Sieve tubes are characteristed by

Options

A. Absence of septa
B. Simple oblique septa
C. Perforated longitudinal walls
D. Perforated oblique septa (Sieve plate)

Answer

### Step-by-Step Text Solution:

1. **Understanding Sieve Tubes**: Sieve tubes are specialized structures found in the phloem of flowering plants. They are responsible for the transport of nutrients, particularly sugars produced during photosynthesis.

2. **Structure of Sieve Tubes**: Sieve tube elements are elongated cells that are connected end to end, forming a continuous tubular structure. This arrangement is crucial for their function in transporting substances throughout the plant.

3. **Characteristics of Sieve Tubes**:
- **Absence of Septa**: This option suggests that sieve tubes do not have any internal divisions, which is incorrect.
- **Simple Oblique Septa**: This option implies that there are simple diagonal partitions, which is also incorrect.
- **Perforated Longitudinal Walls**: This suggests that the walls have holes running along their length, which is partially correct but not specific enough.
- **Perforated Oblique Septa (Sieve Plates)**: This is the correct characteristic. Sieve plates are specialized structures at the end of sieve tube elements that have pores, allowing for the flow of sap between adjacent sieve tube cells.

4. **Conclusion**: The defining characteristic of sieve tubes is the presence of **perforated oblique septa**, known as sieve plates, which facilitate the movement of nutrients.

### Final Answer:
Sieve tubes are characterized by **perforated oblique septa (sieve plates)**.

---