[Ill.u.s.tration: FIG. 9.

Soy-bean roots showing location, extent and depth of root-growth.]

Let us visit a field where some farmer is working a crop with a plow, or get him to do it, for the sake of the lesson. We will ask him to stop the plow somewhere opposite a plant, then we will dig a hole a little to one side of the plow and wash away the soil from over the plow (see Fig. 10), and see where the roots are. We will find that the plow-point runs under many strong-feeding lateral roots and tears them off, thus checking the feeding power of the plant, and consequently checking its growth. Now, if we can get a cultivator, we will have that run along the row and then wash away the loosened soil. It will be found that few, if any, of the main lateral roots have been injured.

Is it of any value to the farmer to know that roots extend laterally three to six feet and more on all sides of the plant, and that every part of the upper soil is filled with their branches and rootlets?

This fact has a bearing on the application of manures and fertilizers.

It tells the farmer that when he applies the manure and fertilizers to the soil he should mix the most of them thoroughly all through the soil, placing only a little directly in the row to start the young plant.

To find out how quickly the roots reach out into the soil, wash the soil away from some seedlings that have been growing only a few days, say, seven, ten and fifteen. (See Fig. 11.)

From our observations, then, we have learned the important lessons of deep, thorough plowing, careful shallow after-cultivation, and that fertilizers should be well mixed with the soil.

We are now ready to go back to our study of the habit of growth of roots, and can perhaps tell something of how the root does its work for the plant.

It is very easy to see how the roots hold the plant firmly in place, for they penetrate so thoroughly every part of the soil, and to such distances, that they hold with a grip that makes it impossible to remove the plant from the soil without tearing it free from the roots.

It is also on account of this very thorough reaching out through the soil that the roots are able to supply the plant with sufficient moisture and food.

We have doubtless observed that most of these roots are very slender and many very delicate. How did they manage to reach out into the soil so far from the plant? Or where does the root grow in length? To answer this question I will ask you to perform the following experiment:

=Experiment.=--Place some kernels of corn or other large seeds on a plate between the folds of a piece of wet cloth. Cover with a pane of gla.s.s or another plate. Keep the cloth moist till the seeds sprout and the young plants have roots two or three inches long. Now have at hand a plate, two pieces of gla.s.s, 4 by 6 inches, a piece of white cloth about 4 by 8 inches, a spool of dark thread, and two burnt matches, or small slivers of wood. A shallow tin pan may be used in place of the plate. Lay one pane of gla.s.s on the plate, letting one end rest in the bottom of the plate and the other on the opposite edge of the plate.

At one end of the piece of cloth cut two slits on opposite sides about an inch down from the end and reaching nearly to the middle. Wet the cloth and spread it on the gla.s.s. Take one of the sprouted seeds, lay it on the cloth, tie pieces of thread around the main root at intervals of one-quarter inch from tip to seed. Tie carefully, so that the root will not be injured. Place the second pane of gla.s.s over the roots, letting the edge come just below the seed, slipping in the slivers of wood to prevent the gla.s.s crushing the roots. Wrap the two flaps of the cloth about the seed. Pour some water in the plate and leave for development. (Fig. 12.) A day or two of waiting will show conclusively that the lengthening takes place at the tip only, or just back of the tip. Is this fact of any value to the farmer? Yes. The soft tender root tips will force their way through a mellow soil with greater ease and rapidity than through a hard soil, and the more rapid the root growth the more rapid the development of the plant. This teaches us again the lesson of deep, thorough breaking and pulverizing of the soil before the crop is planted.

We have learned that the roots grow out into the soil in search of moisture and food, which they absorb for the use of the plant. How does the root take in moisture and food? Many people think that there are little mouths at the tips of the roots, and that the food and moisture are taken in through them. This is not so, for examination with the most powerful microscopes fails to discover any such mouths.

Sprout seeds of radish, turnip or cabbage, or other seeds, on dark cloth, placed in plates and kept moist. Notice the fuzz or ma.s.s of root hairs near the ends of the tender roots of the seedlings (Fig.

13). Plant similar seed in sand or soil, and when they have started to grow pull them up and notice how difficult it is to remove all of the sand or dirt from the roots. This is because the delicate root hairs cling so closely to the soil grains. The root hairs are absorbing moisture laden with plant food from the surface of the soil particles. The root hairs are found only near the root tips. As the root grows older, its surface becomes tougher and harder, and the hairs die, while new ones appear on the new growth just back of the root tips, which are constantly reaching out after moisture and food.

The moisture gets into the root hairs by a process called osmose. The following interesting experiment will give you an idea of this process or force of osmose.

[Ill.u.s.tration: FIG. 10.

A plow stopped in the furrow, to show what it does to the roots of plants when used for after-cultivation. Notice the point of the plow under the roots.]

[Ill.u.s.tration: FIG. 11.

A corn-plant ten days after planting the seed. To show how quickly the roots reach out into the soil. Some of the roots were over 18 inches long.]

=Experiment.=--Procure a wide-mouthed bottle, an egg, a gla.s.s tube about three inches long and a quarter-inch in diameter, a candle, and a piece of wire a little longer than the tube. Remove a part of the sh.e.l.l from the large end of the egg without breaking the skin beneath.

