Chapter VII: Part I: Teachers' Leaflets (4)

Some of the vapor of the air, on condensing, gathers on solid objects like grass, or glass; but some, as fog, floats about in the air. Really this, too, is often gathered around solid objects. Floating about in the air are innumerable bits of "dust" which you can see dancing about in the sunlight when a sunbeam enters a dark room. Some of these "dust" particles are actual dust from the road, but much of it is something else, as the pollen of plants, microbes, and the solid bits produced by the burning of wood or coal.

Each bit serves as a tiny nucleus on which the vapor condenses; and so the very "dust" in the air aids in the formation of rain by giving something solid around which the liquid can gather. The great amount of dust in the air near the great city of London is believed to be one of the causes for the frequent fogs of that city.

That there is dust in the air, and that the rain removes it, is often proved when a dull hazy air is changed to a clear, bright air by a summer shower. Watch to find instances of this. Indeed, after such a hazy day, when the rain drops first begin to fall, if you will let a few drops fall upon a sheet of clean white paper, and then dry it, you will find the paper discolored by the dust that the rain brought with it. So the rain purifies the air by removing from it the solids that are floating in it.

These are only a few of the things of interest that you can see for yourself by studying the air. Watch the sky; it is full of interest. See what you can observe for yourself. Watch especially the clouds, for they are not only interesting but beautiful (Fig. 17). Their forms are often graceful, and they change with such rapidity that you can notice it as you watch them. Even in the daytime the colors and shadows are beautiful; but at sunrise and at sunset the clouds are often changed to gorgeous banks of color.

Watch the clouds and you will be repaid; look especially for the great piles of clouds in the east during the summer when the sun is setting (Fig. 18). Those lofty banks, tinged with silver and gold, and rising like mountains thousands of feet into the air, are really made of bits of fog and mist. Among them vapor is still changing to water and rain drops are forming, while violent currents are whirling the drops about, and perhaps lifting them to such a height that they are being frozen into hailstones. Far off to the east, beneath that cloud, rain is falling in torrents, lightning is flashing and thunder crashing, though you cannot hear it because it is so far away.

You see the storm merely as a brightly lighted and beautifully colored cloud mass in the sky; but the people over whom it is hanging find it a threatening black cloud, the source of a furious wind, a heavy rain, and the awe-inspiring lightning. To them it may not be beautiful, though grand in the extreme; and so, too, when the summer thunder shower visits you in the early evening, you may know that people to the west of you are probably looking at its side and top and admiring its beauty of form and color.

The storm passes on, still to the eastward, and finally the cloud mass entirely disappears beneath the eastern horizon; but if you watch, you will see signs that it is still there, though out of sight; for in the darkness of the night you can see the eastern horizon lighted by little flashes, the source of which cannot be seen. You call it "heat lightning," but it is really the last signal that we can see of the vanishing thunder storm, so far away that the sound of the crashing thunder cannot be heard.

You watch the mysterious flashes; they grow dimmer and dimmer and finally you see them no more. Our summer shower is gone. It has done what thousands of others have done before, and what thousands of others will do in the future. It has started, moved off, and finally disappeared from sight; and as it has gone it has told us a story. You can read a part of this story if you will; and in reading it will find much that interests.

LEAFLET VII.

A SNOW STORM.[9]

BY ANNA BOTSFORD COMSTOCK.

The snow had begun in the gloaming,
And busily all the night
Had been heaping field and highway
With a silence deep and white.
Every pine and fir and hemlock
Wore ermine too dear for an earl,
And the poorest twig on the elm-tree
Was ridged inch deep with pearl.
From sheds new-roofed with Carrara
Came Chanticleer's muffled crow
The stiff rails were softened to swan's-down
And still fluttered down the snow.
--_Lowell._

[9] Home Nature-Study Course, December, 1903.

The storm which Lowell describes so delightfully is the first soft, gentle snow fall that comes in November or early December. "The silence deep and white" settles like a benediction over the brown, uneven landscape, and makes of it a scene of enchantment. Very different from this is the storm that comes when the winter cold is most severe and winter winds most terrific. Then the skies are as white as the fields, with never a sign of blue; if the sun appears at all, it shines cold instead of warm, and seems but a vague white spot behind the veil of upward, downward whirling snowflakes; the wild wind takes the "snow dust" in eddies across the fields and piles it at the fences in great drift billows with overhanging crests. On such a day the snow is so cold and dry, the clouds so low and oppressive, the bare trees so brown and bleak, that we shiver even though we gaze on the dreary scene from the window of a warm and comfortable room.

But another change is sure to come. Some February day the wind will veer suddenly to the south and breathe warm thawing breaths over the white frozen world. Then will the forests appear in robes of vivid blue-purple against the shining hills; and in the mornings the soft blue of the horizon will shade upward into rose-color and still upward into yellow and beryl green; these hues are never seen on the forest or in the sky except when the snow covers the earth to the horizon line. The eye that loves color could ill afford to lose from the world the purples and blues which bring contrast into the winter landscape.

