The casparian strip is usually composed of

Options

A. lignin
B. pectin
C. cutin
D. suberin

Answer

### Step-by-Step Solution:

1. **Understanding Casparian Strips**:
- Casparian strips are specialized structures found in the roots of dicotyledonous plants, specifically in the endodermis layer. They play a crucial role in regulating the movement of water and solutes into the vascular system of the plant.

2. **Composition of Casparian Strips**:
- The primary component of Casparian strips is **Suberin**, a waxy substance that provides a barrier to the passive flow of water and solutes.

3. **Distinction from Other Cell Walls**:
- Unlike typical cell walls that are often composed of lignin, the Casparian strip is chemically distinct. While lignin may occasionally be present, it is not a primary component of the Casparian strip.

4. **Function of Casparian Strips**:
- The presence of suberin in the Casparian strip prevents the free passage of water and solutes, ensuring that all substances entering the vascular system must pass through the cell membranes of the endodermal cells, allowing for selective absorption.

5. **Conclusion**:
- Based on the information, we conclude that the Casparian strip is primarily composed of **Suberin**.

### Final Answer:
The Casparian strip is usually composed of **Suberin**.

---