Name the protective substance present in the pollen envelope to tide over adverse condition.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Pollen Envelope**: The pollen grain has an outer envelope known as the pollen envelope, which consists of two main layers: the exine (outer layer) and the entine (inner layer).

2. **Identifying the Layers of Exine**: The exine is further divided into two parts: ect-exine (outer layer of the exine) and end-exine (inner layer of the exine).

3. **Recognizing the Protective Substance**: The exine is primarily composed of a substance called sporopollenin. This substance is crucial for the protection of the pollen grain.

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