NEAR-VESSELLESSNESS IN EPHEDRA AND ITS SIGNIFICANCE

Wood of two specimens of Ephedra from high alpine localities is nearly vesselless: E. gerardiana from 4,750 m in Tibet, and E. rupestris from 4,300 m in Argentina. Ephedra gerardiana from lower elevations in the Himalayas has more vessels, although even there they are not abundant. Instances in other species of Ephedra in which extensive areas of latewood or even entire growth rings are vesselless are cited; these tend to occur in high deserts with climates somewhat less extreme than those of the alpine localities. Near-vessellessness is interpreted as an adaptive condition in which the proportion of tracheids, conductively safer than vessel elements, reaches a maximum. Near-vessellessness in Ephedra wood is probably reversible within limits, and should be likened to production of latewood to the exclusion of earlywood. Comparisons are offered to dicotyledons in which abundance of vessels is lowered with respect to ecological extremes.