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How Does a Tree Grow? online

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a sticking substance of sap oozing between them. What is that?

It is the _Cambium_, or _Albumen_; the white of egg is albumen. Look
again.

Ah! the cambium is softening the cellular tissue that bound the liber
to the alburnum, and while that is growing outward, I find that the
other parts are growing upward.

Let us take a peep at the leaf buds. You see they feel the growing
influence, and are letting fall bundles of woody matter, which pass
into the cambium, and become attached to the liber. The cellular
tissue passes in the mass around, along the medullary rays, and a new
substance becomes attached to the liber.

But that new substance is another alburnum, father, and our old
alburnum is turned a quite hard wood.

You see, then, that while the last year’s soft wood becomes a hard ring
or layer, another is formed in its place alongside of the liber. The
hard wood is dead compared with the softer kind.

I think I understand that. But where does the nourishment come from?

The sap when first rising is watery and nearly colourless. But after
exposure to air and light in the leaf, and losing much water in
evaporation, it becomes thicker, and, descending by the bark, is
prepared, like blood, to renew and to form different parts of the
structure.

Is there any other movement of the fluids of a plant?

Yes, there is a true circulation in the interior of all the cells.

Does a tree form a fresh ring of wood every year?

This depends upon the character of the tree. Some trees take many years
in forming it.

How is it that the layers of our Gum tree are not equal in thickness?

That is influenced by the season. One year it was very cold or dry, and
the tree made little wood. Another season, the rain was abundant, and
the sun did his work well, and so the _concentric_ or ring-like layer
was fuller.

But I see that on one side of the tree, the bands are thinner than on
the other.

That was the side that received the cold wind. The greater the number
of leaf-buds above a part of a stem, the greater the diameter.

How does the bark manage when the tree forms new wood, and presses
against the liber?

The outer bark cracks and peels off. When the bark grows, it does so
internally; a new liber appearing adjoining the layer of new alburnum.

What connection, father, has grafting trees with growing?

The gardener takes a bud of one fruit-tree, and applies its liber,
the life part, to the liber of the stock of another tree, binds them
together, and puts clay outside to exclude the air. The nature, then,
of the bud is communicated to the tree; the juices will be altered, and
another fruit produced.

Well, thank you kindly, dear father. I do feel that I know something
now about a tree growing. I can tell, too, why a tree does better in
one place than another, making more wood and leaves. It is when it
can find in the soil a sufficient amount of food, in the carbon, lime,
phosphorus, sulphur, potash, and the like.

Quite right, and some other day we may have a talk about the varieties
of manures, and the way of tilling the soil, especially in relation to
Australian farming. But it is now time for us to return home. So come
along, my boy.

* * * * *

It was not until a few days had passed, that Willie’s father was at
leisure to give another lesson. During that interval the boy had
not been idle. He had roamed over the Bush, and stored up lots of
specimens of the vegetable world. There were many varieties of roots
in one place, and of bark in another. He had cut open many a plant
to try to observe some of the peculiarities of which his father had
told him. The leaves being so perishable, rather bothered him in his
researches, till his mother showed him how to preserve them, by placing
them between sheets of blotting or other soft paper, and changing the
wrapper occasionally. Willie himself was astonished at his collection,
and greatly surprised at the many kinds of leaves he had obtained.
Having some notion of drawing, he set about copying a few of the most
curious forms, especially in cases where he thought the pressure would
spoil the appearance. His good father, as you may be sure, was quite
delighted at his son’s industrious research.

One thought had all this while very much perplexed our young friend. He
had a fair notion of the causes of the growth of a tree after it had
begun to grow; that which puzzled him was, how the tree arose from a
seed, and how the seed itself was produced. He unburdened his mind to
his father.

To describe this subject, said the father, I must give you the history
of a flower.

I used to think, father, that the flowers were only formed to please
our eyes, and yet I knew the seeds had something or other to do with
them.

You are partly right. There was no reason for flowers to be pretty,
any more than for butterflies. But it has pleased God to put the
beautiful along with the useful. He has thus adorned this world for our
home, that his creatures may be the happier in it. You have doubtless
observed that flowers are as various as leaves.

