Some of the unusual functions performed by specialised stems are:

Options

A. protection
B. reproduction
C. photosynthesis
D. all of these

Answer

**Step-by-Step Text Solution:**

1. **Understanding the Role of Stems:**
- Stems are the above-ground parts of the plant that develop from the plumule. They bear nodes and internodes and support the plant by holding leaves, flowers, and fruits.

2. **Normal Functions of Stems:**
- The primary functions of stems include:
- Providing support to the plant.
- Conducting water and minerals from the roots to the leaves and fruits.
- Transferring food produced in the leaves to other parts of the plant via phloem.

3. **Specialized Functions of Modified Stems:**
- Stems can undergo modifications to perform unusual functions. The question asks about these specialized functions, which include:
- **Protection:** Some stems are modified into thorns (e.g., in citrus and bougainvillea) to protect the plant from herbivores.
- **Reproduction:** Certain modified stems, such as tubers (e.g., potatoes) and rhizomes (e.g., ginger), assist in asexual reproduction. Other weak stems like runners and stolons can also develop into new plants.
- **Photosynthesis:** In some plants, like Opuntia, stems can be modified into phylloclades, which take over the function of photosynthesis when leaves are absent.

4. **Conclusion:**
- Since all three functions (A: Protection, B: Reproduction, C: Photosynthesis) are performed by specialized stems, the correct answer to the question is D: All of these.