The balloon- shaped structures called tyloses

Options

A. originate in the lumen of vessels
B. characterize the sapwood
C. are extensions of xylem parenchyma cells into vessels
D. are linked to the ascent of sap through xylem vessels

Explanation

### Step-by-Step Solution:

1. **Understanding Tyloses**: Tyloses are balloon-shaped structures that form within the xylem vessels of plants. They are important for plant health and defense.

2. **Formation of Tyloses**: Tyloses are formed as extensions of xylem parenchyma cells. When the plant is under stress, such as injury or infection, these cells can expand and protrude into the xylem vessels.

3. **Function of Tyloses**: The primary function of tyloses is to provide a defense mechanism for the plant. They help in:
- **Wound Healing**: When a plant is injured, tyloses can block the xylem vessels, preventing further loss of water and nutrients.
- **Inhibition of Infection Spread**: If there is an infection in the plant, tyloses can obstruct the flow of water through the affected xylem vessels, thereby preventing the spread of pathogens to other parts of the plant.

4. **Analyzing Options**: The question provides several options regarding the characteristics of tyloses:
- **Option 1**: Originate in the lumen of vessels - Incorrect, as tyloses do not originate in the lumen.
- **Option 2**: Characterize the sapwood - Incorrect, as tyloses are not specifically related to sapwood.
- **Option 3**: Extensions of xylem parenchyma cells into the vessels - Correct, as this accurately describes the formation of tyloses.
- **Option 4**: Linked to the ascent of sap through xylem vessels - Incorrect, as tyloses block water conduction rather than facilitate it.

5. **Conclusion**: Based on the analysis, the correct answer is **Option 3**, which states that tyloses are extensions of xylem parenchyma cells into the xylem vessels.