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Examples of perpendicular ridges. The epidermal cells of the petals of Yunnan rhododendron (a,b) (Rhododendron yunnanense) and the daisy Ursinia calendulifolia (c,d) are striated but the ridges form perpendicularly to the axis of elongation of the cells (compare with figure 1b,e). (b,d) Scanning electron microscope images; scale bars, 10 µm. (Online version in colour.)
