Tyloses are balloon-like outgrowths in the lumen of secondary xylem tracheids and vessel of duramen region. These are actually:

Tyloses are the balloon - like outgrowths which forms due to the ingrowth of adjacent xylem parenchyma cells into the lumen of xylem vessels. This structure checks the plants from being damaged in the stressed condition like drought or infection by falling from the sides of the cells. So, the correct answer is option D (Ingrowth of xylem parenchyma).