CHAPTER X.

HOW PLANTS GROW.

MUCH of the following is taken from a pamphlet by W. S. Powell, of Baltimore, Md., and will no doubt be read with interest.

The Air. The air we breathe is a compound of gases. We cannot see the air, but we can feel it when we move our hand swiftly about, and we can observe its power when it is in motion and is called wind.

The air is a fluid which surrounds us on every hand, and it has a very important part in the growth of crops and the life of all plants and animals. Air is found to be made up of the union of two invisible gases, called oxygen and nitrogen. It has also, at times, other things mixed with it, but not a part of it, such as water, in an invisible vapor, and other gases. Without air no animal or plant can live. Growing plants take from the air poisonous gases which animals throw off from their bodies, and give back to the air what animals need for their good. So we see that the air is the means of keeping both animal and vegetable life on the earth. Animals in breathing the air use up the oxygen gas, and throw off a poisonous gas, called carbonic acid, while plants take up this carbonic acid, which is carbon and oxygen, use the carbon and reject the oxygen.

Water. Water is composed of two gases, oxygen and hydrogen, in the proportion of one part of the former to two of the latter; it composes four-fifths of the flesh and blood of man, and he uses three-fourths of a ton of it annually. Rain, which is an essential of all crops and of all vegetables, is produced by the evaporation of water in whatever form it may exist, from the land, animals, and plants; in this form it constitutes an invisible vapor that is taken up by the atoms in the atmosphere. The property of all air is to rise when heated; hence, whenever air at any place becomes heated by decomposition of any substances, whether in the soil or on its surface, or from the heat

of the sun, it ascends; as it ascends and meets with cooler currents, the invisible particles contained in it will condense into larger particles; after they become larger particles and saturated, the force of the ascending currents fails to support them, and they fall in the form of rain.

The air, however, has in it more or less of other gases, or other invisible constituents; strange to say, all the other elements or substances do not have the same affinity for each other, and will not unite or enter combinations. Copper and iron cannot be welded together, unless a solder is used that possesses an affinity for both. Water, however, has a great love for other substances, or they for it; among these substances may be mentioned ammonia and carbonic acid, which promote the growth and enter into the composition of all plants. A careful observation and analysis of the rain, both in this country and in Europe, shows that these substances are brought down in very considerable quantities by it. In France, about eight gallons of carbonic acid are brought down each year, per acre, and ammonia in varying amounts. In Kansas, where this subject has received attention, it appears that three and one-half pounds was the average amount of nitrogen brought down per acre, when the rainfall averaged 29 inches. If we suppose an average dressing of saltpetre, to about 200 pounds per acre, then this rainfall is about equivalent to one-ninth of this amount. As we go south, the amount of nitrogen in the rain increases, as is also proven in Kansas, at Manhattan, where the amount of nitrogen brought down by the rain was only about one pound, whereas 20° south of that point it was found to be over six pounds; in Maryland, the annual rainfall is about 42 inches, therefore we can safely calculate that about five pounds per acre of ammonia are conveyed to the soil through the rains.

The Soil. We have seen that air and water are each composed of two gases, chemically combined. The soil, or earth, is

a much more complicated substance, and varies greatly in its nature in different situations. While air is a fluid, and water a liquid, the earth is a solid. That is, it is solid in a cold state, for all solid things can be made liquid if they are subjected to

a sufficiently high degree of heat. All the metals can be made

to flow like water, if made hot enough, and the dry sand, mixed with other things, and heated to a high degree, flows off as glass, and gets still harder in cooling. The soils which cover the hard, rocky framework of the earth have been formed in many ways. The hard rocks have been ground up by ice, frost, and snow, dissolved by water, and carried by it from place to place, until nearly the whole earth is covered with this softer covering, in which plants and trees can grow. The decay of these trees added other substances, which did not before exist in the soil, and thus a larger growth was made, the decay of which still further added to the soil. It is this soil, made up of this mixture of mineral substances from the rocks, and vegetable decay drawn from the air, which we have to do with in farming. The soil, then, is a great mixture of many substances, and is very different in one locality from that which is found in another.

Plants. The many kinds of plants which the farmer grows for the purpose of harvesting from them his crops, are the most important things connected with his work. Let us see, then, what we can learn of the ways in which plants get their food, make their growth, and mature their seeds.

