Define the following :
Double fertilization

Explanation

**Step-by-Step Solution:**

1. **Definition of Double Fertilization**:
Double fertilization is a unique fertilization process that occurs in flowering plants (angiosperms).

2. **Mechanism of Double Fertilization**:
- In this process, one male gamete (sperm cell) fuses with one female gamete (egg cell) to form a zygote. This is the first fertilization event.
- Simultaneously, the second male gamete fuses with two polar nuclei present in the embryo sac to form the endosperm. This fusion is known as triple fusion.
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