Morphological adaptations of tracheid structure to water stress gradients in the crown of Sequoiadendron giganteum.

Mean radial diameter of tracheids in young branches of a 90 m Sequoiadendron giganteum decreases linearly with height along a gradient correlated linearly with decreasing xylem pressure potential. These smaller tracheid diameters provide strength to resist strong mechanical tensions in the xylem column and hypothetically allow greater efficiencies of water conduction. Tracheid length is not significantly correlated with either water stress or tracheid diameter.