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How Does a Tree Grow? online

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_Sub-Inspector of Denominational Schools, Victoria,
Author of “Geography of Australia and New Zealand,”
&c. &c._




At the request of several Teachers, I have commenced a Shilling Series
of School Books, chiefly to be confined to subjects of Colonial History
and Popular Sciences.

The form of dialogue has been adopted with the “Botany for Young
Australians,” from a belief that the sympathies of our young friends
will be excited on behalf of the juvenile questioner, and their
interest thus maintained in the study of the sciences.

A dialogue upon Astronomy will shortly follow; being a conversation
between a father and his son, coming out to Australia, from Old England.


_Melbourne, April 17, 1857._


Willie was a fine rosy-faced boy of our southern colony. Though not
eight years of age, he was as healthy and merry a lad as ever climbed
up a Gum tree, picked up manna, or rode in a bullock dray.

His father had once occupied a good position in Old England; but
the uncertainties and losses of business, and the constant struggle
to uphold a respectable appearance with decreasing means, became so
burdensome to his mind, that his spirits failed, and his energies sunk.
His attention was directed to Australia, the land of mutton and corn,
the home of health and plenty. Gathering up the wreck of the past, he
left the country of taxation and paupers, and established himself on a
small farm in Port Phillip.

The young hero of our story had been a year or two in the colony. It
so happened he had a piece of land of his own, in which he proudly
exhibited some rising cabbages, a few peas, and a flower or two. His
father had given him a rose tree, which was the reigning beauty of the
bed. It was upon the occasion of his parent’s visit to the garden, that
the following dialogue took place: -

Look, father, and see how my rose tree has grown.

Indeed it has, Willie. Can you tell me what has made it grow?

The sun and the rain, I suppose.

Do you remember, when we got tired of the old slab hut, and set about
building this brick cottage, that you noticed it getting higher and
higher every day!

Yes, that was because more bricks and wood were used.

Then, if your tree increases in size, there surely must be something
added on continually: do you think the sun and rain do this?

Well, I never thought about it, father; but I should like to know why
it does grow.

Can you tell me, Willie, what a plum pudding is made of?

Yes, that I can. There is the flour, the suet, the raisins, and the
cold water. All these are mixed together.

Then let us see of what our rose tree is made.

I don’t think it so easy to tell that as to reckon up the articles in a

Never mind, we will try. First, there is the stalk, or woody part.
When you put a piece of stick in the fire, what becomes of it?

Oh, it smokes and blazes, and then nothing is left but some ashes.

What is it which burns away?

That I cannot tell.

It is the gaseous part which burns in a flame, like what you have seen
come out of coal. But what do you call woody matter that will not blaze?

Charcoal, father. Then I understand now that wood is nothing but
charcoal and the gases. What are these gases?

The gas which blazes so readily, my dear, is hydrogen: and it has
a very strong smell too. The air we breathe is a mixture of two
gases - oxygen and nitrogen. It is only the oxygen that we take into our

Well, that is curious.

I shall puzzle you more, Willie, when I tell you that water is nothing
but a mixture of oxygen gas and hydrogen gas.

It certainly is funny that water, which puts out flame, should be
partly composed of the burning gas.

You must also know, my lad, that hydrogen would not burn without
oxygen. You blow air into a fire to give food for flame.

But however could the plants get hold of the gases, father?

Did it never strike you why God formed leaves?

It never did, except that I thought he did it to make the trees look

That is quite true, Willie. The good God loves beauty, and he has
surrounded us with beauty of all kinds. But he made things for use as
well as to be looked at. The leaves absorb or suck in gases from air
and water.

Then I suppose the veins like that we see in leaves conduct these gases
away into the plant.

Quite right, my boy. Where now shall we get the charcoal, or carbon, as
the learned men call it?

That I cannot find out at all.

You told me, Willie, that smoke came out of burning wood. What becomes
of it?

When I was a very little boy, I thought it went up to form clouds; but
now I know part of it turns into soot in the chimney, and that looks
like our charcoal or carbon.