The snow storm to our limited understanding, begins with a miracle--the miracle of crystallization. Why should water freezing freely in the air be a part of geometry, the six rays of the snow crystal growing at an angle one to another, of sixty degrees? Or as if to prove geometry divine beyond cavil, sometimes the rays include angles of twice sixty degrees. Then why should the decorations of the rays assume thousands of intricate, beautiful forms, each ray of a flake ornamented exactly like its five sisters? And why should the snowflake formed in the higher clouds of the upper air be tabular in shape but still, in cross section, show that it is built on the plan of six radii? Look at it as we will, the formation of a crystal is a beautiful mystery and is as unfathomable as is the mystery of life.

I am indebted to the courtesy of Mr. R. G. Allen, Section Director for New York of the U. S. Weather Bureau, for suggestions in making out the following questions. The beautiful pictures of snow crystals illustrating this lesson were made from photographs taken by Mr. W. A. Bentley of Jericho, Vt. It is our desire to interest all teachers in the natural history of a snow storm, to the end that "they may love the country better and be content to live therein."

A thermometer hung in a sheltered, open place away from the warmth of the house is a necessary preliminary to the proper observation of the phenomena of a snow storm.

Dark woolen cloth is the best medium on which to catch and observe snow crystals.

QUESTIONS ON A SNOW STORM.

1. What causes snow?

2. At what temperature do snow crystals form?

3. How do the clouds appear before a snow storm?

4. What is the temperature of the air before the storm?

5. What is the direction of the wind before the storm?

6. Does the storm come from the same direction as the wind?

7. What are the conditions of the wind and temperature when the snow crystals are most perfect in form?

8. What are these conditions when the snow crystals are matted together in great flakes?

9. What are these conditions when the snow crystals appear sharp and needle-like?

10. Are the snow crystals of the same storm similar in structure and decoration?

11. What is the difference in structure between a snowflake and a hail stone?

12. What is sleet?

13. What is the difference between hoar frost and snow?

14. Does the temperature rise or fall during a snow storm?

15. Is it colder or warmer after a snow storm has passed than it was before it began?

16. What are the conditions of weather which cause a blizzard?

17. Why does a covering of snow prevent the ground from freezing so severely as it would if bare?

18. Why is snow a bad conductor of heat?

19. Pack snow in a quart cup until it is full and let it melt; then tell how full the cup is of water. What do you infer from this?

20. Have you ever observed the grass to be green beneath snow drifts? Tell why.

21. Does snow evaporate as well as melt?

22. How does snow benefit the farmer and the fruit grower?

23. Do the snow storms in your locality come from one general direction all winter?

LEAFLET VIII.

A HANDFUL OF SOIL: WHAT IT IS.[10]

BY R. S. TARR.

[10] Nature-Study Quarterly, No. 2: Leaflet 15.

Wind drifts a seed from the parent plant until it settles to the ground, perhaps in a field or by the roadside, or even in the schoolyard. There it remains through the long winter; but with the return of spring, encouraged by the warm sunlight, the seed awakens from its dormant condition, breaks open the seed-cover and sends leaves into the air and roots into the ground. No one planted the seed; yet the plant has made its way in the world and it thrives until it has given to other seeds the same opportunity to start in life.

Had the seed fallen upon a board or a stone it might have sent out leaves and roots; but it could never have developed into a plant, for something necessary would have been lacking. What is there in the soil that is so necessary to the success of plant life? How has it come to be there? What is this soil that the plants need so much? These are some of the questions which we will try to answer.

One readily sees that the soil furnishes a place in which the plants may fix themselves,--an anchorage, as it were. It is also easy to see that from the soil the plants obtain a supply of water; and, moreover, that this water is very necessary, for the vegetation in a moist country suffers greatly in time of drought, and few plants are able to grow in a desert region because there is so little water. You can make a desert in the schoolroom and contrast it with moist soil by planting seeds in two dishes of soil, watering one, but furnishing no water to the other.

That water is necessary to plants is also proved by the plant itself. The sap and the moisture which may be pressed out of a grass stem or an apple are principally water taken from the soil by the roots. But there is more than water, for the juice of an apple is sweet or sour, while the sap and juice of other plants may be sweet or bitter. There are substances dissolved in the water.

It is these dissolved substances that the plants need for their growth, and they find them ready for use in the soil. There is a plant-food which the roots seek and find, so that every plant which sends roots into the soil takes something from it to build up the plant tissue. The sharp edges of some sedges, which will cut the hand like a dull knife, and the wood ashes left when a wood fire is burned, represent in part this plant-food obtained from the soil.

