THE CONCEPT OF GROWTH AND DEVELOPMENT.
Growth and development in plants usually begins with germination
Germination is the process whereby seeds develops into seedling.
Seed is a structure formed after fertilization of an ovule.
Parts of the seeds.
❖ An embryo: this part consists of radicle that develops into a root
and plumule develops into a shoot after germination.
❖ A seed coat: this part is also known as a testa. It is a protective
layer surrounding a seed.
❖ Cotyledons: This part grows to form embryonic first leaves after
germination
❖ Micropyle is the pore through which water enters the seed during
seed germination.
❖ Hilum: This is a scar that shows the seed's point of attachment to
the ovary wall.
Figure4.1; structure of (a) dicot (b) monocot seed
Necessary conditions for germination
❖ Water,
A seed absorbs water through the micropyle. Water plays an important
role during seed germination. When a seed absorbs water, the embryo
cells enlarge due to pressure. Such action leads to the rapture of the seed
coat. Water softens the seed coat, hence Increases seed permeability.
Water also activates enzymes necessary for seed germination and growth
❖ Air(oxygen)
Oxygen gas is necessary for aerobic respiration to generate energy that is
required for the growth of the embryo of a seed.
❖ Optimum temperature
Seeds need the optimum temperature to germinate. The seed of each
plant species has its optimum temperature for germination. Temperature
is essential for the activation of enzymatic reactions during respiration.
Respiration is important as it provides the energy required for
germination.
❖ Light, required for photosynthesis
Internal factors that affect germination
❖ Enzymes. Break down food reserves in the cotyledons or
endosperm into soluble form
❖ Hormones such as auxins hormones acts as growth stimulators
❖ Viability. Refers to the ability of the seed to germinate. Only alive
and healthy seeds will germinate
Types of germination
There are two types of germination which are;
❖ Epigeal germination
❖ Hypogeal germination
Epigeal germination is the type of germination whereby cotyledons are brought
above the soil level. This type of germination occurs in dicotyledonous plants
such as;
❖ Beans
❖ Groundnuts
❖ Okra
❖ Amaranthus spp
Figure;4.2: stages of epigeal germination
Hypogeal germination is the type of germination in which the seed
cotyledons remain underground. It occurs in plants such as maize and
pigeon peas.
Figure; 4.3: stages of hypogeal germination of maize grain
Coleoptile is the sheath which protects plumule in maize (plumule
sheath).
Coleorhiza is the sheath which protects radicle as it emerges through the
maize grain.
