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Written Report, Morphoanatomy of Fruits and Seeds

II. Morphoanatomy of Seeds

D. Seed Germination

After fertilization and development, the embryo usually stops growing called the period

of dormancy. It begins to grow again when the seed germinates.

Internal Factors=changes in the amount of hormones like abscisic acid* or other

inhibitory chemicals, amount of stored food, viability

*Abscisic Acid (ABA) - A plant hormone associated with inhibition of growth and seed

dormancy in many plants

External Factors= water, temperature, light, food supply, soil acidity, oxygen and carbon

dioxide

1. Water Requirement

-The most common stimulus on breaking dormancy is water.

-A seed that absorbs water expands and burst its seed coat.

-Seeds will germinate only when there is enough water

-Seeds of rice and other aquatic or semiaquatic plants germinate only in soil that

is submerged in water.

2. Temperature Requirement

-The optimum temperature for germination: close to room temperature (25 C).

By: France Louie Jutiz


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-Germination can occur at temperatures as low as 0 C and as high as 45 C in

different species.

-In the process of stratification, the seeds of apple trees and most pines can be

artificially induced to germinate by wetting them and placing them in a

refrigerator.

3. Light Requirement

-Not all seeds are affected of light.

-The seeds of birch, certain grasses, and some varieties of lettuce require light

for germination.

-The seeds of other plants, such as geraniums and poppies, will germinate only

in the dark.

4. Special Requirements

-Many legumes contain seeds with hard seed coats, and the seeds of some

drupes are surrounded by a tightly sealed endocarp.

-Seeds with thick covering will germinate only after the seed coat is scratched or

cracked, or briefly soaked in concentric acid. Such treatments are called

scarification.

E. Seedling Development

-The first part of the embryo to emerge from the seed during germination is the radicle.



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-Seedling development varies depending on the function of the endosperm and the

location of the greatest meristematic activity in the embryo.

-Faster growth in the hypocotyls pushes the shoot and cotyledons through the soil

surface. Aboveground cotyledons become green and photosynthetic as in the garden

bean. (Epistogeal germination)

-Faster growth at the shoot apex keeps the cotyledons belowground as in the garden

pea. The cotyledons of garden pea quickly shrivel as they used up by the seedling.

(Hypogeal germination)

-Grasses have the most complex seedling development. The shoot apex grows out of

the kernel through the tube-like coleoptile, and the root apex grows through the tube-like

coleorhiza.

- Cleistogeal Germination: A special leaf that has a central umbrella like stalk forms

above the ground which protects the shoot from any damage. So the development of

the shoot cannot be seen (i.e. Combretum collinum seed)



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