Let us take a handful of soil from the field, the schoolyard, or the street and examine it. We find it to be dirt that "soils" the hands; and when we try to brush off the dirt, we notice a gritty feeling that is quite disagreeable. This is due to the bits of mineral in the soil; and that these are hard, often harder than a pin, may often be proved by rubbing soil against a piece of glass, which the hard bits will often scratch, while a pin will not.

Study this soil with the eye and you may not see the tiny bits, though in sandy soils one may easily notice that there are bits of mineral. Even fine loamy and clay soils, when examined with a pocket lens or a microscope, will be found to be composed of tiny fragments of mineral. It is evident that in some way mineral has been powdered up to form the soil; and since the minerals come from rocks, it is the rocks that have been ground up. That powdered rock will make just such a substance as soil may be proved by pounding a pebble to bits, or by collecting some of the rock dust that is made when a hole is drilled in a rock. Much the same substance is ground from a grindstone when a knife is sharpened on it, making the water muddy like that in a mud hole.

It will be an interesting experiment to reduce a pebble to powder and plant seeds in it to see whether they will grow as well as in soil; but in preparing it try to avoid using a sandstone pebble, because sandy soils are never very fertile.

Not only is soil made up of bits of powdered rock, but it everywhere rests upon rock (Fig. 25). Some consider soil to be only the surface layers in which plants grow; but really this is, in most places, essentially the same as the layers below, down even to the very rock, so that we might call it all soil; though, since a special name, _regolith_ (meaning stone blanket), has been proposed for all the soft, soil-like rock-cover, we may speak of it as regolith and reserve the word soil for the surface layers only.

In some places there is no soil on the bare rocks; elsewhere the soil-cover is a foot or two in depth; but there are places where the regolith is several hundred feet deep. In such places, even the wells do not reach the bed rock; nor do the streams cut down to it; but even there, if one should dig deep enough, he would reach the solid rock beneath.

How has the hard rock been changed to loose soil? One of the ways, of which there are several, may be easily studied whenever a rock has been exposed to the air. Let us go to a stone wall or among the pebbles in a field, for instance, and, chipping off the surface, notice how different the inside is from the outside. The outer crust is rusted and possibly quite soft, while the interior is harder and fresher. Many excellent examples of this may be found in any stony field or stone wall.

As hard iron rusts and crumbles to powder when exposed to the weather; so will the minerals and the rocks decay and fall to bits; but rocks require a very much greater time for this than does iron. It happens that the soil of New York has not been produced by the decay of rock; and, therefore, although the soils in many parts of the world have been formed in this way, we will not delay longer in studying this subject now, nor in considering the exact way in which rocks are enabled to crumble.

Another way in which rocks may be powdered may be seen in most parts of New York. The rains wash soil from the hillsides causing the streams to become muddy. In the streams there are also many pebbles, possibly the larger fragments that have fallen into the stream after having been broken from the ledges. The current carries these all along down the stream, and, as they go, one piece striking against another, or being dragged over the rocks in the stream bed, the pebbles are ground down and smoothed (Fig. 23), which means, of course, that more mud is supplied to the stream, as mud is furnished from a grindstone when a knife or scythe is being sharpened on it. On the pebbly beaches of the sea or lakeshore much the same thing may be seen; and here also the constant grinding of the rocks wears off the edges until the pebbles become smooth and round.

Supplied with bits of rock from the soil, or from the grinding up of pebbles and rocks along its course, the stream carries its load onward, perhaps to a lake, which it commences to fill, forming a broad delta of level and fertile land, near where the stream enters the lake. Or, possibly, the stream enters the sea and builds a delta there, as the Mississippi river has done.

But much of the mud does not reach the sea. The greatest supply comes when the streams are so flooded by heavy rains or melting snows that the river channel is no longer able to hold the water, which then rises above the banks, overflowing the surrounding country. Then, since its current is checked where it is so shallow, the water drops some of its load of rock bits on the flood-plain, much as the muddy water in a gutter drops sand or mud on the sidewalk when, in time of heavy rains, it overflows the walk.

Many of the most fertile lands of the world are flood-plains of this kind, where sediment, gathered by the streams farther up their courses, is dropped upon the flood-plains, enriching them by new layers of fertile soil. One does not need to go to the Nile, the Yellow, or the Mississippi for illustrations of this; they abound on every hand, and many thousands of illustrations, great and small, may be found in the State of New York. Doubtless you can find one.

There are other ways in which soils may be formed; but only one more will be considered, and that is the way in which most of the soils of New York have been made. To study this let us go to a cut in the earth, such as a well or a stream bank (Figs. 22 and 24). Scattered through the soil numerous pebbles and boulders will doubtless be found; and if these are compared with the bed rock of the country, which underlies the soil (Fig. 22), some of them will be found to be quite different from it. For instance, where the bed rock is shale or limestone, some of the pebbles will no doubt be granite, sandstone, etc. If you could explore far enough, you would find just such rocks to the north of you, perhaps one or two hundred miles away in Canada; or, if your home is south of the Adirondacks, you might trace the pebbles to those mountains.

