The mature reproductive body of angiosperms
and gymnosperms. Seeds also represents
a resting stage which enables plants to survive
through unfavorable conditions. The germination
period varies widely from plant to plant.
|Representative types of seed: side and sectioned
views: (a) Winged endospermic seed of pine (Pine); (b) endospermic
castor oil seed (Ricinus communis; (c) non-endospermic broad
bean seed (Vicia faba); (d) endospermic "seed" of corn (maize;
Zea mays) (botanically this is really a fruit but the fruit
wall is thin and fused to the seed coat); (e) endospermic seed of
the onion (Allium cepa)
Seeds develop from the fertilized ovule. Every
seed is made up three main parts:
Flowering plants produce their seeds inside a fruit,
but the seeds of conifers like naked on the scales of the cone. Distribution
of seeds is usually by wind, animals or water and the form of seeds is often
adapted to a specific means of dispersal.
- Embryo. This is the essential living part of the
seed. It consists of a radicle, which gives rise to the root,
and a plumule, the growing part of a young shoot; the part containing
these two is called the hypocotyl. One or two seed leaves, or cotyledons,
grow out from the hypocotyl and may or may not be taken above the ground
during germination. Plants that produce one seed leaf are called monocotyledons
and those that produce two, dicotyledons.
The cotyledons may function, after germination, as leaves,
or they may (in seeds like the bean) contain the food-store.
- Food-store. This is the reserve of food on which
supplies the embryo and growing plant until it is able to make its own
food. The food-store may be in the cotyledons or in a part of the seed
called the endosperm It is this stored
food which is of nutritional value (see nutrition)
to humans and other animals.
- Testa or seed-coat. This the tough protective outer
covering the seed. It often has outgrowths which help in dispersal of