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- The Fairy-Land of Science - 20/30 -
round him. Then dream for a little while about sound, what it is, how marvellously it works outside in the world, and inside in your ear and brain; and then, when you go back to work again, you will hardly deny that it is well worth while to listen sometimes to the voices of nature and ponder how it is that we hear them.
LECTURE VII THE LIFE OF A PRIMROSE
When the dreary days of winter and the early damp days of spring are passing away, and the warm bright sunshine has begun to pour down upon the grassy paths of the wood, who does not love to go out and bring home posies of violets, and bluebells, and primroses? We wander from one plant to another picking a flower here and a bud there, as they nestle among the green leaves, and we make our rooms sweet and gay with the tender and lovely blossoms. But tell me, did you ever stop to think, as you added flower after flower to your nosegay, how the plants which bear them have been building up their green leaves and their fragile buds during the last few weeks? If you had visited the same spot a month before, a few (of) last year's leaves, withered and dead, would have been all that you would have found. And now the whole wood is carpeted with delicate green leaves, with nodding bluebells, and pale-yellow primroses, as if a fairy had touched the ground and covered it with fresh young life. And our fairies have been at work here; the fairy "Life," of whom we know so little, though we love her so well and rejoice in the beautiful forms she can produce; the fairy sunbeams with their invisible influence kissing the tiny shoots and warming them into vigour and activity; the gentle rain-drops, the balmy air, all these have been working, while you or I passed heedlessly by; and now we come and gather the flowers they have made, and too often forget to wonder how these lovely forms have sprung up around us.
Our work during the next hour will be to consider this question. You were asked last week to bring with you to-day a primrose- flower, or a whole plant if possible, in order the better to follow out with me the "Life of a Primrose." (To enjoy this lecture, the reader ought to have, if possible, a primrose- flower, an almond soaked for a few minutes in hot water, and a piece of orange.) This is a very different kind of subject from those of our former lectures. There we took world- wide histories; we travelled up to the sun, or round the earth, or into the air; now I only ask you to fix your attention on one little plant, and inquire into its history.
There is a beautiful little poem by Tennyson, which says -
"Flower in the crannied wall, I pluck you out of the crannies; Hold you here, root and all, in my hand, Little flower; but if I could understand What you are, root and all, and all in all, I should know what God and man is."
We cannot learn all about this little flower, but we can learn enough to understand that it has a real separate life of its own, well worth knowing. For a plant is born, breathes, sleeps, feeds, and digests just as truly as an animal does, though in a different way. It works hard both for itself to get its food, and for others in making the air pure and fit for animals to breathe. It often lays by provision for the winter. It sends young plants out, as parents send their children, to fight for themselves in the world; and then, after living sometimes to a good old age, it dies, and leaves its place to others.
We will try to follow out something of this life to-day; and first, we will begin with the seed.
I have here a packet of primrose-seeds, but they are so small that we cannot examine them; so I have also had given to each one of you an almond-kernel, which is the seed of the almond- tree, and which has been soaked, so that it splits in half easily. From this we can learn about seeds in general, and then apply it to the primrose.
If you peel the two skins off your almond-seed (the thick, brown, outside skin, and the thin, transparent one under it), the two halves of the almond will slip apart quite easily. One of these halves will have a small dent at the pointed end, while in the other half you will see a little lump, which fitted into the dent when the two halves were joined. This little lump (a b, Fig. 37) is a young plant, and the two halves of the almond are the seed leaves which hold the plantlet, and feed it till it can feed itself. The rounded end of the plantlet (b) sticking out of the almond, is the beginning of the root, while the other end (a) will in time become the stem. If you look carefully, you will see two little points at this end, which are the tips of future leaves. Only think how minute this plantlet must be in a primrose, where the whole seed is scarcely larger than a grain of sand! Yet in this tiny plantlet lies hid the life of the future plant.
When a seed falls into the ground, so long as the earth is cold and dry, it lies like a person in a trance, as if it were dead; but as soon as the warm, damp spring comes, and the busy little sun-waves pierce down into the earth, they wake up the plantlet and make it bestir itself. They agitate to and fro the particles of matter in this tiny body, and cause them to seek out for other particles to seize and join to themselves.