On some of these pebbles, especially the softer ones, such as limestone, you will find scratches, as if they had been ground forcibly together (Fig. 25). Looking now at the bed rock in some place from which the soil has been recently removed, you will find it also scratched and grooved (Fig. 26); and if you take the direction of these scratches with the compass, you will find that they extend in a general north and south direction, pointing, in fact, in the same direction from which the pebbles have come.

All over northeastern North America and northwestern Europe the soil is of the same nature as that just described. In our own country this kind of soil reaches down as far as the edge of the shaded area in the map (Fig. 27), and it will be noticed that all of New York is within that area excepting the extreme southwestern part near the southern end of Chautauqua lake.

Not only is the soil peculiar within this district, but there are many small hills of clay or sand, or sometimes of both together (Figs. 33 and 34). They rise in hummocky form and often have deep pits or kettle-shaped basins between, sometimes, when the soil is clayey enough to hold water, containing tiny pools. These hills extend in somewhat irregular ranges stretching across the country from the east toward the west. The position of some of these ranges is indicated on the map (Fig. 27).

For a long time people wondered how this soil with its foreign pebbles and boulders, altogether called "drift," came to be placed where it is; they were especially puzzled to tell how the large boulders, called erratics (Fig. 21), should have been carried from one place to another. It was suggested that they came from the bursting of planets, from comets, from the explosion of mountains, from floods, and in other ways equally unlikely; but Louis Agassiz, studying the glaciers of the Alps and the country round about, was impressed by the resemblance between the "drift" and the materials carried by living glaciers.

Agassiz, therefore, proposed the hypothesis that glaciers had carried the drift and left it where we now find it; but for many years his glacial hypothesis met with a great deal of opposition because it seemed impossible that the climate could have changed so greatly as to cover what is now a temperate land with a great sheet of ice. Indeed, even now, although all who have especially studied the subject are convinced, many people have not accepted Agassiz's explanation, just as years ago, long after it was proved that the earth rotated each day, many people still believed that it was the sun, not the earth, that was moving.

The glacial explanation is as certain as that the earth rotates. For some reason, which we do not know, the climate changed and allowed ice to cover temperate lands, as before that time the climate had changed so as to allow plants like those now growing as far south as Virginia to live in Greenland, now ice covered. When the ice of the glacier melted away it left many signs of its presence; and when the temperate latitude plants grew in Greenland they left seeds, leaves and tree trunks which have been imbedded in the rocks as fossils. One may now pick the leaves of temperate climate trees from the rocks beneath a great icecap.

To one who studies them, the signs left by the glacier are as clear proof as the leaves and seeds. From these signs we know that the climate has changed slowly, but we have not yet learned why it changed.

There are now two places on the earth where vast glaciers, or ice sheets, cover immense areas of land, one in the Antarctic, a region very little known, the other in Greenland, where there is an ice sheet covering land having an area more than ten times that of the State of New York. Let us study this region to see what is being done there, in order to compare it with what has been done in New York.

In the interior is a vast plateau of ice, in places over 10,000 feet high, a great icy desert (Fig. 28), where absolutely no life of any kind, either animal or plant, can exist, and where it never rains, but where the storms bring snow even in the middle of summer. Such must have been the condition in northeastern America during the glacial period.

This vast ice sheet is slowly moving outward in all directions from the elevated center, much as a pile of wax may be made to flow outward by placing a heavy weight upon the middle. Moving toward the north, east, south and west, this glacier must of course come to an end somewhere. In places, usually at the heads of bays, the end is in the sea, as the end of our glacier must have been off the shores of New England. From these sea-ends, icebergs constantly break off; these floating away toward the south, often reach, before they melt, as far as the path followed by the steamers from the United States to Europe. Between the bays where the glacier ends in the sea, the ice front rests on the land (Fig. 29), as it did over the greater part of New York and the states further west. There it melts in the summer, supplying streams with water and filling many small ponds and lakes. The front stands there year after year, sometimes moving a little ahead, again melting further back so as to reveal the rocks on which it formerly rested.

The bed rock here is found to be polished, scratched and grooved just like the bed-rock in New York; and the scratches extend in the direction from which the ice moves. Resting on the rock are boulders and pebbles (Fig. 22), sometimes on the bare rock, sometimes imbedded in a clay as they are in the drift. As we found when studying the soil in our own region, so here the pebbles are often scratched, and many of them are quite different from the rock on which they rest.

