WE AND THE PLANT PEOPLE.
We live and the plants live. Probably neither we nor the plants spend much time thinking about what we owe to each other.
The plants are excusable for this, for they are not great thinkers, at least so far as we know.
But we owe so much to them, we ought to stop and think about it once in a while. We are indebted to them not only for the food we eat, but for the air we breathe.
We know about chlorophyll and the starch it makes, and how this starch is stored up in potatoes and wheat and corn and rice and all sorts of food grains and vegetables.
We know, too, how the roots suck up substances from the earth which we need in our bodies, and how they are stored away with the starch or sometimes by themselves. We know, in short, how all the food we eat is made first or last by the plants. Not only do we owe our food to the plants, but all animals do.
You see, animal cells are not able to take carbon dioxide and water and ammonia and other gases and minerals and work them up into living cells.
The plants have to do this for them; and then the animals eat the plants, for animal cells are able to work starch and sugar and plant protoplasm over into animal protoplasm, which can build all sorts of animal cells. So all the animals in the world get their food from the plant world. If the plants were to stop living, all the animals in the world would soon starve to death. The word “animals,” you know, means every living thing that is not a plant; in this sense flies and bees and oysters and caterpillars are animals as well as dogs and cats and such large creatures. Last of all, we ourselves are animals.
So the animal world would be in a sad predicament if anything should happen to the plants.
But there is more to thank the plants for than food. That is a pretty large item certainly; but what do you think of having to thank them for the air we breathe as well? Yet this we shall have to do if we begin thanking them at all.
You know about oxygen, of course. It is one of the gases that make up the air; and I may as well remind you that air is composed principally of oxygen and nitrogen gases,—about four times as much nitrogen as oxygen, but the oxygen is the most important to us. We do not use the nitrogen in the air at all probably. It serves the purpose of diluting the oxygen, which would be too strong for us if it were not mixed with nitrogen. But what we do use is the oxygen.
That goes into our lungs, and some of it does not come out again. It passes into the lung cells and from them into the blood, and is carried by it all over our bodies to all the millions of cells.
We need a great deal of oxygen, and if the supply should be cut short we would die.
All animals need oxygen; even the worms in the ground and the fishes and oysters in the water must have it. So great quantities are being used up all the time.
Now, you know, when the plants pull carbon dioxide to pieces, they keep the carbon and return the oxygen to the air. In this way we get it to breathe.
But there is more than this to the matter in hand. We are all the time breathing out carbon dioxide as an impurity; so are all the millions upon millions of animals in the world.
The air might in time contain enough carbon dioxide to kill us if there were not some way of getting rid of it. You know what that way is.
The plants use it up. So by giving oxygen into the air and taking out carbon dioxide, the plants keep the air fit for us and all animals to breathe.
But there is more than this we have to thank them for.
They shade the earth and regulate the rainfall and the water supply.
Where forests grow there are always streams of water, and the large water courses are kept full the year round.
The Mississippi River depends upon the far-away forests for its broad stream.
The spreading crowns of the trees shade the earth and prevent the water which falls as rain or dew from evaporating rapidly. It collects into streams and flows through the land, keeping the earth fresh and beautiful.
More than this,—large forests cause the rain to fall and the dew to collect. Their leaves condense the moisture in the air and cause it to fall as rain or be deposited as dew.
When people recklessly cut down the forests in a country, the water courses dry up, and even the largest rivers are affected.
When the spring rains fall over a country whose trees have been cut away, the water rushes down the little streams all at once and causes a terrific flood in the large rivers. It soon drains away; then the rivers fall lower and lower until they nearly dry up. This state of affairs is a great calamity, because the people can no longer raise crops on the land near where the old forests stood, for it is parched and dry months at a time.
Moreover, boats laden with coal and grain and all sorts of things can no longer pass up and down the rivers, because the water is too low.
People ought to think of these things and not destroy too much forest land. After awhile we shall have to go to work and plant trees instead of cutting them down or burning them; but it takes a long time for trees to grow, and a wiser way would be for us to take care of those we have.
You have heard a great deal about plants eating and the good they do us by eating the carbon dioxide in the air. They take this in through their leaves, and you remember they take in all their other food materials—water, nitrogen compounds, sodium, potassium, magnesium, and many other substances—through their roots.
But they do more than eat; they also breathe.
They breathe everywhere over the surface of their bodies where there are stomata or where the skin is not too thick for the air to penetrate it.
And I must tell you they breathe just as we do,—that is, they take in air, use the oxygen, and give off the carbon dioxide.
It seems rather inconsistent of them to take in carbon dioxide as food and throw it off as a waste at the same time, but that does not trouble them; they do not care whether they are consistent or not. And it is true they take in carbon dioxide and give off oxygen, and take in oxygen (in the air) and give off carbon dioxide, in one breath as it were.
You see, it is different parts of protoplasm at work that does this; one part—that in the chlorophyll bodies—is attracting carbon dioxide, breaking it up, and casting out oxygen. Other protoplasm in the cells outside the chlorophyll bodies attracts and uses the oxygen, while the carbon dioxide comes to the stomata from different parts of the plant as a waste material, just as it comes to the cells of our lungs to be cast out.
So plants, by breathing, make the air a little impure, but they destroy or break up so much more carbon dioxide than they make that on the whole they act as powerful purifiers of the air.
When we think of the great forests of the tropics, all overgrown with luxuriant vegetation, we may remember that those tangles of vines and trees and strange growths are our friends no less than the grass and bushes in our dooryard.
For there is a carrier always at work bringing the pure air to us and carrying away the impure air which we create. This carrier is the air currents. The great winds sweep about the earth, bearing the oxygen from the forests to the crowded cities, and sweeping away the carbon dioxide from the cities to the fields and woods. The winds, too, stir up the water where the water plants and fishes live, and help keep it full of air for the things in it to breathe; the tides and currents help, so as far down in the water as there are living things, you may be sure there is air for them to breathe. There would not be air enough for you, because you need so much; but for them there is plenty.
Swirling around the earth go the winds, carrying the oxygen to the people and the carbon dioxide to the plants, for the plants are as glad to get the carbon dioxide we breathe out as we are to get the oxygen they give off.
And we are glad, when we come to think about it, that we are able to give them something in return for all they give to us.
You see, we need each other,—plants and people, and the winds are friends to us both.
