Describe the process of Fertilization in angiosperms.
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Angiosperms, or flowering plants, undergo a unique process called double fertilization. After pollination brings a pollen grain to a flower's female reproductive structure (carpel), a pollen tube releases two sperm cells. One of these sperm cells unites with an egg cell to produce a diploid zygote
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Fertilisation is the fusion of the female gamete (Egg or Ovum) produced in the embryosac and the male gamete produced in the pollen tube by the pollen grain.


The process of fertilisation in flowering plants was first discovered by Strassburger in 1884. After pollination, the exine of the germinating pollen grain ruptures and the intine grows out into a tube called the pollen tube. The formation of the pollen tube takes place through the germ pore of the exine. The stigma secretes a sugary substance and stimulates the growth of the pollen tube. The pollen tube enclosing the tube nucleus and the generative cell ruptures the stigma and passes through the style. The generative cell divides and produces two male gametes while the tube cell disappears. After reaching the ovary, the pollen tube enters into the ovule. Depending upon its place of entry, three types of fertilization have been recognised. They are :
Porogamy:
This is the commonest type of fertilization seen in angiosperms. Here the entry of the pollen tube into the ovule takes place through the micropyle.
Chalazogamy:
In plants like Casuarina, the entry of pollen tube takes place through the chalaza.
Mesogamy:
In Cucurbita, pollen tube enters the ovule through the integuments. After the pollen tube enters the embryosac, its apex dissolves and the male gametes are liberated. One of the male gametes fuses with the egg and produces a diploid zygote (Strassburger, 1884) which by further division develops into an embryo. The other male gamete fuses with the diploid secondary nucleus (fusion product of two polar nuclei) and produces a triploid (3n) primary endosperm nucleus (Nawaschin, 1898). This is called double fertilization.
Thus, there are three fusions occur in the embryosac.
1. The fusion of two polar nuclei to form secondary nucleus
2. The fusion of one male gamete with the egg.
3. The fusion of other male gamete with the secondary nucleus to form primary endosperm nucleus. Hence, the process is called triple fusion.
Post fertilisation changes:
As a result of fertilisation, the following changes are observed in a flower:
1. A diploid zygote is formed and develops into an embryo which is the future plant.
2. The triploid endosperm tissue serves as a source of nutrition for the developing embryo.
3. The ovule becomes seed.
4. The ovary becomes fruit.
5. The antipodals and synnergids disintegrate before, during or immediately after fertilisation in most of the plants.
6. The outer and inner integuments of ovule becomes the testa (seed coat) of the seed.
7. Petals and sepals fall off. (In some, the sepals persist in the fruit, e.g., Solanum.
In certain cultivated varieties of banana, orange, apple etc., the ovary may develop into the fruit without fertilization. This process is called parthenocarpy. Parthenocarpic fruits rarely contain seeds.


The process of fertilisation in flowering plants was first discovered by Strassburger in 1884. After pollination, the exine of the germinating pollen grain ruptures and the intine grows out into a tube called the pollen tube. The formation of the pollen tube takes place through the germ pore of the exine. The stigma secretes a sugary substance and stimulates the growth of the pollen tube. The pollen tube enclosing the tube nucleus and the generative cell ruptures the stigma and passes through the style. The generative cell divides and produces two male gametes while the tube cell disappears. After reaching the ovary, the pollen tube enters into the ovule. Depending upon its place of entry, three types of fertilization have been recognised. They are :
Porogamy:
This is the commonest type of fertilization seen in angiosperms. Here the entry of the pollen tube into the ovule takes place through the micropyle.
Chalazogamy:
In plants like Casuarina, the entry of pollen tube takes place through the chalaza.
Mesogamy:
In Cucurbita, pollen tube enters the ovule through the integuments. After the pollen tube enters the embryosac, its apex dissolves and the male gametes are liberated. One of the male gametes fuses with the egg and produces a diploid zygote (Strassburger, 1884) which by further division develops into an embryo. The other male gamete fuses with the diploid secondary nucleus (fusion product of two polar nuclei) and produces a triploid (3n) primary endosperm nucleus (Nawaschin, 1898). This is called double fertilization.
Thus, there are three fusions occur in the embryosac.
1. The fusion of two polar nuclei to form secondary nucleus
2. The fusion of one male gamete with the egg.
3. The fusion of other male gamete with the secondary nucleus to form primary endosperm nucleus. Hence, the process is called triple fusion.
Post fertilisation changes:
As a result of fertilisation, the following changes are observed in a flower:
1. A diploid zygote is formed and develops into an embryo which is the future plant.
2. The triploid endosperm tissue serves as a source of nutrition for the developing embryo.
3. The ovule becomes seed.
4. The ovary becomes fruit.
5. The antipodals and synnergids disintegrate before, during or immediately after fertilisation in most of the plants.
6. The outer and inner integuments of ovule becomes the testa (seed coat) of the seed.
7. Petals and sepals fall off. (In some, the sepals persist in the fruit, e.g., Solanum.
In certain cultivated varieties of banana, orange, apple etc., the ovary may develop into the fruit without fertilization. This process is called parthenocarpy. Parthenocarpic fruits rarely contain seeds.
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