Going nearer to the ice we find the lower part loaded with pebbles, boulders and bits of clay very like those on the rocks near by. Fig. 30 shows one of these, scratched and grooved, which I once dug from the ice of this very glacier. The bottom of the ice is like a huge sandpaper, being dragged over the bed rock with tremendous force. It carries a load of rock fragments, and as it moves secures more by grinding or prying them from the rocks beneath. These all travel on toward the edge of the ice, being constantly ground finer and finer as wheat is ground when it goes through the mill. Indeed the resemblance is so close that the clay produced by this grinding action is often called _rock flour_.

Dragged to the front of the ice, the rock bits, great and small, roll out as the ice melts, some, especially the finest, being carried away in the water, which is always muddy with the rock flour it carries; but much remains near the edge of the ice, forming a _moraine_ (Figs. 31 and 32). This moraine, dumped at the edge of the glacier, very closely resembles the hummocky hills of New York (Figs. 33 and 34), mentioned above, which are really moraines formed at the ice-edge during the glacial period. While their form is quite alike, the New York moraines are generally less pebbly than the Greenland moraines, because the Greenland glacier carries less rock flour than did the glacier which covered New York.

In the Greenland glacier, as you can see in Fig. 31, there is much dirt and rock; in the glacier of the glacial period there was even more. When it melted away the ice disappeared as water, but the rock fragments of course fell down upon the rock beneath and formed soil. If over a certain region, as for instance over your home, the ice carried a great load of drift, when this gradually settled down, as the ice melted, it formed a deep layer of soil; but if the glacier had only a small load a shallow soil was left. Again, if the ice front remained for a long time near a certain place, as near your home, it kept bringing and dumping rock fragments to form moraines, which, of course, would continue to grow higher so long as the ice dumped the rock fragments, much as a sand pile will continue to grow higher so long as fresh loads are brought and dumped.

There are other causes for differences in the glacial soils, but most of them cannot be considered here. One of them is so important, however, that it must be mentioned. With the melting of so much ice, vast floods of water were caused, and these came from the ice, perhaps in places where there are now no streams, or at best only small ones. These rapid currents carried off much of the rock flour and left the coarser and heavier sand, gravel, or pebbles, the latter often well rounded, with the scratches removed by the long-continued rolling about in the glacial stream bed.

One often finds such beds of sand or gravel in different parts of the State, telling not only of ice where it is now absent, but of water currents where is now dry land. The rock flour was in some cases carried to the sea, elsewhere to lakes, or in still other places deposited in the flood-plains of the glacier-fed rivers. Now some of this rock flour is dug out to make into bricks.

Enough has been said to show that the soils of New York were brought by a glacier, and to point out that there are many differences in thickness as well as in kind and condition of the soil. The agriculture of the State is greatly influenced by these differences. In some cases one part of a farm has a deep, rich soil, another part a barren, sandy, pebbly or boulder-covered soil (Fig. 21), while in still another part the bed rock may be so near the surface that it does not pay to clear the forest from it. Moreover, some farms are in hummocky moraines, while others, near by, are on level plains (Fig. 34), where a broad glacial stream built up a flood-plain in a place where now the stream is so small that it never rises high enough to overflow the plain.

There are even other differences than these, and one who is familiar with a region is often puzzled to explain them; but they are all due to the glacier or to the water furnished by its melting, and a careful study by a student of the subject of Glacial Geology will serve to explain them. Each place has had peculiar conditions and it would be necessary to study each place much more carefully than has been done here in order to explain all the differences.

Not only is agriculture influenced greatly by the differences in the soil from place to place, but also by the very fact that they are glacial soils. Being made up of partly ground-up rock fragments the soils are often stony and difficult to till. Unlike the soil of rock decay, the particles of which the glacial soil is made have been derived by mechanical grinding, not by chemical decay and disintegration. There has been less leaching out of the soluble compounds which make plant foods. These are stored up in the rock fragments ready for use when decay causes the proper changes to produce the soluble compounds which plants require.

Slowly the glacial soils are decaying, and, as they do so, are furnishing plant-food to the water which the roots greedily draw in. So the glacial soil is not a mere store house of plant-food, but a manufactory of it as well, and glacial soils are therefore "strong" and last for a long time. That decay is going on, especially near the surface, may often be seen in a cut in the soil, where the natural blue color of the drift is seen below, while near the surface the soil is rusted yellow by the decay of certain minerals which contain iron.

Few materials on the earth are more important than the soil; it acts as the intermediary between man and the earth. The rocks have some substances locked up in them which animals need; by decay, or by being ground up, the rocks crumble so that plants may send roots into them and extract the substances needed by animals. Gifted with this wonderful power the plants grow and furnish food to animals, some of which is plant-food obtained from the rocks; and so the animals of the land, and man himself, secure a large part of their food from the rocks. It is then worth the while to stop for a moment and think and study about this, one of the most marvelous of the many wonderful adjustments of Nature, but so common that most persons live and die without even giving it more than a passing thought.