This is easily done by gently tapping the sh.e.l.l with the handle of a pocket-knife until it is full of small cracks, and then, with the blade of the knife, picking off the small pieces. In this way remove the sh.e.l.l from the s.p.a.ce about the size of a nickel. Remove the sh.e.l.l from the small end of the egg over a s.p.a.ce about as large as the end of the gla.s.s tube. Next, from the lower end of the candle cut a piece about one-half inch long. Bore a hole in this just the size of the gla.s.s tube. Now soften one end of the piece of candle with the hole in it and stick it on to the small end of the egg so that the hole in the candle comes over the hole in the egg. Heat the wire, and with it solder the piece of candle more firmly to the egg, making a water-tight joint. Place the gla.s.s tube in the hole in the piece of candle, pushing it down till it touches the egg. Then, with the heated wire, solder the tube firmly in place. Now run the wire down the tube and break the skin of the egg just under the end of the tube. Fill the bottle with water till it overflows, and set the egg on the bottle, the large end in contact with the water (Fig. 14). In an hour or so the contents of the egg will be seen rising in the gla.s.s tube. This happens because the water is making its way by osmose into the egg through the skin, which has no openings, so far as can be discovered.

If the bottle is kept supplied with water as fast as it is taken up by the egg, almost the entire contents of the egg will be forced out of the tube. In this way water in which plant food is dissolved enters the slender root hairs and rises through the plant.

=Experiment.=--This process of osmose may also be shown as follows (Fig. 15): Remove the sh.e.l.l from the large end of an egg without breaking the skin, break a hole in the small end of the egg and empty out the contents of the egg; rinse the sh.e.l.l with water. Fill a wide-mouthed bottle with water colored with a few drops of red ink.

Fill the egg-sh.e.l.l partly full of clear water and set it on the bottle of colored water. Colored water will gradually pa.s.s through the membrane of the egg and color the water in the sh.e.l.l. Prepare another egg in the same way, but put colored water in the sh.e.l.l and clear water in the bottle. The colored water in the sh.e.l.l will pa.s.s through the skin and color the water in the bottle. Sugar or salt may be used in place of the red ink, and their presence after pa.s.sing through the membrane may be detected by taste.

CONDITIONS NECESSARY FOR ROOT GROWTH

We have learned some of the things that the roots do for plants and a little about how the work is done. The next thing to find out is:

What conditions are necessary for the root to do its work?

We know that a part of the work of the root is to penetrate the soil and hold the plant firmly in place. Therefore, it needs a firm soil.

We know that the part of the root which penetrates the soil is tender and easily injured. Therefore, for rapid growth the root needs a mellow soil.

We know that part of the work of the root is to take moisture from the soil. Therefore, it needs a moist soil.

We know that part of the work of the root is to take food from the soil. Therefore, it needs a soil well supplied with plant food.

We know that roots stop their work in cold weather. Therefore, they need a warm soil.

Another condition needed by roots we will find out by experiment.

=Experiment.=--Take two wide-mouthed clear gla.s.s bottles (Fig. 16); fill one nearly full of water from the well or hydrant; fill the other bottle nearly full of water that has been boiled and cooled; place in each bottle a slip or cutting of Wandering Jew (called also inch plant, or tradescantia, and spiderwort), or some other plant that roots readily in water. Then pour on top of the boiled water about a quarter of an inch of oil--lard oil or cotton-seed oil or salad oil.

This is to prevent the absorption of air. In a few days roots will appear on the slip in the hydrant water, while only a very few short ones, if any, will appear in the boiled water, and they will soon cease growing. Why is this? To answer this question, try another experiment. Take two bottles, filled as before, one with hydrant water and the other with boiled water; drop into each a slip of gla.s.s or a spoon or piece of metal long enough so that one end will rest on the bottom and the other against the side of the bottle, and let stand for an hour or so (Fig. 17). At the end of that time bubbles of air will be seen collecting on the gla.s.s or spoon in the hydrant water, but none in the boiled water. This shows us that water contains more or less air, and that boiling the water drives this air out. The cutting in the boiled water did not produce roots because there was no air in it and the oil kept it from absorbing any.

=Experiment.=--Into some tumblers of moist sand put cuttings of several kinds of plants that root readily (Fig. 18), geranium, tradescantia, begonia, etc. Put cuttings of same plants into tumblers filled with clay that has been wet and stirred very thoroughly, until it is about the consistency of cake batter. Keep the sand and puddled clay moist; do not allow the clay to crack, which it will do if it dries. The cuttings in the sand will strike root and grow, while most, if not all, those in the clay will soon die. The reason for this is that the sand is well ventilated and there is sufficient air for root development, while the clay is very poorly ventilated, and there is not sufficient air for root growth.

These experiments show us that to develop and do their work roots need air or a well-ventilated soil.

We have found the conditions which are necessary for the growth and development of plant roots, namely:

A firm, mellow soil.

A moist soil.

A soil supplied with available plant food.

A warm soil.

A ventilated soil.

These are the most important facts about plant growth so far as the plant grower is concerned. In other words, these conditions which are necessary for root growth and development are the most important truths of agriculture, or they are the foundation truths or principles upon which all agriculture is based. Having found these conditions, the next most important step is to find out how to bring them about in the soil, or, if they already exist, how to keep them or to improve them. This brings us, then, to a study of soils.

[Ill.u.s.tration: FIG. 12.

To show where growth in length of the root takes place. Forty hours before the photograph was taken the tip of the root was inch from the lowest thread. The gla.s.s cover was taken from this in order to get a good picture of the root.]

[Ill.u.s.tration: FIG. 13.

Radish seeds sprouted on dark cloth. To show root hairs.]

[Ill.u.s.tration: FIG. 14.

To show how water gets into the roots of plants. Water pa.s.sed up into the egg through the skin, or membrane, and forced the contents up the gla.s.s tube until it began to overflow.]

[Ill.u.s.tration: FIG. 15.

To show osmose (see page 19).]

CHAPTER III

SOILS