The correct option is D Are always open
Guttation is the loss of water through water stomata (hydathodes) in solution form as a dilute solution of mineral salts. When the absorption of water exceeds transpiration i.e., when plants are absorbing actively, a positive root pressure is built up under the influence of which excess water simply oozes out through the dead ends of xylem tracheids and vessels. A loose collection of cells called as epithem, present at the dead ends of xylem tracheids and vessels. The epithem cells do not regulate opening and closing of hydathodes. Thus, hydathodes are unregulated openings and are always open. Thus, the correct answer is option D.