Most plants grow from seeds. These seed plants fall into
two groups, angiosperms and gymnosperms. Angiosperms are the flowering plants.
Their seeds develop inside a female reproductive part of the flower, called the
ovary, which usually ripens into a protective FRUIT. Gymnosperms
(conifers, Ginkgo, and cycads) do not have flowers or
ovaries. Their seeds mature inside cones. Seeds may be carried away from the
parent plant by wind, water, or animals.
A seed is the first stage in the life cycle of a plant. Protected
inside the tough seed coat, or testa, is the baby plant, called an embryo.
Food, which fuels germination and growth, is either packed around the embryo or
stored in special seed leaves, called cotyledons.
Seeds are not the only means of reproduction. Some plants create
offshoots of themselves – in the form of bulbs, tubers, corms, or
rhizomes – that can grow into new plants. This type of reproduction is
called vegetative reproduction. As only one parent plant is needed, the
offspring is a clone of its parent.
A bulb is an underground bud with swollen leaf bases. Its food
store allows flowers and leaves to grow quickly. New bulbs develop around the
old one.
A tuber is a swollen stem or root with buds on its surface. When
conditions are right, the tuber’s food store allows the buds to
grow.
A corm is a swollen underground stem that provides energy for a
growing bud. After the food in the old corm is used up, a new corm forms above
it.
A rhizome is a horizontal stem that grows underground or on the
surface. It divides and produces new buds and shoots along its branches.
GERMINATION OF A RUNNER BEAN
Most seeds require damp, warm conditions in order to sprout. During
germination, the seed absorbs water and the embryo starts to use its food
store. A young root, or radicle, begins to grow downward. Then a young shoot,
or plumule, grows upward. This develops into the stem and produces leaves. The
first leaves, called seed leaves or cotyledons, fuel the early growth until the
plant’s true leaves appear.
A flower’s ovary usually develops into a fruit to
protect the seeds and help disperse them. A fruit may be succulent (fleshy) or
dry. Fruit is often tasty and colourful to attract fruit-eating animals. Its
seeds can pass through an animal unharmed, falling to the ground in droppings.
Seeds may also be dispersed on animals’ coats, by the wind, or by the
fruit bursting open.
The seeds of dry fruits are dispersed in various ways. Peapods are
dry fruits that split and shoot out their seeds by force. The hogweed fruit
forms a papery wing around the seed, helping it to float on the breeze. The
strawberry is a false fruit, but it is covered by tiny dry fruits, each with a
seed.
Fleshy, brightly coloured, and often scented, succulent fruits are
designed to attract the animals that eat and disperse them. Fleshy fruits such
as apricots and cherries have a woody stone or pip that protects the seed.
Called drupes, these fruits form from a single ovary. Many drupes, formed from
many ovaries, may cluster to form a compound fruit, such as a raspberry.
