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.