Velvety green beds appear on the walls during rainy season. Give reason.

Explanation

### Step-by-Step Solution:

1. **Identification of the Organisms**: The velvety green beds that appear on walls during the rainy season primarily consist of mosses, which belong to the Bryophyta division of plants.

2. **Conditions for Growth**: During the rainy season, the environment becomes moist and humid. This moisture is essential for the growth of bryophytes, as they thrive in damp conditions.

3. **Moisture Retention**: The walls retain moisture due to rain, creating a suitable habitat for these organisms. The moisture on the walls helps in the growth of various types of fungi and algae.

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