Vessels of heart wood are blocked by
A.Hydathodes – the small pores, present on the surface of grass leaves are called hydathodes. They perform guttation.
B.Tyloses - The balloon shaped structures formed in the vessels of heart wood due to the intrusion of secondary xylem parenchyma cells are tyloses. They block the vessels of heart wood.
C. Stomata – the small or minute pores present in the epidermis of leaves, young stems, etc., are called Stomata. They perform transpiration.
D.Latex – a milky fluid obtained laticiferous tissues. They are used in making rubber.
So, the correct option is ‘Tyloses’.