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All flowers
are variations on a simple, basic plan. Some flowers are tiny
and hard to see: others are showy and flamboyant, like orchids
and roses. Some flowers grow in clusters, some bloom alone. All
flowers, however, have a protected ovary to contain the seeds,
and stamens to produce the pollen.
Flowers were developed by land
plants. Showy petals and sweet nectar are often produced to lure
insects to the blossoms.
Insects carry the pollen from flower
to flower, ensuring exchange of the information encoded in the
chromosomes.
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The Sepals Flowers have a well-defined
structure.
When the bud appears on the stem, we see the green
sepals. Sepals are the green parts that protect a flower
bud before it opens. There is usually one sepal for each petal.
All together the sepals are called the calyx (pronounced
kay-licks).
After the flower opens the sepals can often still be seen
behind the petals. The sepals protect and sometimes support
the corolla (all the petals together).
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The petals are really advertisements for insects, signaling "Nectar
Here!" Nectar is secreted at the base of the petals on the
inside of the flower. The nectar is used to lure insects to
the flower, and it is placed so that the insects get a dusting
of pollen as they crawl to the nectar and lap it up. Then the
insects fly off to other flowers, taking the pollen from the
first flower with them.
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Let's look more closely at the parts of the flower
that make the seeds.
The inside of the flower holds the reproductive
parts. The stamens, which are orange in our diagram, produce
the pollen, which is represented by yellow dots. The pistil,
which is the green part in the center of the flower, is considered
to be the female part: you can see the unfertilized seeds waiting
in the ovary at the bottom of the pistil.
The Pistil
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The pistil is the part of the flower that produces the
seeds.
It consists of three parts:
- The stigma -- the pollen grains stick to this small sticky
pad
- The style -- the pollen grains grow down through this stem-like
cylinder
- The ovary -- this is where the young seeds wait for the chromosomes
in the pollen, and where they grow into mature seeds
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The wall of the ovary protects the developing seeds. When the seeds are
mature they are often found in some sort of seed case, a pod,
perhaps, or a fruit or berry. Animals and birds who eat the
fruit scatter the seeds abroad. |
The Stamen
 Stamens are slender structures that hold the pollen
They consist of two parts:
- The
anther -- a small case
in which the pollen
grains form
- The
filament -- a slender
stem that supports the
anther
The pollen grains form in the anthers, which open when the
pollen is mature. The pollen is a fine, powdery, golden dust
that is easily picked up by an insect or a finger.
A
flower may receive
pollen from many
different kinds of
plants. However, only
pollen grains from the
same kind of plant
will begin to grow..
The pollen sticks to
the stigma and a tiny
tube grows down from
the pollen grain. When
it reaches an
unfertilized seed, the
sperm cells in the
pollen slide down the
tube and fertilize the
seed. It may take a
day or two for the
little tube to grow.
Once the seed is
fertilized, it stays
in the ovary and
matures. The seed will
have two parts: a cell
that is ready to grow
into a new plant, and
a food supply to help
the new plant to grow.
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