It really is. As to that which comes out of the chimney, it passes
upward, and gets gradually mixed with the air. The little particles of
carbon join the oxygen, and become a sort of gas called carbonic acid
gas, which is absorbed into the plant.

How wonderful that the solid part of a tree should once have been
floating about in the air!

Do you think the leaves of a plant to be the same as the stem?

Yes, I do; for when they are thrown in a fire, they smoke, blaze, and
leave an ash like the wood does.

Just so. You know the smoke to be carbon passing into the air; but we
must examine the ash a little more carefully. If you take some ash from
the fireplace, and put it into hot water, the solid part will of course
fall to the bottom.

Will no part mix with the water?

There will be something; for if we pour off the water, and allow it to
evaporate in a dish, there will be found to be a sediment left, and
that is potash or pearl ash.

I have heard of people in the bush doing that when they could not get
soap, for they said that the potash got the dirt out of clothes.

It is a great pity that we in these colonies burn away so much wood in
waste when clearing land, Willie, without thinking of making potash out
of the ashes, for it fetches a good price.

Then there is potash in the plant. Has any thing else been found in the
ash beside that and carbon?

Yes, my lad. Sulphur or brimstone, lime, soda, flint, ammonia,
phosphorus, magnesia, and iron, are contained in trees.

But how could all these things get there?

Why, if we cannot find them in the air to be absorbed by the leaves,
they must be in the soil or ground. Now, it so happens that those
substances are to be found in different quantities in different places.

How do they get into the plant, father?

Simply by the little rootlets absorbing small particles of them, mixed
with moisture.

But do all plants require the same amount of lime, potash, soda, and
the others?

No, my dear. There are not two sorts of trees that feed upon the same
materials in exactly the same proportions.

Is that the reason, then, why some land is so much better fitted to
grow one plant than another?

The reason is, because the one soil has more of the right sort of food
in it.

Now I see that if I wanted to grow a good crop of any thing, I must
give it plenty of the food it likes best.

Yes, but not too much. For like as too much nice rich food is bad for
children, so it is with vegetables: ground may be too rich, as well as
too poor.

I have heard people say that it is not wise to grow the same thing in
the same soil year after year: why is this?

Because it would gradually consume all the food there, and then it
would starve, and look miserable.

Then my beautiful flower-bed will by-and-by cease to bring forth such a
fine show as it has done this season.

Of course it will, unless you provide your plants with fresh food.

Fresh food, father; I do not understand you.

I mean, manure must be mixed with the soil.

How is manure food for plants?

Because it contains the materials they require. You throw wood ashes
over the ground, and so add sulphur, potash, and carbon. Sea weed
manure furnishes plenty of soda. Bone dust contains lime and phosphorus.

It is possible, then, to apply to the ground the amount of solid matter
taken out of it by the plant, so that if my radish bed had some manure,
it would be as good as it was before my crop came off.

That is perfectly correct, my boy.

But how is it that a gum-tree forest is kept up, for there must be a
tremendous lot of lime, soda, flint, and the rest, removed from the

Yes, but when the trees fall, they rot, and the solid parts return to
the ground.

Oh, father, the remains are very small, compared to the living tree.

True, because the principal part of a plant consists of the gases,
which fly off, and of carbon, which unites with the oxygen of the air.

How does God bring fresh carbon to the forest?

Several ways: smoke is one source, and the breath of animals another.

What has the breath to do with it?

Every time you respire, or breathe out, some carbonic acid comes out
with air, and is carried into the atmosphere.

Why, father, you do not mean to say that my breath helps to make
cabbages grow.

The carbon passing from your body may become a part of a cabbage, or
gum tree, or a delicate tulip.

* * * * *

The next time Willie and his father were out together, the conversation
again fell upon trees. The wonder of the boy had been strongly excited
by the last lesson, and he had now lots of questions to ask. He knew
enough to know that there must be a great deal more to learn. He had
been told that trees fed the same as animals, and he felt sure that
inside there must be some entrances for the food to reach parts needing
supply. Then he sought to understand how the growing process was
managed, and especially how seeds were formed, and how the plant sprang
from them. Thus, question after question poured out from the boy’s
lips, without even a pause for a reply.