LEAFLET IX.

A HANDFUL OF SOIL: WHAT IT DOES.[11]

BY L. A. CLINTON.

[11] Nature-Study Quarterly, No. 2: Leaflet 15, October, 1899.

The more one studies the soil, the more certainly it will be found that the earth has locked up in her bosom many secrets, and that these secrets will not be given up for the mere asking. As mysterious as the soil may appear at different times, it always is governed by certain laws. These principles once understood, the soil becomes an open book from which one may read quickly and accurately.

USES OF THE SOIL.

The soil has certain offices to perform for which it is admirably fitted. The most important of these offices are:

1. To hold plants in place;
2. To serve as a source of plant-food;
3. To act as a reservoir for moisture;
4. To serve as a storehouse for applied plant-food or fertilizer.

Some soils are capable of performing all these offices, while others are fitted for only a part of them. Thus a soil which is pure sand and almost entirely deficient in the essential elements of plant-food, may serve, if located near a large city, merely to hold the plants in position while the skillful gardener feeds the plants with specially prepared fertilizers, and supplies the moisture by irrigation.

Early in the study of soils an excursion, if possible, should be made into the woods. Great trees will be seen and under the trees will be found various shrubs and possibly weeds and grass. It will be noticed that the soil is well occupied with growing plants. The surface will be found covered with a layer several inches thick of leaves and twigs. Beneath this covering the soil is dark, moist, full of organic matter, loose, easily spaded except as roots or stones may interfere, and has every appearance of being fertile.

SOIL CONDITIONS AS FOUND IN MANY FIELDS.

After examining the conditions in the forest, a study should be made of the soil in some cultivated field. It will be found that in the field the soil has lost many of the marked characteristics noticed in the woodland. In walking over the field, the soil will be found to be hard and compact. The surface may be covered with growing plants, for if the seeds which have been put into the soil by the farmer have not germinated and the plants made growth, nature has quickly come to the rescue and filled the soil with other plants which we commonly call weeds. It is nature's plan to keep the soil covered with growing plants, and from nature we should learn a lesson. The field soil, instead of being moist, is dry; instead of being loose and friable, it is hard and compact, and it appears in texture entirely different from the woodland soil. The cause of the difference is not hard to discover. In the woods, nature for years has been building up the soil. The leaves from the trees fall to the ground and form a covering which prevents washing or erosion, and these leaves decay and add to the humus, or vegetable mould, of the soil. Roots are constantly decaying and furnish channels through the soil and permit the circulation of air and water.

In the field, nature's lesson has been disregarded and too often the whole aim seems to be to remove everything from the soil and to make no returns. Consequently the organic matter, or humus, has been used up; the tramping of the horses' feet has closed the natural drainage canals; after the crop is removed, the soil is left naked during the winter and the heavy rains wash and erode the surface, and remove some of the best plant-food. After a few years of such treatment, the farmer wonders why the soil will not produce as liberally as it did formerly.

_Experiment No. 1._--The fact that there is humus, or vegetable mould, in certain soils can be shown by burning. Weigh a potful of hard soil and a potful of lowland soil, or muck, after each has been thoroughly dried. Then put the pots on the coals in a coal stove. After the soil is thoroughly burned, weigh again. Some of the difference in weight may be due to loss of moisture, but if the samples were well dried in the beginning, most of the loss will be due to the burning of the humus.

CONDITIONS WHICH AFFECT FERTILITY.

There are certain conditions which affect soil fertility and of these the most important are:

Texture;
Moisture-content;
Plant-food;
Temperature.

TEXTURE AND ITS RELATION TO FERTILITY.

By texture is meant the physical condition of the soil. Upon good texture, more than upon any other one thing, depends the productivity of the soil. When the texture is right the soil is fine, loose, and friable; the roots are able to push through it and the feeding area is enlarged. Each individual particle is free to give up a portion of its plant-food, or its film of moisture. The conditions which are found in the woods' soil are almost ideal.

_Experiment No. 2._--The importance of good texture may be well shown in the class room. Pots should be filled with a soil which is lumpy and cloddy, and other pots with the same kind of material after it has been made fine and mellow. After seeds are planted in the different pots, a careful study should be made of the length of time required for germination and of the health and vigor of the plants.

_Experiment No. 3._--The greater part of our farming lands do not present ideal conditions as regards texture. Clay soils are especially likely to be in bad condition. If samples of the various soils can be collected, as sand, loam, clay, etc., it may be clearly shown how different soils respond to the same kind of treatment. With a common garden trowel, the soils should be stirred and worked while wet, and then put away to dry. After drying, the conditions presented by the soils should be noted, also the length of time required for the soils to become dry. Whereas the sand and the loam will remain in fairly good condition when dry, the clay will have become "puddled," _i. e._, the particles will have run together and made a hard, compact mass. Thus it is found in practice that clay soils must be handled with far more care and intelligence than is required for the sand and loams, if the texture is to be kept perfect.

