LESSON V.
THE GROWTH OF PLANTS.
How do plants grow? That is a very great question, but we will try to find a little part of the answer.
IN SUN AND DEW.
IN SUN AND DEW.
You know when you look at a flower, as a lily, you find in the middle of it some tall, slender parts which you are told are stamens and a pistil. The pistil usually stands right in the centre of the flower. It seems to be the most precious part, and all the other parts take care of it.
I knew a boy who told his sister that “they said at school that plants had little guns.” He thought the word pistil meant something to shoot with! But if there is any shooting done by plants, it is done by the stamens, and not by the pistil.
On the top of the stamen is a little box, to hold the pollen, or flower-dust. You read of that some time ago in the lesson about bees and ants, in your other Nature Readers.
When the pollen is of full size, or ripe, the little box bursts open, and out the pollen flies. The growth of the plant begins here, with the pollen.
A tiny grain of pollen, falling on the top of the pistil, begins to grow. It puts out little threads like roots. These grow down the stem, or post, of the pistil into the seed case. There they find the seed germs, and when the pollen comes to them, the germs begin to grow. They grow very fast.
It is then that the pretty flowers fade. The work of the blossom is done when the pollen is ripe, and the seed germs begin to grow.
But while the blossom dies, the seed bag grows larger and larger. As the seeds ripen, the bag, or case, that holds them becomes brittle. It will break easily. Often this pod, or seed bag, bursts open when the seeds are ripe. Then the seeds fly all around.
They fall upon the ground. There with the wind and rain and the slight change of the top soil, they slowly sink into the dirt. They keep moist and warm until spring. Then they sprout out as you see the beans do.
Some seeds will die if left to lie all winter in the ground. We say such seeds are not hardy. They are seeds that are not native to the place where they grow. Seeds are hardy in their native places.
Now you have seen how the seed germ grows to be a ripe seed. You have seen how the ripe seed sprouts into a plant. You know that plants grow. They increase in size. They put out more leaves. They have flowers and seeds. How is this done? It cannot all be explained, but a little of it can be.
Look at yourself. You grow. Suppose you did not eat? Would you grow? If you stop eating you will shrink up, and be thin, and even die. Have you never heard people say that if children do not have enough to eat, they will be small and not grow well?
You grow by eating. So does the plant. But mind you, when we speak of the plant as eating, we mean reallydrinking. The food the plant takes from the earth must come to it in a liquid form.
You know of some insects which take their food by sucking the juice out of things.[6]So the plants get their mineral food, held in water. They suck the water out of the ground, by the wee mouths at the tips of the root fibres.
You know, when it is very dry the plants droop. People say “it is so dry that the crops will not grow.” Even the leaves of the trees die and fall off in a very dry time. They die for lack of food-drink.
You have a stomach where the food that you get is so changed that it will make for you good blood. The blood feeds and builds up every part of your body. The plant has no stomach, but its leaves serve it for the same purpose.
In the leaves the plant food is turned into stuff like the plant. But how does the food pass into the leaves? See the tall tree! How does the plant food go from the roots to the top-most leaves? It runs up little pipes or cells.
Plant stems are made of bundles of these tiny pipes. Do you now fancy long slim pipes, as long as the stem or trunk of a tree? Dear me, no! These tubes are very short.
But the bundles of them are laid along, all up the stem. They are laid end to end. Or you may call it onelong tube, with little walls, or partitions across. How does the sap pass through these walls? It would be very hard to tell.
What we know is, that it does go through very quickly. Take a flower with a clear green stem. Put it into a glass of water in which is some red or blue color. You can watch the rise of the colored water by the change in the color of the stem.
Take, in your garden or flower-pot, a plant that is dry and drooping. Pour water on it. Soak the earth about it well. In a very little time you will see the plant revive. The leaves will look fresh. The flowers will hold up their drooping heads.
I have seen a plant quite changed in this way, in half an hour. So you see, in this little time the roots drank the water from the earth. The water, as sap, ran up all the pipes, through all the partition walls. The flower was fed in every part.
When the plant is young and tender, it takes in much of its food through the whole surface or skin. It drinks in air, rain, and dew, through its skin. But as the plant gets older, and harder, it feeds more and more by the new roots and young leaves. At last, it takes almost all its food by the root and new leaves. I shall soon tell you what leaves eat.
Why then does any plant or tree look so much betterfor a good washing? One reason is that the dust is washed off. Then the pores, or little holes in the skin, are free and open. The plant can breathe through all its skin.
Do not forget that. Your skin is also full of little pores. They need to be kept open by plenty of washing.
Let us go back to those little root-mouths. When they drink water, they get some solid stuff. Every drop of water has a mite of mineral in it. It is this solid matter that makes plant fibre. It is this that is left as ashes when you burn a plant, or bit of wood.
The juice of plants is calledsap. When the root drinks the water from the earth, it travels up through the pipes, through all the cell-wells. So it soon reaches the leaves. What do the leaves do with it?
The leaves, having a wide surface, spread out the sap to the light and air. The heat of the sun cooks the sap. That is, it sets free, in a sort of steam, the clear water. The solid parts of the sap are left.
You know that things are made thicker by cooking. Does not the molasses become thicker when you cook it for candy?
When the sap is made thicker it is like glue. But it is still very thin glue. Also the light and air and heat change the sap in other ways of which I cannot now tell you.
But the sap, being changed in the leaf, is now true plant stuff. It must travel through the plant to build it up.
It is only in the green parts of the plant that the sap is changed to true plant material. What was at first mineral, held in water and air, is now vegetable, or plant matter. Now you see why a plant must have air and light, or it will not grow.
Now that it is fit for plant food, the sap sets out to run through all the plant. It must go to every part to build all up.
There are not two sets of tubes, one for raw and one for cooked sap. All must run through the same cells. So you see, the sap will be mixed. The raw sap going up has some food sap in it. The food sap runs about with some raw sap mixed with it.
Yet, after all, each kind reaches the right place. All the raw sap is cooked, all the food sap builds the plant. Here it builds root, there leaf, there stem, there flower, or seed.
Did you ever notice how fast a plant will grow? Choose out some flower or weed. Watch it. Seehow the tiny stem becomes tall and stout. See how the little leaves grow large and thick. A sunflower is a fine plant to watch in this way.
FOOTNOTES:[6]Nature Reader, No. 1, pp. 29, 65.
[6]Nature Reader, No. 1, pp. 29, 65.
[6]Nature Reader, No. 1, pp. 29, 65.