Question

describe the process of fertilization in an angiosperm plant?​

Answer 1

Answer:

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.

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