_Experiment No. 4._--If, in the experiment above suggested, the clay soil is mixed with leaf-mould, or humus soil, from the woods, it will be found to act very differently. The vegetable matter thus mixed with the mineral matter prevents the running together of the particles of clay.

Two principles, both important as relating to soil texture, now have been illustrated. Soils must not be worked when they are so wet that their particles will cohere, and organic matter, or humus, must be kept mixed with the mineral matter of the soil. In practical farm operations, if the soil can be made into a mud ball it is said to be too wet to work. The required amount of humus is retained in the soil by occasionally plowing under some green crop, as clover, or by applying barn manures.

Clay soils are also frequently treated with lime to cause them to remain in good condition and be more easily tilled. Lime causes the fine particles to flocculate, or to become granular, _i. e._, several particles unite to form a larger particle, and these combinations are more stable and do not so readily puddle, or run together. A mud-puddle in clay soil will remain murky until the water has evaporated entirely. Let a little water-slaked lime be mixed with the muddy water, and the particles of clay will be flocculated and will settle to the bottom; thus the water will become clear.

_Experiment No. 5._--Into two glasses of water put some fine clay soil; thoroughly stir the mixture (Fig. 35). Into one glass thus prepared put a spoonful of water-slaked lime; stir thoroughly, then allow both glasses to remain quiet that the soil may settle. Notice in which glass the water first becomes clear, and note the appearance of the sediment in each.

THE MOISTURE IN THE SOIL.

In Leaflet VI has been given the history of a thunder shower. We are not told much about the history of the water after it reaches the earth. If we go out immediately after a heavy shower, we find little streams running alongside the road. These little streams unite to make larger ones, until finally the creeks and rivers are swollen, and, if the rain was heavy enough, the streams may overflow their banks. In all these streams, from the smallest to the largest, the water is muddy. Where did this mud come from? It was washed largely from the cultivated fields, and the finest and best soil is certain to be the first to start on its voyage to the valleys or to the sea. If the farmer had only learned better the lesson from nature and kept his fields covered with plants, a large part of the loss might have been prevented. A rain gauge should be kept in every school yard, so that every shower can be measured. It can then be easily determined by the pupils how many tons of rain fall upon the school grounds, or how much falls upon an acre of land. It will be a matter of surprise that the amount is so great.

Not all the water which falls during a summer shower is carried off by surface drainage, since a considerable part sinks into the soil. As it passes down, each soil grain takes up a portion and surrounds itself with a little film of water, much as does a marble when dipped into water. If the rain continues long enough, the soil will become saturated and the water which cannot be retained, will, under the influence of gravity, sink down to the lower layers of soil until it finally reaches the level of the free water. From this free water, at varying depths in the soil, wells and springs are supplied. If the soil were to remain long saturated, seeds would not germinate, and most cultivated plants would not grow because all the air passages of the soil would be filled with water (Fig. 36). The water which sinks down deep into the soil and helps to supply our wells is called free water. That part which is held as a film by the soil particles (as on a marble) is called capillary water. After the rain is over and the sun shines, a part of the moisture which is held by the particles near the surface is lost by evaporation. The moisture which is below tends to rise to restore the equilibrium; thus there is created a current toward the surface, and finally into the air; the moisture which thus escapes aids in forming the next thunder storm.

_Experiment No. 6._--Humus enables the soil to take up and hold large quantities of water. To illustrate this, two samples of soil should be obtained, one a humus, or alluvial, soil, rich in organic matter, and the other a sandy soil. Put the two samples where they will become thoroughly air dry. Procure, say five pounds each of the dry soils, and put each into a glass tube over one end of which there is tied a piece of muslin, or fine wire gauze. From a graduated glass pour water slowly upon each sample until the water begins to drain from the bottom of the tube. In this way it can be shown which soil has the greater power of holding moisture. Both samples should then be set away to dry. By weighing the samples each day, it can be determined which soil has the greater power of retaining moisture. This experiment may be conducted not only with sand and humus, but with clay, loam, gravel, and all other kinds of soil.

_Experiment No. 7._--A finely pulverized soil will hold more film-moisture than a cloddy soil. To illustrate the importance of texture as related to moisture, soil should be secured which is cloddy, or lumpy. One tube should be filled, as heretofore described (Exp. No. 6), with the lumpy soil, and the other tube with the fine soil which results from pulverizing the lumps, equal weights of soil being used in each case. From a graduated glass pour water upon each sample until the drainage begins from the bottom. Notice which soil possesses greater power of absorbing moisture. Put the samples away to dry, and by careful weighing, each day, it can be determined which soil dries out more readily.