I have done so, and I remarked that the same sort of plant always
produced the same kind of blossom, year after year, just as birds lay
certain eggs of their own sort only. How is this?

No one can answer that question, except by saying that God has
established fixed laws, according to which everything acts in order.
The planets turn round the sun, the sun appears every morning; plants
and animals produce their like, and everything that God has made moves
in its proper path.

Except men and women, father. And yet I think if stars and flowers know
and do their duty, we should be at least as good as they.

Now for the flowers, Willie. What do you see in them?

There are the pretty leaves, the common-looking green leaves outside of
them, and a lot of things standing upright in the middle of the flower.

Your pretty leaves are the _Corolla_ of the flower; the green ones form
the _Calyx_; and the standards inside are _Stamens_ and _Pistils_. We
will take one at a time, and begin with the Calyx, although that, and
the Corolla too, may be wanting in a plant, as they are not really
necessary.

It seems as though the Corolla took care of the Stamens, and the Calyx
protected the Corolla.

You are not far from the mark, my boy. But can you tell me whether the
Corolla of a flower is always in one piece or not?

I should think not. I recollect some flowers with one pretty cup all
round, while others are made up of a great many coloured leaves.

You must call those leaves _Petals_. Some plants have four petals in
the form of a cross. Did you ever notice a pea blossom?

Yes, father, and thought it a funny one.

Just gather one and examine it. How many petals are there, and how are
they placed?

There are five, but not all of the same size. There is a good upper
one, two side ones, and two at the bottom, enclosing the rest of the
flower.

That upper one is the standard, and the two at the sides are the wings.
Could you describe the orchis, the wild flower of our bush?

I will try. There are six petals; three are bent backward, two are at
the sides, and one opposite to the three is also bent backward. Is not
honey found at the bottom of the corolla cup?

It is, in a place called the _Nectary_. I shall afterwards explain the
object of the sweets. But we must hasten on to the _Stamens_. These
generally arise from near the base of the petals.

Are they the ones with the yellow dust on the top?

They are, my lad. If you look at one, you will find a long thread or
_Filament_, bearing a loose top, called the _Anther_, which carries the
_Pollen_ or yellow dust.

But why is not the pollen always to be felt on the anther?

Because it is shut up in cells at first. When the walls of these burst
open, the pollen shows itself outside, and is also scattered about.

As things alter so strangely under the microscope, father, how would
our dust look there?

No two plants have the same shaped pollen, which is of all possible
forms. The tiny grains are generally each enclosed in a delicate bag,
the subtle powder of which is more like smoke than anything else, in
which are particles of starch or drops of oil.

But our orchis does not seem to have a regular anther, for the pollen
looks all of a heap.

That is correct. But which do you fancy is the _Pistil_?

I don’t know, unless it be that in the middle surrounded by the
stamens. This is a thread, too, with a knob at the top.

The support is the _Style_, and the summit is the _Stigma_. When you
examine flowers you will observe the stigma of various shapes and
sizes; but there is always a sticky substance on the top. Does the
pistil rise from the same place as the stamens?

No, it comes from a lump at the bottom.

That lump is the _Ovary_, or seed basket, sometimes known as the
_Germen_. Some botanists believe that the several parts of flowers are
only metamorphosed, or changed leaves, and that the pistil is one of
these growing vertically. You have seen in a double stock, or other
double flower, that the stamens have grown into petals.

But why is it that the corolla falls off so soon? I have seen our
garden beds strewn with blossoms, and yet the stamens and pistils keep
on much longer.

But what happens when these go in their turn, Willie?

Why, the ovary, as you call it, swells out. But what makes the fruit?

That fleshy substance around the seeds, of which you are so fond,
is merely the swollen _Pericarp_, or covering of the seed vessel.
Children’s teeth should not go into the pericarp until the seeds are
about ripe.

I know that. When a pear is nice and mellow, then the seeds within are
quite hard. But would you call the pod of the pea a pericarp?

Certainly. It consists of two valves, with hinges, and the seed on each
side. Sometimes there are several valves together, and we call the
whole a _Capsule_. When these burst, the seeds fall out.

But how are the seeds produced?

