Seeds vary from
plant to plant in size and shape. The majority of seeds
have similar structures. Most seeds are surrounded by a
hard outside called the testa. Just beneath the testa is
the endosperm. The endosperm is the food stores of the
seed. It contains protein, fats, and starches which provide
energy for the developing seedling.
cotyledons provide a similar function. These are the seed
leaves and they also contain storage of food for the
developing plant. The cotyledons in some cases are major
photosynthetic producers during germination.
sandwiched between the cotyledons or pushed compactly
against the cotyledon are the remaining components of
the seed. The radical, the hypocotyls and the plumule
are found in most seeds. The radical is the first
structure to appear from the seed. It is the root
emerging and growing downward into the soil.
is part of the stem that will emerge from the seed and
is located between the radical and the cotyledon. The
plumule is the first bud of the germinating seed and
is located at the top of the seedling.
When a seed does not germinate immediately after leaving
the parent plant, it goes into a period of dormancy or
inactivity. Dormancy is sometimes required for a seed to be
viable. A seed can sometimes stay in a state of dormancy
for years. In order for a seed to come out of this dormancy
state, conditions have to be ideal. Ideal conditions depend
of the seed type but they include factors like: moisture,
temperature, light and in some cases even fire. For
example, the seeds of the lodgepole pine are only released
from the cone after being exposed to fire. Some seeds need
complete darkness to germinate, while others need to
germinate in the light.
Dormant seeds contain less than 10% water making them very
dry. This enables the seed to be preserved and survive to
the time of germination. At the time of germination a seed
begins to absorb water and it begins to swell. Also the
seed will begin to use its own food storage contained in
the endosperm. The seed coat will split and the radical
The radical is the first part of the seed that
emerges. It is the root
and begins to grow downward into the soil as soon as
it appears. Its primary purpose is to begin to absorb
water and nutrients for the developing seedling. The
radical is surrounded by a protective sheath called
the root cap. This protects the fast growing root as
it pushes through the soil. The portion at the tip of
the root where growth takes place is called the apical
meristem. Here, cells are elongated and rapidly
dividing promoting growth. As the root develops and
grows deeper, it is called a tap root and will produce
lateral roots which are offshoots of the primary root.
The tap root or primary root becomes a food storage
area and it helps in anchoring the plant in place. The
lateral roots increase the absorption of water for the
plant. Also present are root hairs. These are tiny
extensions off of the primary root and lateral roots
that also help in absorbing water and nutrients. At
the center of the root is the core or stele. Here is
where the conducting “tubes” of the plant
are located, called xylem and phloem. Water that is
absorbed in the roots gets transported upward to the
rest of the plant through the xylem tissue. Phloem
transports sugars from the top of the plant that is
produced during photosynthesis downward to the rest of
Flowering plants fall under two categories or classes. The
first class is monocots. The second class is called
eudicots. Grasses are considered to be moncots. Monocots
are called monocots because their seeds contain one
cotyledon (mono means one). Eudicot seeds have two
cotyledons (eu meaning true, di meaning two). Cotyledons
are housed in the seed and are the embryonic seed leaves.
Grasses are wind pollinated. Their flowers have no petals
or sepals. They have three carpels that are fused together
to one, and two separate stigmas. Usually in grasses, male
and female flowers are located on the same plant. The
majority of the grass seed is endosperm. Grasses are well
adapted to continuous grazing by animals. This is because
of the location of the shoot apical meristem in grasses.
The shoot apical meristem is the actively growing region of
the plant. Typically this region is located at the top of a
plant, but in grasses it is located near the bottom of the
leaves and stems. This is helpful because it allows for the
top portion of the grass to be eaten and the shoot apical
meristem is stimulated to grow.
There are about 8000 species of grasses. An interesting
example of a grass is bamboo, which is used in for
constructing various things like furniture. Examples of
grasses that we eat are: wheat (Triticum),
and rice (Oryza).
Peter H., Everert, Ray F., Eichhorn, Susan E. Worth
Introduction to Plant Biology. Mauseth, James D.
Jones and Bartlett Publishers. Sudbury, Massachusetts 1998.
Visual Dictionaries: Visual Dictionary of
Plants. Dorling Kindersley,
Inc. New York 1992.
B., Ross, Cleon W. Wadsworth, Inc Belmont, California 1992.
Understanding Science and Nature: Plant Life.
Time Inc. Book Company 1993