The prudent farmer will take measures to prevent the escape of this moisture into the air. All the film-moisture (on the soil particles) needs to be carefully conserved or saved, for the plants will need very large amounts of moisture before they mature, and they can draw their supply only from this film-moisture. We can again apply the lesson learned in the woods. The soil there is always moist; the leaves form a cover, or blanket, which prevents the evaporation of moisture. Underneath an old plank or board, the soil will be found moist. If we can break the connection between the soil and the air, we can check the escape of moisture. A layer of straw over the soil will serve to prevent the loss of moisture; yet a whole field cannot be thus covered. It has been found that the surface soil, if kept loose, say about three inches of the top soil can be made to act as a blanket or covering for the soil underneath. Although this top layer may become as dry as dust, yet it prevents the escape, by evaporation, of moisture from below. It is a matter of common observation that if tracks are made across a freshly cultivated field, the soil where the tracks are will become darker (Fig. 37). This darker appearance of the soil in the foot-marks is due to the moisture which is there rising to the surface. The implement of tillage makes the soil loose, breaking the capillary connection between the lower layers of soil and the surface; thus the upward passage of the water is checked. Where the foot-print is, the soil has been again pressed down at the surface, the particles have been crowded closer together, and capillarity is restored to the surface so that the moisture is free to escape (Fig. 38). In caring for flower-beds, or even in growing plants in a pot in the school-room, it is important that the surface of the soil be kept loose and mellow. Far better in a flower garden is a garden rake than a watering pot.

_Experiment No. 8._--To show the importance of the surface mulch, fill several pots with a sandy loam soil, putting the same weight of soil into each pot. In one pot, pack the soil firmly; in another pot, pack the soil firmly and then make the surface loose. These pots of soil may then be put away to dry; by daily weighing each it can be readily determined what effects the various methods of treatment have upon the moisture-holding power of soils.

_Experiment No. 9._--The above experiment may be varied by covering the soil in some of the pots with leaves, or straw, or paper, care being taken that the added weight of the foreign matter is properly accounted for.

SOIL TEMPERATURE.

If a kernel of corn be placed in the ground in early spring before the soil has become warm, the seed will not germinate. Abundance of moisture and oxygen may be present, but the third requisite for germination, proper temperature, is lacking. The soil is very slow to become warm in the spring, and this is due to the large amount of water which must be evaporated. During the winter and spring, the rain and melting snow have saturated the soil. The under-drainage is deficient so there is no way for the escape of the surplus water except by evaporation, and evaporation is a cooling process. A well-drained soil is thus warmer than a poorly-drained one.

The atmosphere is much quicker to respond to changes in temperature than is the soil. In the spring, the air becomes warm while the soil continues cold, and the rains which fall during this time are warmed by passing through the warm air. Then in sinking through the soil the rain-water parts with some of its heat which makes the soil warmer. During mid-summer the soil becomes very warm, and it is not affected by cool nights, as is the atmosphere. Consequently as a summer rain may be several degrees cooler than the soil, the water in passing through the soil takes up some of the heat; thus the soil conditions are made more favorable for plant growth. Therefore, soil temperature is regulated somewhat by the rainfall.

_Experiment No. 10._--The color of a soil also affects its temperature, a dark soil being warmer than a light colored soil. By having thermometers as a part of the school room equipment, interesting experiments may be conducted in determining the effect of color and moisture upon the temperature of soils.

AIR IN THE SOIL.

Although that part of the plant which we can see is entirely surrounded by air, it is also necessary that the soil be in such a condition that it can be penetrated by the air. Indeed, growth cannot begin in a soil from which the air is excluded.

_Experiment No. 11._--To prove this, put clay soil in a pot and plant seeds; then wet the surface of the soil and puddle or pack the clay while wet and watch for the seeds to germinate and grow. At the same time put seeds in another pot filled with loose, mellow, moist soil.

Frequently, after the farmer has sown his grain, there comes a heavy, beating rain, and the surface of the soil becomes so packed that the air is excluded and the seeds cannot germinate. If plants are grown in pots and the water is supplied at the top, the soil may become so hard and compact as to exclude the air and the plants will make a sickly growth. The surface soil must be kept loose so that the air can penetrate it.

On many lawns it may be noticed that the grass is not thriving. It has a sickly appearance, and even the application of fertilizer does not seem to remedy the conditions. Perhaps the ground has become so hard that the air cannot penetrate and the grass is being smothered. If the surface of the soil can be loosened with a garden rake, and clover seed sown, much good may be accomplished. The clover is a tap-rooted plant, sending its main root deep into the soil.

After the death of the plant, the root decays, and the nitrogen which is stored in it can be used as food by the other plants. Most useful of all, however, in such cases, the decay of the tap-root of the clover makes a passage deep into the soil and thus allows the air to enter. Consult Figs. 39-41.

LEAFLET X.

THE BROOK.[12]

BY J. O. MARTIN.