Fig. 4.2-2. Transverse section of petiole of birch (Betula). This petiole has two layers of more-or-less lamellar collenchyma (it is not quite regular enough to be considered definitely lamellar collenchyma). Notice that the petiole also has fibers (the round red cells with white lumens near the top of the micrograph): the collenchyma must have been functional and provided plastic support while the leaf was elongating but the fibers are providing elastic support now that the petiole has grown to its mature size.