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
soil?
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
grow.
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
bark?
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?