We are coming to that next. I told you of the bursting of the anther,
and the scattering of the pollen. Though much of the dust is wasted, a
part is caught on the glutinous stigma of the pistil.

And what becomes of it then?

It passes down the hollow style into the ovary at the bottom.

Yet I have seen flowers in which the pistil was higher than the
stamens; how could the pollen reach it?

Many curious contrivances effect the transfer. The wind blows the
yellow dust. A bird throws some about. An insect catches some on its
wings and legs, and stepping on the stigma, leaves pollen behind.

Is the honey in the nectary to tempt the insects to the flower?

The sweet morsel attracts birds as well as insects.

When, then, the stamens have discharged their pollen, and the pistil
conveyed it to the germen, I suppose there is no further use for them.

There is not, and they die off like the petals of the corolla and the
calyx before them. But because of the variety of stamens in number and
situation, botanists have thought it well to divide plants into classes
by this means.

How do they do that, father?

They place in one class all vegetable substances whose flowers contain
but one stamen; in another, those with two stamens; and so forth. The
number and arrangement of the pistils enable us to form plants into
orders; as, a flower may have four stamens, and one pistil, or four
stamens and two pistils, &c.

I suppose the stamens and pistils are always found together.

No, they are not: though Compound flowers are made up of sets of
flowers within the same calyx, we have plants in which the stamen,
or male flowers, are in one part, and the pistil, or female flowers,
on another portion of the tree. The former are barren flowers; the
latter, fertile or fruitful, as the seed vessel is only connected with
the female side.

I think the service of winds, insects, and birds, is more needful
than ever now. But I have seen people pick off flowers from melon and
cucumber plants, saying, that they were no good.

These were the male blossoms. But they who pluck off all the barren
blossoms before the pollen appears, can never expect to have fruit; for
the fertile blossoms are of no use without the others. But what would
you think of male flowers being all on one tree, while the female are
upon another at a distance?

I suppose that is to give the birds and insects more work than ever.
Please tell me a tree that has this curious plan.

The Palm is an instance. Where the trees grow in a cluster, as they
usually do, there is no difficulty. If very far apart, the male
blossoms, when ripe, are cut off, carried to the other tree, and the
pollen shaken over the pistil flowers.

That is singular. But how do water plants get on with the yellow dust?

Some of them rise to the surface to flower, and sink to seed. Those
that keep below are provided with a glutinous pollen, which cannot be
affected with the wet.

* * * * *

Well, father, I do think we are getting on bravely with our lesson. But
I would so like to peep into the germen or ovary, and see what goes on
there.

We will do so. I ought to have said, that before the pollen sheds, the
ovary has a lot of half formed seeds adhering to the _Placenta_ inside.
These _Ovules_, as they are called, are a sort of nucleus or kernel,
and are each placed between two sacs of open mouths.

What goes into those mouths?

Nothing goes in, but the pollen of the stamens comes down through them
out upon the ovule, and is received to its _Embryo_, or heart, through
a very small hole. Soon after the pollen has entered, the ovule becomes
perfected and vivified, or made full of life.

And is that the seed?

The ovules do then become seeds in their little cells, and are, in
their turn, shed out when ripe.

But do they turn into real seeds directly the pollen gets down?

By no means. Nourishment and time are necessary to growth and change.
I must explain further about the seed. Beneath the _integument_ or
covering of ordinary seeds, as a pea, what do you observe, Willie?

I have seen the two halves of the seed show themselves, when the skin
breaks, and the plant seems to grow from between them.

Your two halves are the _lobes_ or _cotyledons_ of the seed. These
fleshy substances enclose the _embryo_, from which the leaves and
roots proceed. The upper part, from which the leaves arise, is the
_Plumula_, or _little plume_, or feather. That from which the rootlet
proceeds is the _Radicle_, or root part: sometimes it is called the
_Rostellum_, or _little beak_.

Of what use are the cotyledons, father?

They supply nourishment to the central portion, which is to develop the
plumula and rostellum, and thus surround them. A sort of passage of
communication exists between them. There is, also, a neck between the
plumula and rostellum.

What is that scar upon the seed?

The point at which it was attached in its vessel.