“Stop, stop, my man,” said his father; “I am not like the Hindoo
god with half-a-dozen pairs of ears, and half-a-dozen tongues. We will
go now a little deeper into the subject; but we must take one thing at
a time. What do you think of that gum tree yonder?

That is a noble fellow. What a barrel he has got for splitting paling
out of! And hasn’t he got a fine top knot? Why, that must be almost as
big as that Tasmanian tree you read about.

Oh, no; that one was 350 feet high, and was 104 feet round; while this
is not above 100 feet high, and 30 round.

Well, then, that must be a monster surely. How curious to think it was
once a tiny little thing that I could pull up with my finger! I say,
father, how many cartloads of carbon this one must have got hold of! I
fancy it has got gas enough to fill many a balloon. But how did it grow?

To answer that question, will give us some trouble, and take some time.
First, tell me all the parts of the tree.

What I cannot see is the root; then comes the stem, then the branches,
and then the leaves.

You forget the flower.

Flower! whoever heard tell of a gum flower? How funny the word sounds!

If there be no flower, how are you to get the seed?

I never thought of that. But flowers are always such pretty light
things, that one would be sure to see them a long way off on a gum tree.

But if instead of having fine red leaves, my lad, the flower had none,
and the other part was much the same colour as the leaves, do you think
you would notice it so readily?

No, father. Won’t I give a good look out for it after this; for I am
sure none of our boys at school ever talk of gum flowers, though we
often go to gather wattle blossoms.

To go on with our tree - we will take the root, and there is a Stringy
Bark blown over in the last storm.

And a strong root it has, too. How the wind must have puffed to
overcome the weight of all the gravel and clay resting on that lot of
roots, especially as they held the gravel like so many fingers. So
these are the suckers of moisture and food out of the soil.

Yes, but you do not see the real suckers. They are very small, and were
broken off and left behind. Those are called _spongioles_, because
they suck up like a sponge. They are situated at the ends of the small
fibres of roots, and have their mouths always open.

Yet I don’t see why the moisture rises. If I put my mouth into the rain
cask, the water will not rush up into it.

Your mouth is too big. Supposing you put a lump of salt near a little
water, so as to be touched, what will be the result?

The salt will gradually absorb the water, until there be none left.

After dipping the corner of a towel in the basin, and hanging it up by
the opposite corner, does not the dampness run down when drying?

No, the moisture ascends and wets the dry part of the towel.

So you see, then, that the water in small particles can arise in the
pores, or narrow openings of substances. This is because the sides
attract it, and the process is called _capillary_, or hairlike,
_attraction_. On this principle the moisture rises into the rootlets
through the spongioles.

Is that all the work they do?

Sometimes these fibres reject things not wanted in the tree, and that
often prove poisonous to its growth. Such important little workmen as
the spongioles ought not to be disturbed in their labour, and this is
what makes the difficulty in moving trees.

I know that most of those I move are sure to die. But gardeners are
more lucky.

The reason is, because they do it at a proper time.

What, father, can we catch the spongioles asleep?

Not exactly; but they only live a year, and you must take up the
tree between the time of the death of one set, and the production of
another, which is the winter season. Even then you should get up as
many fine roots as possible, for at the end of these the spongioles

All roots are not alike, father.

That is true: some are creeping, or fibrous, or bulbous, or knobbed, or
taprooted. Can you give me instances of each?

Let me see. The mint spreads underground by its creeping roots. The
potatoe is knobbed, and the onion and tulip are bulbous. The grass is
fibrous, and the parsnip has a tap root.”

* * * * *

So much for the root. Now let us look at the bark. I suppose you have
noticed the difference of the bark of our forest trees.

I know that they shed their bark, though not in the same way. The
stringy bark peels off in strings. The gum throws out fine long
ribands, waving in the wind. The iron bark sheds its thick coat in
great lumps.

But does the whole of the bark thus fall off?

