Seed formation and germination
Fertilization
Once the pollen grains reach the stigma, each grain produces a long tube called the pollen tube. The tube, which carries the male gamete, pushes its way down through the style and into the ovule through the micro Pyle. The male gamete fuses with the egg cell in the ovule, giving rise to the zygote.
Seed formation
After fertilization, the ovule develops into the seed. The zygote grows into an embryo and the ovary forms the fruit. The embryo consists of a radical, a plumule and one or two cotyledons, or seed leaves. It lies dormant in the seed until conditions are favorable. Under favorable conditions, the radicle gives rise to the root, while the plumule forms the shoot. The growing root and shoot utilize the food stored in the cotyledons.
Seed germination
This s the process by which the dormant embryo becomes active and grows into a seedling. At first, the seed absorbs water and swells up. Then the seed coat ruptures and the radicle and plumule emerge out of the seed. The radicle grows downwards, while the plumule grows up words. Initially, the cotyledon supplies food to the growing embryo. Soon, the radicle develops into the root and stars absorbing water and minerals from the soil, while the leaves grow out of the plumule to manufacture food for the seedling.
Seeds germinate only when they are mature. They require water, oxygen and the right range of temperature for germination.
Experiment
Fill three –fourths of a jar with water. Secure three bean seeds to a wooden ruler with the help of rubber bands. Immerse the ruler in the jar of water in such a way that the lowest seed is submerged in water, the middle one is only half-submerged and the top one is above the water. Put the jar in warm place, away from direct sources of heat. Over the next few days, make sure that the level of water remains the same by adding water to the jar, Notice which seeds germinate and explain why.
Soak are some gram (or pea), maize and bean seeds overnight. Next morning, try to remove the seed coat from one seed of each variety. You will notice there are two cotyledons inside the seed coat of the gram and been seed. You will not be able too peel off the seed coat of the maize seed because it is fused with the wall of the one-seeded fruit. Also, the maize seed will not split because it contains only one cotyledon.
Plant the rest of the seeds in moist cotton oar a pot of soil and wait for the radicle and plumule to come out and grow. You will see that the gram and maize seeds will stay in contact with the soil or wet cotton, but the bean seeds will be lifted above the soil. You can experiment with other seeds like gourd, papaya and garden plants to see which remain in contact with the soil and which are lifted up.
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