Well, now I think I really do understand all the mysteries of tree
growing. Like as a young animal suckles its parent until strong enough
to manage other food, so does a young plant depend upon the cotyledon
for provision, until its rootlets are able to search the soil, and
leaflets absorb from the air.

I trust, my boy, that while you admire the order and adaptation, you
will acknowledge Him whose wisdom planned the whole, whose power
performed it, and whose goodness makes it serve the happiness of His
creatures.

* * * * *

A few days after the last conversation, Willie went with his father
into the Bush among the mountains. The way was long, and the track
was rough, but various things occurred to make the journey pleasant.
The Laughing Jackass gave the boy a merry greeting, a snake peeped at
him slyly among the long grass, and then brushed off quickly to its
hole. A Porcupine raised up its quills as he passed, and then trotted
off to the scrub. But the trees, - the trees! How tall they were! How
thick they were! With the help of their handkerchiefs, Willie and his
father measured the girth of some, and found them thirty, forty, and
even fifty feet round. Most of the Stringybark and Gum trees ran up
straight as a dart, fit to thrust into some monster ship for a mast.
Then the sweet-scented shrubs on every side, the green Myrtle, the
pyramidal and beautiful Sassafras, and many others, seized upon the
boy’s imagination, until he came to a place that made him stare, and
then caper about like a Black fellow at a corrobory. What could it be?

A break in the tangled brush underwood had given him a peep down into
a valley that seemed prettier than anything he had read of in a fairy
tale. There was no rough rock, but a floor of soft moss. The most
musical of rippling creeks trickled along the vale. No other sound was
heard, for the very birds seemed afraid to disturb with their joyous
notes the silence that dwelt there. There were no Gums, no Wattles,
rising from this moss bed. Instead of these, Willie saw a lot of very
odd looking trees. They were not very tall, for they rarely rose above
12 or 15 feet. The bark was unlike anything seen elsewhere. There
were no branches, but at the top of the straight stem were several
branch-like leaves, 8, 10, and 12 feet long, with such a graceful bend
towards the valley. At the top of the stem, rising up from the place
where the leaves sprang out, was a curious curling piece, with little
shoots. The valley was full of these wonderful vegetable festooned
pillars.

Oh! Father! father! cried the boy, what are those beautiful trees down
there? I never saw any like them before.

They are Fern trees, my lad. Walk over and look closely at them.

Willie trod upon the soft carpet, and thought it damp, as well as soft.
The air, too, was so close, and felt so cold and raw, that he lost half
his pleasure already. He could not help saying so to his father.

Ah, my boy, said he, you are not the first to find nice things having
something disagreeable about them when approaching nearer to them.
Remember, that while roses have thorns, pleasures will have their
drawbacks.

Yes, I know I am often very tired after a pretty ramble, and rather
queer after a pasty.

True enough; there is only one place where happiness brings neither
fatigue nor surfeit. But let us see what is the difference between one
of these Fern trees and one of your old companions, a Gum tree.

I can tell. One is like a tree with branches and so forth; but the
other is not. Then the bark is quite different. I can see that the
leaves of the Fern tree are like those of the common Fern, which is so
troublesome in our sandy land, only they are a great deal larger.

But there is a stranger difference still. Just take my axe and cut one
of them down.

I can soon do that. It is not nearly so thick as that Wattle I fetched
down the other day with not a dozen cuts.

Willie doffs his jacket, catches at the axe, and is at once dropping
it in double quick time upon the Fern stem. A dozen blows were given,
and another, and another, but the tree did not fall. Taking breath, and
wiping his forehead, Willie murmured out: -

Well this is tough! it beats my Wattle, hollow. I declare if the
axe don’t ring against it as if it were iron or glass. It is quite
different from one of our trees, for that is rather soft at the
outside, though it may get harder as we get towards the middle.

As I think you are more likely to blunt my axe, than cut down the tree,
you may put on your jacket, and we will inspect that fallen fern I
see yonder. Perhaps after you have looked at the inside, you will find
another wonder.

It was not long before our young Botanist uttered an exclamation of
joyful surprise.

I have found it out, said he. Only fancy, father, I was hammering away
at a mere shell, though it was a hard one. The tree is quite soft
inside, though like flint outside. It is the very opposite to every
tree I ever saw before in all my life.