Oh, no: it is only the rough, worn-out stuff. There is always bark
left. It puts me in mind of _my_ hand, that got so horny after sawing a
whole day at a big tree; for days after the rough skin got peeling off
as if it was not wanted.

Then you have more skins than one. You are just like a tree, for that
has several coats to its bark. Which is the softer, the outer or inner

The outer is hard, and the inner soft. But there is a fresh gum tree
just cut down: that will show us the barks. - Yes, now I peel off the
outside, there is a very soft, juicy stuff, a thing I feel - a soft coat
of bark close to the ring of white-looking wood.

Mind, Willie, the outside is the _cuticle_ or _epidermis_, having
pores or openings through which moisture issues at one time, and is
absorbed at another. These _Stomates_ or openings are very small; in
our Bush Pigfaces, that the Blacks eat, there are 70,000 Stomates to
every square inch of skin.

Then the tree perspires in the same manner that we do: that is odd. But
what is the middle pulpy bark, with its green colour and sticky feeling?

Botanists call that the _Chlorophyll_ or colouring matter. The inner
bark is the _liber_, which you see to be soft and fibrous like, being
full of sap.

Why, this is something like our skin, as there is a watery stuff
between our cuticle and the skin that has the blood in it. I have heard
of people writing on bark: that must have been on the liber.

It was so. The English wrote on the bok or bark, and thus we have the
word _book_; while with _liber_ we connect the word _library_. But we
shall return to the liber in another lesson.

Is the cuticle always naked?

No, some plants I have seen with hair over the skin, and others with
something like scales.

* * * * *

Having talked of the bark, boy, we will turn to the stem. What are your
notions about it?

My eyes and fingers tell me that, after I pass the liber of the bark,
I reach the fresh-looking white ring of wood, and that after that the
wood which is still in rings gets harder and drier toward the centre.
But I thought there was pith in the middle of a tree: how is it there
is none seen here?

Because these woody layers or rings have crushed it in time. I must say
a little about this pith. You know it is soft enough; that is, because
it is composed of small cells filled with juices at first, and then
with air.

Cells, father! what, like the bees’ honey-comb!

Yes, indeed, and six-sided like those cells. The walls, however, are
not made of wax, but of _cellular tissue_. This tissue is a fine
membrane, or skin; or, rather, a transparent, colourless, film. Mucous
threads connect the cells.

What curious things to be in a tree?

I shall astonish you more when I tell you that all your tree - root,
bark, pith, wood, and leaf - every one of these is composed of a number
of these little cells. Do you see those small spots in the wood, and
these in this leaf in my hand?

I do, father.

They are thought to be the openings of the cells, through which various
juices may pass. Some cells are round and regular, as in the leaf;
while those of the wood, from being much crushed, are spindle shaped,
like a tap root.

Would they not be round in the fruit, then?

They would, Willie, and are there filled with some nice secretions,
that boys rather enjoy. In the pretty leaves of flower, they contain
a coloured fluid. Some cells hold carbon, and others have crystals of
flint, lime, iron, starch, &c. Sugar, gum, resins, turpentine, &c., are
in cells.

That is where the scratching stuff comes from, which I have felt in the
cutting grass and wheat straw. But are there cells in roots?

Yes. There are, also, long tubes in plants like our water pipes, which
are open at each end, not closed like the cells. They are parallel
to the line of the stem, and are extremely small. They may be called
elongated or lengthened cells, and form what is called the _vascular
system_, or system of vessels.

Is there any other sort of vessels?

Some are _spiral_, or twisted. The _tracheae_ are such. Some are round
the pith. It is supposed that these convey air from one part to another.

Are these spirals everywhere?

No, there are none in the bark nor root - nor have ferns any. Speaking
of air tubes, I may tell you that aquatic or water plants have air
cells divided from other parts by layers of cellular tissue.

What do the spirals want with air?

You have been told that oxygen of the air is as necessary to the life
and nourishment of a tree as of a boy; sometimes the leaves do not
absorb enough, and then the spirals get it, through the root, from the
moistened soil.

