[Illustration: [Ovule]]
You will be glad to know that the little ovules at the heart of the
morning-glory and of all other flowers are single cells.
They have an outside wall and are filled with protoplasm.
When a pollen cell is formed from the inside of the anther, it separates
and is no longer connected with anything. This is not the case with the
ovule. It is fastened to the ovary by a little stem, for it will stay
there and grow; and it must have a way to get food from its parent
plant. It gets the food through this little stem.
You know what happens when the flower opens.
The bees bring pollen, and the protoplasm of the pollen joins that of
the ovule. As soon as this happens the ovule begins to change. We say it
_grows_. It gets the food to grow on from the mother plant through the
little stem which is fastened to the inside of the ovary.
The protoplasm in the ovule first divides and makes two cells instead of
one. These two cells do not entirely separate from each other. They stay
together to do their work. Soon each of them divides into more cells.
These cells again divide, and this continues until a great many cells
are formed. Meantime the ovule has increased in size as well as
complexity, and its cells do several different kinds of work. In the
morning-glory, for instance, some build a hard outer wall about the
young plant; this is the seed-case. Other cells form two little leaves;
others make a little stub of a stem. So the change goes on until the
single-celled ovule becomes a many-celled seed with a young plant rolled
up under its walls. If you open a morning-glory seed you can see this
little baby plant, only you will have to soak the seed first to soften
the food that is stored about the young plant.
The cells made this food to nourish it, and it stays dry and hard until
the rain moistens it in the spring, when it gets soft, like boiled
starch, and is then ready for the little plant to use. When the ovules
grow on one plant and the pollen comes from another, the seeds will
contain the protoplasm of two different plants.
Now protoplasm remembers the plant it came from, and tries to make the
new plant like it.
The ovule protoplasm tries to make the seed remember the plant it grows
on, and the pollen protoplasm tries to make the pollen remember the
plant it comes from.
So if the pollen comes from a plant bearing white flowers, it wants the
seeds to grow into white-flowered plants. But if the ovules which
fertilizes it grow on a pink-flowered plant, they try to make the seeds
grow into pink-flowered plants. Now what happens? Very likely some of
the flowers will be white and some of them pink. Some will take after
the plant the pollen came from and some after the one the ovule came
from. But sometimes the flowers will be a mixture of both plants and
will be pink and white.
[Illustration: [Ovule]]
The ovule is the mother part of the plant and the pollen is the father
part, and sometimes the seed-children take after the mother, sometimes
after the father, and sometimes after both.
This is very strange and we cannot quite understand it. How can the
protoplasm remember the exact shade and color of the plant it came from?
How can it make seeds that grow into plants just like the old plants?
Protoplasm, you are a great, a very great mystery!
By knowing about pollen and ovules we are able to help form a great many
lovely new flowers and fruits.
We get variegated flowers by fertilizing a flower of one color with
pollen from a flower of another color.
When we do this we must cover over the plant with a piece of netting
just before it blossoms, so the bees and butterflies cannot get ahead of
us and fertilize the plant. Then we must put a bit of pollen from one
flower on the stigma of the flower we want to experiment with.
We must always use the pollen from the same kind of a plant, however.
It would be of no use to put nasturtium pollen on a morning-glory
stigma, for instance, for it could not affect the ovule in the least.
The protoplasm knows in some way its own plant and will not fertilize
any other.
This is a very good thing, otherwise we might have a funny mixture of
all sorts of plants.
Many delicious fruits have been produced by fertilizing one plant with
pollen from another.
New varieties of grapes and berries are constantly obtained in this way.
If you live on a farm or have a garden, you might try to develop some
new kinds of berries or fruits. You might not succeed, but it would do
no harm to try.
[Illustration: [Ovule]]