Seeds are only one way that plants are reproduce.
Plants can also spread by growing bigger and
spreading out across the ground. At some point
the plant becomes so big that different parts of
it are capable of growing by themselves. The
plant may then split or the mature parts simply
fall off. These off-spring are usually called
"clones," because they are genetically identical
to their parent plants. Classic examples of these
clones include familiar garden plants like
strawberries (they have long roots called stolens
that spread out from existing plants). Another
special way of reproducing plants is called
grafting. When plants are grafted the green top
of one plant is combined with the living roots of
another plant. This process can establish plants
that might not be able to reproduce on their own.
Nuts, apples, and stone fruits are often grafted
(sometimes you can see a strange line near the
base of the tree where the width of the tree
changes or maybe the bark is a different color).
So, back to your watermelons and grapes.
Given those options, if you were a farmer how
would you grow more?
Hint: You've probably
already got a whole field full of healthy
watermelons and grapes to work with.
How do you plant seedless fruit? You don't. Plants
that produce seedless fruit ("sterile" plants) do
not occur in nature since they cannot reproduce.
Scientists have created certain special varieties
of commercial fruit to grow without seeds (e.g.
oranges, grapes) or with smaller, reduced seeds
(bananas, "seedless" watermelons) in order to make
it more convenient for humans to eat them.
However, these varieties must be specially
cultivated since they cannot be re-planted from
For seedless grapes, new plants must
be made from existing ones. The easiest method
involves slicing the stem of an adult plant
diagonally and cutting sections from it.One end of
each cutting can then be dipped in a rooting
hormone. (Yes, plants have growth hormones!
Rooting hormones stimulate the production of
roots.) The cuttings are planted and eventually
grow into new plants that produce fruit. Grapes
from seedless plants are small, and must be
treated with plant growth hormone in order to
ripen to normal size. The process of growing
seedless grapes is a form of asexual reproduction,
as the new plant is basically a genetic clone of
the original parent plant. Some seedless grape
varieties have been grown this way since Roman
times (a grape plant that is 2,000 years old)!
Wild grape plants reproduce sexually, by a process
called pollination. In sexual reproduction, male
gametes combine with female gametes to produce a
new organism which has half of its genetic
identity from the mother and half from the father.
Find a book about general plant biology ("botany")
look on the web and try to answer these
questions: What parts of plant flowers contain the
male gametes (pollen)? What parts contain the
female gametes (eggs)? How does pollination occur
(that is, how does the pollen make it to the
In order to create seedless
watermelon plants, normal seed-producing plants
which have 2 sets of chromosomes are pollinated
with pollen from plants that have been engineered
to have 4 sets of chromosomes. The resulting seeds
produce plants ("hybrids") that have 3 sets of
chromosomes. These hybrids are sterile, which
means they produce seedless fruit. In this way, a
seedless watermelon can be grown from
Scientists are working on new ways to
produce seedless watermelon, tomatoes, eggplant,
cherries, cucumbers and green peppers.
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