But these new particles cannot come in at the roots, for the seed has none; nor through the leaves, for they have not yet grown up; and so the plantlet begins by helping itself to the store of food laid up in the thick seed-leaves in which it is buried. Here it finds starch, oils, sugar, and substances called albuminoids, -- the sticky matter which you notice in wheat-grains when you chew them is one of the albuminoids. This food is all ready for the plantlet to use, and it sucks it in, and works itself into a young plant with tiny roots at one end, and a growing shoot, with leaves, at the other.
But how does it grow? What makes it become larger? To answer this you must look at the second thing I asked you to bring - a piece of orange. If you take the skin off a piece of orange, you will see inside a number of long-shaped transparent bags, full of juice. These we call cells, and the flesh of all plants and animals is made up of cells like these, only of various shapes. In the pith of elder they are round, large, and easily seen (a, Fig. 39); in the stalks of plants they are long, and lap over each other (b, Fig. 39), so as to give the stalk strength to stand upright. Sometimes many cells growing one on the top of the other break into one tube and make vessels. But whether large or small, they are all bags growing one against the other.
In the orange-pulp these cells contain only sweet juice, but in other parts of the orange-tree or any other plant they contain a sticky substance with little grains in it. This substance is called "protoplasm," or the first form of life, for it is alive and active, and under a microscope you may see in a living plant streams of the little grains moving about in the cells.
Now we are prepared to explain how our plant grows. Imagine the tiny primrose plantlet to be made up of cells filled with active living protoplasm, which drinks in starch and other food from the seed-leaves. In this way each cell will grow too full for its skin, and then the protoplasm divides into two parts and builds up a wall between them, and so one cell becomes two. Each of these two cells again breaks up into two more, and so the plant grows larger and larger, till by the time it has used up all the food in the seed-leaves, it has sent roots covered with fine hairs downwards into the earth, and a shoot with beginnings of leaves up into the air.
Sometimes the seed-leaves themselves come above the ground, as in the mustard-plant, and sometimes they are left empty behind, while the plantlet shoots through them.
And now the plant can no longer afford to be idle and live on prepared food. It must work for itself. Until now it has been taking in the same kind of food that you and I do; for we too find many seeds very pleasant to eat and useful to nourish us. But now this store is exhausted. Upon what then is the plant to live? It is cleverer than we are in this, for while we cannot live unless we have food which has once been alive, plants can feed upon gases and water and mineral matter only. Think over the substances you can eat or drink, and you will find they are nearly all made of things which have been alive: meat, vegetables, bread, beer, wine, milk; all these are made from living matter, and though you do take in such things as water and salt, and even iron and phosphorus, these would be quite useless if you did not eat and drink prepared food which your body can work into living matter.
But the plant as soon as it has roots and leaves begins to make living matter out of matter that has never been alive. Through all the little hairs of its roots it sucks in water, and in this water are dissolved more or less of the salts of ammonia, phosphorus, sulphur, iron, lime, magnesia, and even silica, or flint. In all kinds of earth there is some iron, and we shall see presently that this is very important to the plant.
Suppose, then, that our primrose has begun to drink in water at its roots. How is it to get this water up into the stem and leaves, seeing that the whole plant is made of closed bags or cells? It does it in a very curious way, which you can prove for yourselves. Whenever two fluids, one thicker than the other, such as treacle and water for example, are only separated by a skin or any porous substance, they will always mix, the thinner one oozing through the skin into the thicker one. If you tie a piece of bladder over a glass tube, fill the tube half-full of treacle, and then let the covered end rest in a bottle of water, in a few hours the water will get in to the treacle and the mixture will rise up in the tube till it flows over the top. Now, the saps and juices of plants are thicker than water, so, directly the water enters the cells at the root it oozes up into the cells above, and mixes with the sap. Then the matter in those cells becomes thinner than in the cells above, so it too oozes up, and in this way cell by cell the water is pumped up into the leaves.
When it gets there it finds our old friends the sun-beams hard at work. If you have ever tried to grow a plant in a cellar, you will know that in the dark its leaves remain white and sickly. It is only in the sunlight that a beautiful delicate green tint is given to them, and you will remember from Lecture II. that
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