[Footnote 1: This section may be omitted, and the lessons begun with
Seedlings, if the teacher prefer.]
What is Botany? The pupils are very apt to say at first that it is
learning about _flowers_. The teacher can draw their attention to the fact
that flowers are only a part of the plant, and that Botany is also the
study of the leaves, the stem, and the root. Botany is the science of
_plants_. Ask them what the Geranium is. Tell them to name some other
plants. The teacher should keep a few growing plants in the schoolroom for
purposes of illustration.
Ask them what else there is in the world besides plants. By this question
the three kingdoms, animal, vegetable, and mineral, are brought up. It
will give occasion for a discussion of the earth and what it contains, the
mountains, formed of rocks and soil, the plants growing on the earth,
and the animals that inhabit it, including man. Let them name the three
kingdoms with some example of each. Which of these kingdoms contain living
things? The words _organic_ and _inorganic_ can be brought in here. An
_organ_ ([Greek: Ergon], meaning work) is any part that does a special
work, as the leaves, the stem of a plant, and the eye, the ear of animals.
An _organism_ is a living being made up of such organs. The inorganic
world contains the mineral kingdom; the organic world includes the
vegetable and animal kingdoms.
One's aim in these lessons should always be to tell the pupils as little
as possible. Try to lead them to think out these things for themselves.
Ask them how plants differ from animals. They will say that plants are
fixed to one place, while animals can move about; that plants have no will
or consciousness, and that animals have. These answers are true when we
compare the higher animals with plants, but the differences become lost as
we descend in the scale and approach the border land where botanist and
zoologist meet on a common ground. Sea-anemones are fixed to the rock on
which they grow, while some of the lower plants are able to move from
place to place, and it is hardly safe to affirm that a jelly-fish is more
conscious of its actions than is a Sensitive Plant, the leaves of which
close when the stem is touched.
There is no real division between animals and plants. We try to classify
the objects about us into groups, according to the closeness of their
relationships, but we must always remember that these hard lines are ours,
not Nature's. We attempt, for purposes of our own convenience, to divide a
whole, which is so bound together that it cannot be separated into parts
that we can confidently place on different sides of a dividing line.
1. _Plants as Food-Producers_.--The chief distinguishing characteristic of
plants is one that the pupils may be led to think out for themselves by
asking them what animals feed upon. To help them with this, ask them what
they had for breakfast. Oatmeal is mentioned, perhaps. This is made from
oats, which is a plant. Coffee and tea, bread made from wheat, potatoes,
etc., all come from plants.[1] Beef, butter and milk come from the cow,
but the cow lives upon grass. The plant, on the other hand, is nourished
upon mineral or inorganic matter. It can make its own food from the soil
and the air, while animals can only live upon that which is made for
them by plants. These are thus the link between the mineral and animal
kingdoms. Ask the scholars if they can think of anything to eat or drink
that does not come from a plant. With a little help they will think of
salt and water. These could not support life. So we see that animals
receive all their food through the vegetable kingdom. One great use of
plants is that they are _food-producers_.
[Footnote 1: Reader in Botany, for use in Schools. Selected and adapted
from well-known authors. Ginn & Co., Boston, New York and Chicago, 1889.
I. Origin of Cultivated Plants.]
This lesson may be followed by a talk on food and the various plants used
for food.[2]
[Footnote 2: The Flour Mills of Minneapolis: Century Magazine, May, 1886.
Maize: Popular Science News, Nov. and Dec., 1888.]
2. _Clothing_.--Plants are used for clothing. Of the four great clothing
materials, cotton, linen, silk, and woollen, the first two are of
vegetable, the last two of animal origin. Cotton is made from the hairs of
the seed of the cotton plant.[1] Linen is made of the inner fibre of
the bark of the flax plant. It has been cultivated from the earliest
historical times.
[Footnote 1: Reader in Botany. II. The Cotton Plant.]
3. _Purification of the Air_.--The following questions and experiments are
intended to show the pupils, first, that we live in an atmosphere, the
presence of which is necessary to support life and combustion (1) and (2);
secondly, that this atmosphere is deprived of its power to support life
and combustion by the actions of combustion (2), and of respiration (3);
thirdly, that this power is restored to the air by the action of plants
(4).
We have the air about us everywhere. A so-called empty vessel is one
where the contents are invisible. The following experiment is a good
illustration of this.
(1) Wrap the throat of a glass funnel with moistened cloth or paper so
that it will fit tightly into the neck of a bottle, and fill the funnel
with water. If the space between the funnel and the bottle is air-tight,
the water will not flow into the bottle.
[Illustration: FIG. 1.]
Do not explain this in advance to the pupils. Ask them what prevents
the water from flowing into the bottle. If they are puzzled, loosen the
funnel, and show them that the water will now flow in. In the first case,
as the air could not escape, the water could not flow in; in the second,
the air was displaced by the heavier water.
Ask the pupils why the air in a crowded room becomes so difficult to
breathe. Could a person live if he were shut up in an air-tight room for a
long time? Fresh air is necessary to life. The teacher may explain that it
is the oxygen in the air that supports life. Air is composed one-fifth of
this gas and four-fifths of nitrogen. The gases are mixed and the nitrogen
simply dilutes the oxygen, as it were.
Fresh air is necessary to support combustion as well as life. Ask them why
we put out a fire by throwing a blanket or a rug over it. The following
experiment illustrates this.
