ROOTS
USES OF ROOTS TO PLANTS
Of what use are roots to plants, or, what work do they perform for the
plants?
If the reader has ever tried to pull up weeds or other plants he will
agree that one function of the roots of plants is to hold them firmly
in place while they are growing.
=Experiment.=--Pull two plants from the soil, shake them free of
earth, and place the roots of one in water and expose the roots of the
other to the air. Notice that the plant whose roots are exposed to the
air soon wilts, while the one whose roots were placed in water keeps
fresh. You have noticed how a potted plant will wilt if the soil in
the pot is allowed to become dry (see Fig. 4), or how the leaves of
corn and other plants curl up and wither during long periods of dry
weather. It is quite evident roots absorb moisture from the soil for
the plant.
=Experiment.=--Plant some seeds in tumblers or in boxes filled with
sand and in others filled with good garden soil. Keep them well
watered and watch their progress for a few weeks (see Fig. 5). The
plants in the garden soil will grow larger than those in the sand. The
roots evidently must get food from the soil and those in the good
garden soil get more than those in the poorer sand. Another important
function of plant roots then is to take food from the soil for the
plant.
You know how thick and fleshy the roots of radishes, beets and turnips
are. Well, go into the garden and see if you can find a spring radish
or an early turnip that has sent up a flower stalk, blossomed and
produced seeds. If you are successful, cut the root in two and notice
that instead of being hard and fleshy like the young radish or turnip,
it has become hollow, or soft and spongy (see Fig. 6). Evidently the
hard, fleshy young root was packed with food, which it afterwards gave
up to produce flower stalk and seeds.
A fourth use of the root, then, is to store food for the future use of
the plant.
=Experiment.=--Plant a sweet potato or place it with the lower end in
a tumbler of water and set it in a warm room. Observe it from day to
day as it puts out new shoots bearing leaves and roots (see Fig. 7).
Break these off and plant them in soil and you have a number of new
plants. If you can get the material, repeat this experiment with roots
of horse-radish, raspberry, blackberry or dahlia. From this we see
that it is the work of some roots to produce new plants. This function
of roots is made use of in propagating or obtaining new plants of the
sweet potato, horse-radish, blackberry, raspberry, dahlia and other
plants.
[Illustration: FIG. 4.
To show that plant-roots take water from the soil, the plants in _A_
are suffering from thirst. _B_ has sufficient water.]
[Illustration: FIG. 5.
To show that plant roots take food from the soil. Both boxes were
planted at the same time.]
[Illustration: FIG. 6.
A radish root, from which the stored food has been used to help
produce a crop of seeds. Notice the spindle shaded seed-vessels.]
[Illustration: FIG. 7.
A sweet-potato root producing new plants.]
We have now learned five important things that roots do for plants,
namely:
Roots hold plants firmly in place.
They absorb water from the soil for the plants.
They absorb food from the soil for the plants.
Some roots store food for the future use of the plant.
Some roots produce new plants.
How do the roots do this work? To answer this question it will be
necessary to study the habit of growth of the roots of our plants.
HABIT OF GROWTH OF ROOTS
The proper place to begin this study is in the field or garden. So we
will make another excursion, and this time we will take with us a
pick-axe or mattock, a shovel or two, a sharp stick, a quart or
half-gallon pitcher, and several buckets of water. Arrived in the
field, we will select a well-developed plant, say, of corn, potato or
cotton. Then we will dig a hole about six feet long, three feet wide,
and five or six feet deep, close to the plant, letting one side come
about four or five inches from the base of the plant. It will be well
to have this hole run across the row rather than lengthwise with it.
Then with the pitcher pour water about the base of the plant and wash
the soil away from the roots. Gently loosening the soil with the
sharpened stick will hasten this work. In this way carefully expose
the roots along the side of the hole, tracing them as far as possible
laterally and as deep as possible, taking care to loosen them as
little as possible from their natural position. (See Figs. 8 and 9.)
Having exposed the roots of one kind of plant to a width and depth of
five or six feet, expose the roots of six or eight plants of different
kinds to a depth of about eighteen inches. As this may require more
time than we can take for it in one day, it will be well to cover the
exposed roots with some old burlaps or other material until we have
them all ready, in order to keep them from drying and from injury.
When all is ready we will study the root system of each plant and
answer these four questions:
In what part of the soil are most of the roots?
How deep do they penetrate the soil?