I can now understand why so large a thing as a tree becomes so small
when the really solid part is got together. If all the cells and
vessels were jammed up tight, so that the air and juices were driven
out, how thin our thirty-feet round gum tree would appear! But will you
tell me if the regular sap runs through those vessels we have talked of?

It is considered that it runs rather between the interstices or
openings between the cells.

Why do you say _considered_ and _supposed_?

Simply because the things we talk of are so very minute or small that
the most powerful microscope will scarcely exhibit them, and thus it is
difficult to observe their nature and action.

* * * * *

Father, what are these silver lines through the solid wood, coming from
the pith centre?

They are the _medullary_ or _pith rays_, and reach the liber or
inner bark. They convey nourishment. Through them there is also a
communication between the root and the leaf.

I want to ask a question about the leaf. Does it throw off anything as
well as absorb?

You have been told that it absorbs oxygen from the air, and also
carbonic acid gas - that is, carbon and oxygen. This carbonic acid
floating in the air is absorbed in the day-time, though the leaf
exhales, or breathes out, oxygen gas while the sun shines.

_Does it not do so at night?_

No; then the leaf throws out some carbonic acid gas undigested. There
is this use of the oxygen being taken in by the leaf, that it acts
beneficially upon the sap to thicken it, &c.

What is the true shape of the leaf?

The course of veins or branching vessels. The fleshy part of the leaf
is of cellular tissue.

I have heard that our leaves differ from English ones: how are they
different? I know they do not fall off in autumn.

English leaves are made to fall, as from the first they are nearly
divided from the _petiole_ or leaf stalk, the mark of division being to
be seen in the budding leaf.

Have our Australian leaves that mark?

No, they have not. The petiole expands or becomes leafy, and the
leaves, therefore, do not readily fall. There is yet another
difference. While the glands or tumours for imbibing moisture are on
the underside of the leaf in England, they are on both sides of it
here. Instead, too, of being horizontal, our leaves are set in edgewise
on their stems.

I often notice the great difference there is in leaves, father.

Yes, they differ in size, structure, direction of veins, situation,
form, duration, kind of surface, &c.

But what have you to say of those plants which have no leaves? I could
never see any in our sheoak nor cherry.

Quite true. Our _Casuarina_ or oak family, and the _Exocarpus_, or
cherry, have no leaves. They have, however, long hanging knotted twigs
at the end of branches. They have been called the Pines of Australia.

Is light necessary to leaves as well as air?

It is. Sunlight acts chemically to produce changes in substances. It is
believed necessary to enable the leaf to separate the carbon from the
oxygen in carbonic acid gas. Leaves love light, and will turn toward
it. Some even follow the sun in its daily motion. In a dark place,
plants soon fade, and the leaf turns white.

* * * * *

Well, father, we have got rid of the root of our gum tree, as well as
its bark and leaves - what shall we take next? I seem to know a good
deal, but I cannot yet make out how the tree grows.

But you are prepared now to understand that part of my lesson to come.
You see the rings of wood, and the rings of bark, and you want to know
how they come there.

Yes, that I do. Of course I could say that the sap makes wood, as I
know that bread and butter make flesh; but I want to understand how the
change takes place.

Let us then imagine ourselves, Willie, to be spirits able to be inside
of the tree, without taking up any room, and with our eyes about us to
watch all that is done.

I wish I could do that; it would be better than flying.

Don’t talk about it, but jump inside along with me.

I am with you, father, with eyes and ears all open.

I’ll tell you what it is, Willie, we shall have not only to be inside
the tree, but to be able to stay there a few weeks or months to notice

That is easy enough. We may as well fancy hundreds of years as millions
of miles.

Let us go to the pith. Around here are vessels in the sheath of the
pith. The circles of wood are ranged outside. We will pass along one of
the Medullary or pith rays, which you saw make the silver lines of the
wood, and here we are at the Liber or inner bark.

But what is this soft white wood next to it?

This is the _Alburnum_, or white wood. When you tap a tree, the sap
comes from this part. Now watch what is coming.

I see - the Liber is separating from the soft Alburnum, and there comes

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