather loose, and carrying with it the only valuable part of the pollen grain, its living protoplasm. No ovule can possibly grow into a grain without this tiny bit of pollen.
In explaining this union of the two protoplasms, the child"s mind can be turned upon the wonderful mystery--one of the great mysteries of the universe--of how this tiny atom can influence the whole future plant.
There is ample opportunity here to elevate his mind and spirit to a high plane, and, by talking of the wonders of inheritance, to give many a hint for future reflection. Without this law of inheritance the world would be chaos. Imagine the seed of a rose sometimes developing into an oak tree, the egg of a bird into a bee or a trout. Imagine eggs developing haphazard into anything. There would be no use in living.
Nothing could be depended upon. But there is no danger that any such thing will happen: the law of inheritance is unyielding. From a rose seed must come a rose bush,--and this is good. But on the other hand, from the seed of a weak, poor plant will grow another weak, poor plant.
Whatever the parent is, good or bad, that must the offspring be. But sometimes the offspring inherits only the best in the parents, and so is better than they.
Thus in gathering his seeds, the child will select only the largest and best and take them from only the best plants to put in his garden the next year, at the same time planting beautiful truths in the garden of his soul. Not the least of these truths is a profound sense of the immutability of law. Through his nature-work the child can learn as nowhere else the stern, unbreakable decrees of law, and the respect and reverence due to it from every intelligent being. Another important and far-reaching fact that the child can learn from his garden is, that his plants are good or poor according to the care he takes of them. They must have the right kind of food (soil), the right amount of water, the right temperature and surroundings,--some loving the open sunshine, others needing to be partly protected from it. In short, according as its environment is suited to its needs, and as its inheritance is good or bad, will the plant be strong and handsome or otherwise.
Another truth to be learned from the flowers is the value of cross-fertilization. This was demonstrated by the great Darwin, who fertilized a number of flowers with their own pollen, and an equal number with the pollen from the blossoms of another plant of the same kind. When the seeds were ripe he gathered them, carefully keeping those of the self-fertilized flowers separate from the others. The next season he planted both sets of seeds under exactly the same conditions, that is, they had the same soil and moisture, the same sun and air, and the same care. The plants that grew from these two sets of seeds were very different, those from the self-fertilized seeds being smaller and weaker in every way than those from the seeds fertilized with pollen from another plant, or cross-fertilized, as we say, thus proving that it is not best for the plant to be self-fertilized. Someway, it needs the stimulus from less closely related pollen in order to grow vigorously and perfectly.
While the cross-fertilization of the same order of plants is so desirable, it is not possible for the pollen of one order to fertilize the ovules of another order. There must be a certain degree of similarity between flowers able to fertilize each other. The pollen of an apple blossom might, for instance, rest upon the stigma of a lily, but the pollen could not penetrate to the lily ovule. It would have no effect upon the lily.
That the seed inherits equally from the ovule and the pollen grain is a truth that should be impressed in many ways. It is very wonderful that anything so small as a pollen grain, often as small as the tiniest speck of dust, should be able to transmit to the young seed the peculiarities of the plant from which it came. That it does this, the child himself can prove in a most interesting way. He can plant some white petunia seeds in one side of his garden, and some red ones in the other. The seeds should come from a reliable florist"s in order to be sure of results. When the petunias ripen their seeds, those from the white flowers should be gathered and carefully labelled, and then those of the red flowers, care being taken not to mix the two colors. The next summer, plant the seeds as before. When the flowers blossom, those in the white bed will no longer be white,--some may be, but others will be red, and still others red and white. The same will be true of the flowers in the red bed. What has happened? The bees going from flower to flower have carried the pollen from one bed to the other, and some of it, rubbing off on the stigmas as the bees searched for honey, fertilized the flowers. Thus some of the ovules of the white flowers received an impression of red from the pollen of the red flowers, and grew into red flowering plants. In others where the impression of red was less strong, the result was the production of red-and-white spotted flowers.
By fertilizing white flowers with pollen from red ones we can almost always get seeds that will develop into plants bearing flowers that are not white. What is true of color is true of other characteristics of the plant, such, for instance, as size and shape of leaves, habit of growth, size, shape, and quality of fruit, etc. Thus by careful cross-fertilization, we are able to produce not only beautiful and new blossoms, but also many delicious new fruits. Most of our cultivated fruits have been produced in this way. For instance, if two species of wild strawberries were found, one, large and beautiful but sour or tasteless, the other, small but delicious, the two could be bred together until finally a perfect berry, large and well-flavored, would result.
[Ill.u.s.tration: FLOWERS NEEDING CROSS-FERTILIZATION, SOME WITH OVARY BUT NO STAMENS, OTHERS WITH STAMENS BUT NO OVARY]
When the children are interested in their gardens they can try to make a new flower, using for the first experiments one that comes up from the seed, blossoms, and matures its seeds the same year, and also readily changes its color as a result of cross-fertilization. Such are the petunia and the sweet-pea. The prettiest new flower produced can be marked and its seeds saved for future use, and the flower can have a name of its own. Florists often name their choice new flowers from some beautiful woman, and it would be a pretty tribute on the part of the child to name his favorite new petunia or sweet-pea after his mother. Of course this work will necessarily be very crude and the results uncertain, since the successful production of new plants is a science in itself; but enough can be done to interest the young experimenter thoroughly and enable him to learn many valuable lessons. In these early, childish experiments, an interest in gardening may be awakened, which will last through life, the man, the woman, finding rest, relaxation, exercise, and pleasure in going from the trying daily work to the garden a while every day. Even a plot of ground a few feet square can afford great opportunity for experiment and beauty.
Cross-fertilization among the plants does not, of course, depend upon man as an agent. Since cross-fertilization is so valuable, it is not surprising to find many devices in the plant world for securing it.
Honey and color, which attract winged messengers, are among the most universal helps to cross-fertilization. In many cases, the structure of the flower is such that it cannot fertilize itself. In the geranium, the stamen and the pistil in the same flower mature at different times. In some species, as among the lilies, the style is so long that the pollen could not fall upon it without artificial aid. Some flowers are so constructed that they can be fertilized by certain kinds of insects and by no others; among these are the orchids and our clovers and milk-weeds. Again, some flowers have an ovary but no stamens, while a neighbor has stamens but no ovary, making self-fertilization absolutely impossible.
Indeed there is nothing more fascinating in the study of botany than the methods by which the flowers secure cross-fertilization, nearly all of our common garden-flowers affording ill.u.s.trations. Here too, is a field where the young botanist can do really valuable work, for while much is known and has been written on the subject, much remains unknown. There are many books that give valuable and delightful information about cross-fertilization.
The method of fertilization of the flowers satisfactorily accounts for the great amount of pollen produced. Being blown by the wind or carried by insects, much of it is wasted, consequently there must be ample allowance made for this waste. So the flowers produce thousands of pollen grains which they can never use themselves.
VIII
WHAT CAN BE LEARNED FROM THE LIFE OF THE FISH
Whatever is universal is good.
Whatever is universal is true.
Whatever is universal is beautiful.
Nothing disperses, so to speak, the fogs enveloping the thought of s.e.x like the realization of its universality. The air clears when we know that every living thing is bound by the same laws, even the flowers in our gardens.
We have an interesting testimony as to the helpfulness of this thought from one of the great educators of youth, Frobel. Speaking of his own childhood when he became conscious of what his father, who was a minister, was constantly meeting in his parish work, he says: