Leaf : Photoperiodism :: Meristem :.........

Explanation

To solve the analogy "Leaf : Photoperiodism :: Meristem : ...", we need to understand the relationship between the first pair of terms, and then apply that relationship to the second pair.

### Step-by-Step Solution:

1. **Understanding Photoperiodism**:
- Photoperiodism refers to the response of plants to the relative lengths of light and dark periods in a day. It is primarily associated with the leaf, as leaves are the main sites for light perception.

2. **Role of the Leaf**:
...