The balloon-shaped structures called tyloses: Are extensions of xylem parenchyme cells into vessels; Are linked to the ascent of sap through xylem vessels; Originate in the lumen of vessels; Characterize the sapwood

Tyloses are the balloon-shaped extension of xylem parenchyma cells of vessels in the heartwood. These structures are mostly found in drought exposed plants or in infected plants wherein they serve to reduce the surface available for transport in the conducting element and thereby acting as morphological defenses.Therefore, the correct answer is option A.