Eccentric deposition of secondary xylem in stems of the climber Ephedra campylopoda (Gnetales)

In Ephedra campylopoda, a woody climber of the Ephedraceae (Gnetales), the secondary xylem of the upper and lower sides of horizontal stems has the sa me structure. However, cambial activity in the lower side is greater, produ cing 1.5 times more xylem and 1.25 times more growth rings in thin stems an d 1.8 times more xylem in thick stems. Gelatinous fibres are not formed in the upper side or elsewhere in the xylem. I suggest that this difference in cambial activity does not change the flexibility of the stems, an importan t adaptation for a climber.