Which of the following is not a stem modification

Options

A. Thorns of citrus
B. Tendrils of cucumber
C. Flattened structures of Opuntia
D. Pitcher of Nepenthes

Answer

To determine which of the following options is not a stem modification, we will analyze each option provided in the question.

**Step 1: Analyze the first option - Thorns of Citrus**
- Thorns of citrus plants are indeed a modification of the stem. They are sharp, stiff structures that have lost their growing points and serve primarily for protection against herbivores. Additionally, they help reduce transpiration, making them adaptations suitable for arid environments.

**Step 2: Analyze the second option - Tendrils of Cucumber**
- Tendrils in cucumbers are also a modification of the stem. These tendrils arise from the terminal bud and are used for support and climbing. They help the plant to attach to structures for better growth and stability.

**Step 3: Analyze the third option - Flattened structures of Opuntia**
- The flattened structures of Opuntia, known as phylloclades, are modified stems that have taken over the function of leaves for photosynthesis. They are adaptations to arid conditions, where the actual leaves have been reduced to spines to minimize water loss. Thus, they are also considered stem modifications.

**Step 4: Analyze the fourth option - Pitchers of Nepenthes**
- The pitchers of Nepenthes are not a modification of the stem; instead, they are a modification of the leaf lamina. Nepenthes is an insectivorous plant, and its pitcher structure is designed to trap insects for nutrient absorption, especially in nitrogen-deficient environments.

**Conclusion:**
Based on the analysis, the option that is not a stem modification is **D: the pitchers of Nepenthes**. This structure is a modification of the leaf, not the stem.

---