Phyllotaxis is

Options

A. Mode of leaf arrangement on stem
B. Types of roots
C. Arrangement of sepals and petals in a flower
D. Type of ovary.

Answer

### Step-by-Step Solution:

1. **Understanding the Term "Phyllotaxis":**
- The term "phyllotaxis" is derived from two Greek words: "phyllo" meaning leaf and "taxis" meaning arrangement. Therefore, phyllotaxis refers to the arrangement of leaves on a stem.

2. **Identifying the Correct Definition:**
- Among the given options, we need to identify which one accurately describes phyllotaxis. The options provided are:
- A) Mode of leaf arrangement on stem
- B) Types of roots
- C) Arrangement of sepals and petals in a flower
- D) Type of ovary
- The correct definition of phyllotaxis is option A, which states it is the mode of leaf arrangement on the stem.

3. **Explaining the Types of Phyllotaxis:**
- There are three main types of phyllotaxis:
- **Whorled Arrangement:** Leaves are arranged in a circle around the stem at a single node.
- **Opposite Arrangement:** Two leaves are present at each node, directly opposite to each other.
- **Alternate or Spiral Arrangement:** Leaves are arranged alternately along the stem, creating a spiral pattern.

4. **Historical Context:**
- The term phyllotaxis was coined by the scientist Charles Bonnet, who studied the patterns of leaf arrangements in plants.

5. **Conclusion:**
- Based on the definitions and types discussed, we conclude that phyllotaxis specifically refers to the arrangement of leaves on a stem, making option A the correct answer.