Which term denotes the horizontal movement of substances within the xylem via ray cells?

• A. Radial transport
• B. Transpiration
• C. Guttation
• D. Evaporation

Answer: (A)

Radial transport is the horizontal movement of water and dissolved minerals through xylem ray cells. Xylem rays are vertical files of parenchyma that run across the xylem, linking vessels and tracheids and allowing resources to move sideways as needed. This sideways flow helps distribute water and solutes across the xylem’s cross-section and toward neighboring tissues, complementing the mostly vertical ascent of water from roots to leaves.

Transpiration describes water loss from leaves, guttation is water exuded at leaf margins due to root pressure, and evaporation is the general process of liquid water turning to vapor. None of these describe the lateral movement within the xylem via ray cells.