(2) Take a small, wide-mouthed bottle, covered with a card or cork. To
this cover fasten a piece of bent wire with a taper on the end. Light the
taper and lower it into the jar. It will burn a few seconds and then go
out. Raise and light it again, and it will be extinguished as soon as it
is plunged into the bottle. This shows that the oxygen of the air is used
up by burning substances, as it is by breathing animals.
[Illustration: FIG. 2.]
The following experiment shows that fire will not burn in an atmosphere of
gas from our lungs.
(3) Fill a bottle with gas by breathing into it through a bit of glass
tubing, passed through a card or cork, and reaching to the bottom of the
bottle. The bottle will be dimmed with moisture, showing the presence of
aqueous vapor. A lighted match plunged into the bottle will be immediately
extinguished. A better way, which, however, takes some skill in
manipulation, is to fill the bottle with water, cover it with a flat piece
of glass, and invert the bottle in a dish of water, taking care that no
air bubbles enter. Then, through a bit of glass tubing, blow into the
bottle till the water is expelled. Cover the mouth with the glass under
water, and holding it tightly down, invert the bottle quickly. Set it
down, light a match, take away the glass, and at the same instant plunge
in the match. If no air has been allowed to enter, the match will go out
at once. No animal could live in an atmosphere which could not support
combustion.
From these experiments the pupils have seen that the life-sustaining
quality of the air is used up by combustion and respiration. To bring in
the subject of purification by plants, ask them why all the oxygen in
the world is not exhausted by the people and the fires in it. After the
subject has been explained, the following experiment can be prepared and
put aside till the next lesson.
(4) Fill two bottles with air from the lungs, as in (3) having previously
introduced a cutting from a plant into one of the bottles. Allow them to
stand in the sun for a day or two. Then test both bottles with a burning
match. If properly done, the result will be very striking. The end of
the cutting should be in the water of the dish. This experiment will not
succeed excepting with bottles such as are used for chemicals, which have
their mouths carefully ground. Common bottles allow the air to enter
between the bottle and the glass.[1]
[Footnote 1: See note on page 13.]
[Illustration: FIG. 3.]
4. _Fuel_.--Light a match and allow it to burn until half charred. Blow it
out gently, so as to leave a glowing spark. When this spark goes out it
will leave behind a light, gray ash. We have to consider the flame, the
charred substance, and the ash.
Flame is burning gas. In all ordinary fuels, carbon and hydrogen, in
various combinations and free, make the principal part. The first effect
of the heat is to set free the volatile compounds of carbon and hydrogen.
The hydrogen then begins to unite with the oxygen of the air, forming
water, setting free the carbon, which also unites with oxygen, forming
carbonic acid gas. The burning gases cause the flame. The following
experiment will illustrate this.
[Illustration: Fig. 4.]
(5) Fit a test-tube with a tight cork, through which a bit of glass
tubing, drawn out into a jet, is passed, the tubing within being even with
the cork. Place some bits of shaving in the tube, cork it, and make the
cork perfectly air-tight by coating it with bees wax or paraffine. Heat
the test-tube gently over an alcohol lamp. The wood turns black, and vapor
issues from the jet, which may be lighted (Fig. 4). Care should be taken
to expel all the air before lighting.
(6) That the burning hydrogen forms water by uniting with the oxygen of
the air, may be shown by holding a cold glass tumbler over the jet, or
over any flame. The glass will be dimmed by drops of moisture.
The charred part of the wood is charcoal, which is one form of carbon.
Our ordinary charcoal is made by driving off all the gases from wood, by
burning it under cover where only a little air can reach it. The volatile
gases burn more readily than the carbon, and are the first substances to
be driven off, so that the carbon is left behind nearly pure. In the same
way we have driven off all the gases from the half-burned match and left
the carbon. The teacher should have a piece of charcoal to show the
pupils. It still retains all the markings of the wood.
If the combustion is continued, the carbon also unites with the oxygen of
the air, till it is all converted into carbonic acid gas. This was the
case with the match where we left the glowing spark. The gray ash that was
left behind is the mineral matter contained in the wood.
(7) We can show that this gas is formed by pouring lime water into a
bottle in which a candle has been burned as in (2). The water becomes
milky from a fine white powder formed by the union of the carbonic acid
gas with the lime, forming carbonate of lime. This is a chemical test.
The wood of the match is plainly of vegetable origin; so also is the
charcoal, which is nearly pure carbon. Coal is also carbon, the remains of
ancient forests, from which the gases have been slowly driven off by heat
and pressure. All the common fuels are composed principally of carbon and
hydrogen. When these elements unite with oxygen, carbonic acid gas and
water are formed.[1]
[Footnote 1: [Transcriber's Note: This note is missing from original
text.]]
(8) The same products are formed by respiration. We breathe out carbonic
acid gas and water from our lungs. Breathe on a cold glass. It is bedewed
exactly as it is by the candle flame. Breathe through a bit of glass
tubing into a bottle of lime water. It becomes milky, showing the presence
of carbonic acid gas. Why is this?
Every act or thought is accompanied by a consumption of material in the
body, which thus becomes unfit for further use. These waste substances,
composed chiefly of carbon and hydrogen, unite with oxygen breathed in
from the air, forming carbonic acid gas and water, which are breathed
out of the system. The action is a process of slow combustion, and it is
principally by the heat thus evolved that the body is kept warm. As we are
thus constantly taking oxygen from the air, a close room becomes unfit to
live in and a supply of fresh air is indispensable. The cycle of changes
is completed by the action of plants, which take in carbonic acid gas, use
the carbon, and return most of the oxygen to the atmosphere.