Lower and upper
branches of Coast Redwood display very different leaf shapes, here shown
against bark of a fallen tree. Large, wide sprays are typical of lower branches
and small, scale-like leaves are typical of canopy branches. A gradient of
intermediate leaf shapes occurs with increasing height above ground. Water
transport has been shown to be the causal factor, causing leaf stress
in high branches. (See Koch, Sillett, et al., Nature 428:851-854, 22
Apr. 2004.)