No doubt it is; and it was to see it with your own eyes that I brought
you here to the Fern tree valley.

Thank you, dear father, you always like to give me a treat, and this
is a rare one, too. But I am sure that such a tree as this could never
grow like a vegetable Gum tree, that you were telling me all about.

Can you name any plants, Willie, of which the fern tree puts you in
mind?

I know of none, unless it be the Bamboo, for that is hard outside and
hollow within, and it seems, like this, to grow up straight about the
same thickness throughout.

There is another tree of this character which we have in Australia,
some kinds of which grow in other countries, producing dates, of which
boys are so fond.

Any one can guess that: - it is the Palm. But whence have we Palms,
father?

There are some in Gipps’ Land, at the foot of the Australian Alps;
other finer ones are at Illawarra, south of Sydney; but more northerly,
in the hotter parts, Palms are very common.

Is that one from which we get our Cabbage Tree Hats?

It is so. The head of the Cabbage Palm is so good tasting and
nourishing, that many trees were felled on purpose to get at this sort
of cabbage, especially in the early days of the New South Wales Colony.

Then Palms, and Bamboo, and Fern trees grow the same way, as their
stems look the same, and as they have neither branches nor solid
timber. But how do they grow, father? There is no new wood formed
outside the last ring, as in the Gum tree.

It so happens, my boy, that new layers are formed for a while, inside
instead of outside. Our new class of trees are, therefore, called
_Endogenous_, from their growing internally, in opposition to the
ordinary forest trees, which are _Exogenous_, from growing externally.

I suppose the new shoots arise from where we see the joints in the
cane; but where is the fruit of our new Endogenous friend?

Have you never seen the pictures of bunches of dates and other fruits
all among the leafy branches at the top?

Eh! that I have, with the figures of Blacks climbing up the long poles
to get at the fruit.

Now I have two more hard words for you to learn, to distinguish our
two sorts of trees. We know them not merely by the difference of wood,
but of seed. First tell me how many cotyledons or lobes are in a seed?

There are two in all the seeds that ever I saw.

What! was that cocoa nut the same which you bought the other day?

No, that was all in one piece.

True, Willie; and you may recollect something about a date stone.

I do, indeed; that was single also. I see I must not be so sure another
time about what I know. Now I understand. Our new friends of the hard
shell stems, which bear fruit at all, have seeds of one piece instead
of two.

Quite so. Now a plant of one cotyledon in its seed, is said to be
_Monocotyledonous_, while that having two lobes is _Dicotyledonous_;
_mono_ meaning one, and _di_, two.

Then my Gum tree, and Rose tree, and Sweet Pea, are all Dicotyledonous;
but the nice Date Palm, the pretty Orchis, and the sweet Cocoa-nut, are
Monocotyledonous. But are there any plants which are neither one nor
the other?

There are some whose seeds are not to be distinguished, and are known
as _Acotyledonous_, or _without cotyledons_. Can you not name one?

I don’t know, unless you mean such as the Ferns, the Mosses, and the
Lichens on the rocks or decaying timber.

They are the very ones. We have now had examples of the three great
varieties of vegetation; _Monocotyledonous_, having one lobe to the
seed; _Dicotyledonous_, having two lobes; and _Acotyledonous_, without
any.

Will you now, dear father, explain the way in which the
Monocotyledonous plants differ from the Dicotyledonous, especially in
their system of growth?

I will, my boy, and we will begin this time with the seed.

Any one can tell where the plumula and rostellum of the Cocoa-nut
proceed, for we can see the two places in the shell, one at the top and
the other at the bottom. But do tell me what the white of the Cocoa-nut
is?

That sweet substance is the _Albumen_, to nourish the young embryo
inside. In most Monocotyledonous seeds, there is a lot of this
albumen - which is thus chemically changed to suit for food. In the Date
Palm this store-house is very hard, as you well know.

Is the Embryo different from others?

In general it is like an undivided cylinder, but in Grass and Corn, it
is a flat plate.

What! is Corn like the Palm, father?

Yes; for although it has a second, unshapen lobe, it is truly
monocotyledonous.

Well, father, how does the growth of the Mono folks go on?


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