Plants, like animals, are living beings. We do not know exactly what this thing we call life is, but we can easily tell a dead animal or a dead plant; that is, we know when life is there and when it is gone. If we take a powerful microscope, we will find that the water of our ponds and ditches is full of living things, which we cannot see with our naked eye. Many of these we can see are animals, and many others we can see plainly are plants. And then we find some that we cannot be positive as to whether they are animals or plants. But we see that they are living and growing, and we find, in these very minute forms, some which are so small that 150 of them, placed end to end, would only make a line the thickness of the paper this is printed on. We find, then, that there is, in these small things, all of which have life, no distinct line between animal life and vegetable life. We conclude, then, that life in plants and life in animals is the same thing, only it shows itself in different ways, as the plants and animals get larger and better developed. The great oak tree of the forest has life just as our bodies have, but it manifests itself in a different way. The plant, then, is a living

thing, taking food, digesting it, and making growth. It is destitute of the power of moving about like animals, and in many ways a fully developed plant is very unlike a fully developed animal. But this vegetable life is the means by which animals are enabled to get food from the soil, for the plants can use matters in the soil and air to live and grow upon, which animals cannot get until the plants have made them into a shape they can eat. We see, then, that, without this plant life, there could be no animal life upon the earth.

It is very important, then, to understand just how plants get their food, what they eat, how they digest their food, and how they build up their structure, and mature the crops we use for food.

Where Plants get Food. We all know our common Indian corn, and what a great lot of food for man and beast it furnishes. Take a large plant of corn, fully mature; chop it up into a compact shape and weigh it. Then put it into an oven and get it thoroughly dry, as a chemist would in his drying-oven. When completely dry, weigh it again, and we find how much water it contained, and you will be surprised to find how much water this ripe corn had in it, though it will be hard for you to drive it all out, as a chemist would. Now take the dried corn plant and burn it slowly, so that no part of the ashes can be blown away. Then gather the ashes and put them into a crucible, and heat it until all the black particles are consumed, and nothing remains but white ashes. We will then find that these white ashes weigh very little, when compared with the weight of the good stalk and its heavy ear that we began with.

What has gone with all the rest, now that we have but a handful of ashes? The fire has destroyed it, you say. No, we cannot destroy anything. The burning only changed the form of the plant. The things which made up the greater part of the corn still exist, but they have gone back where the plant got them from, into the air. The little pile of ashes we hold in our hand, and which did not burn, is all that the plant got from the soil; the rest, and much the larger part, came from the air, in the shape of a gas, and has now gone back to the air. We see, then, that about nine-tenths of all our plants come from the air. All the food which plants get from the soil is left in the ashes,

and it got into the plant by being dissolved in the soil, by the water we dried off.

How Plants get Food from the Air. Take a large seed, like a Lima bean; press it, eye downwards, into a box of moist soil, in a sunny window, and watch it sprout and grow. You will notice that this bean is in two parts, inside of an outer skin. In a short time it swells, a little stem starts from the eye, and makes little roots in the soil. Then the two thick halves burst the skin and rise on the stem, and gradually spread out into two broad leaves. They are thinner now than when they merely formed the two parts of the bean, for they have given part of their material to form the little stem and roots, before they turned green. This turning green is a very important matter.

Suppose, instead of planting one bean in a sunny window, we had simply stuck it in moist sand in a warm place, and covered it over so that no light could reach it. It will swell and germinate, but the two halves will not turn green. Now take it and dry it, and you will find that it has not gotten any heavier, though apparently larger than when put in the moist, warm place; but take the bean which has been in the sunlight, and dry it, and you will find that it has already increased in weight. The bean in the dark did not grow, but only changed some of the food stored up in its thick halves into a little stem of rootlets. The one in the sunlight added something else. Now let us see how this was done. We have seen that, when the halves of the bean spread out into broad leaves, they became green. This green is caused by a substance formed in the leaves of plants which are in sunlight, and not in those that are kept in the dark. This substance is called leaf-green. It is found in little boxes in the leaf, which are called cells. These cells are placed side by side, somewhat like a honeycomb, and are so small that we cannot see them without a microscope, but between them there are little vacant places, still smaller than the cells. Opening into these spaces there are little holes in the leaf, particularly on the under side, which open and shut like little mouths with a pair of lips. These are really the mouths of the leaves, and through them the plant takes in all the food it gets from the air, and through them it also puts out some things it does not want, especially what water it does not need. These little mouths are so small