How near do they come to the surface of the soil?
How far do they reach out sidewise or laterally from the plant?
To the first question, "In what part of the soil are most of the
roots?" you will give the following answers: "In the upper layer." "In
the surface soil." "In the softer soil." "In the darker soil." "In the
plowed soil."
These are all correct, but the last is the important one. Most of the
roots will be formed in that part of the soil that has been plowed or
spaded.
The second question, "How deep do the roots penetrate the soil?" is
easily answered. Roots will be found penetrating the soil to depths of
from two to six feet or more. (See Fig. 8.) The author has traced the
roots of cowpea and soy bean plants to depths of five and six feet,
corn roots four and five feet, parsnips over six feet. The
sweet-potato roots illustrated in Fig. 8 penetrated the soil to a
depth of over five feet. The roots of alfalfa or lucern have been
traced to depths of from thirteen to sixteen feet or more.
How near to the surface of the soil do you find roots? Main side or
lateral roots will be found within two or three inches of the surface,
and little rootlets from these will be found reaching up as near the
surface as there is a supply of moisture. After a continued period of
wet weather, if the soil has not been disturbed, roots will be found
coming to the very surface and even running along the top of the soil.
As to the fourth question, How far do roots reach out sidewise or
laterally from the plant? you will find roots extending three, four,
five and even six or more feet from the plant. They have numerous
branches and rootlets, which fill all parts of the upper soil. Tree
roots have been found thirty or forty feet in length.
We started on this observation lesson to find out something about the
habit of growth of roots, so that we could tell how the roots do their
work for the plant. But before going on with that question, let us
stop right here and see whether we cannot find some very important
lessons for the farmer and plant grower from what we have already
seen. Is a knowledge of these facts we have learned about roots of any
value to the farmer? Let us examine each case and see.
Of what value is it to the farmer to know that the larger part of the
roots of farm plants develop in that part of the soil that has been
plowed or spaded? It tells him that plowing tends to bring about the
soil conditions which are favorable to the growth and development of
roots. Therefore, the deeper he plows, the deeper is the body of the
soil having conditions best suited for root growth, and the larger
will be the crop which grows above the soil.
Of what value is it to the farmer to know that the roots of farm
plants penetrate to depths of five or six feet in the soil? To answer
this question it will be necessary for us to know something of the
conditions necessary for root growth. So we will leave this till
later.
Of what value is it to the farmer to know that many of the roots of
his farm plants come very near the surface of the soil? It tells him
that he should be careful in cultivating his crop to injure as few of
these roots as possible. In some parts of the country, particularly in
the South, the tool commonly used for field cultivation is a small
plow. This is run alongside of the row, throwing the soil from the
crop, and then again throwing the soil to the crop. Suppose we
investigate, and see how this affects the roots of the crop.
[Illustration: FIG. 8.
Sweet potato roots. The great mass of the roots is in the plowed soil.
Many of them reach out 5 to 7 feet from the plant. Some reach a depth
of more than 5 feet, and others come to the very surface of the soil.]
[Illustration: 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
glass 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 glass, 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 glass 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 glass. 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 glass over the
roots, letting the edge come just below the seed, slipping in the
slivers of wood to prevent the glass 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 mass 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.
[Illustration: 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.]
[Illustration: 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 glass 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
shell from the large end of the egg without breaking the skin beneath.
This is easily done by gently tapping the shell 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 shell from the space about the size of a nickel. Remove the shell
from the small end of the egg over a space about as large as the end
of the glass 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
glass 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 glass 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 glass 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 shell 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 shell with water. Fill a
wide-mouthed bottle with water colored with a few drops of red ink.
Fill the egg-shell partly full of clear water and set it on the bottle
of colored water. Colored water will gradually pass through the
membrane of the egg and color the water in the shell. Prepare another
egg in the same way, but put colored water in the shell and clear
water in the bottle. The colored water in the shell will pass 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 passing 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 glass 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 glass 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 glass 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.
[Illustration: 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 ¼ inch from
the lowest thread. The glass cover was taken from this in order to get
a good picture of the root.]
[Illustration: FIG. 13.
Radish seeds sprouted on dark cloth. To show root hairs.]
[Illustration: FIG. 14.
To show how water gets into the roots of plants. Water passed up into
the egg through the skin, or membrane, and forced the contents up the
glass tube until it began to overflow.]
[Illustration: FIG. 15.
To show osmose (see page 19).]