Ecological trends were found concerning earlywood vessel diameter. Large earlywood vessel diameters (>150 pm) are characteristic of the lianas (Aristolochia gigantea, A. manshuriensis, A. macrophylla).
The bark of Asarum europaeum is unique: Vascular bundles are isolated in a ring and a peripheral continuous phloem. Cortical fibers and phellem are absent. (Figs. 1 and 16). All other species have a cortical fiber band which is broken in older individuals, and a periderm. The periderm is thin in Aristolochia clematitis (Fig. 17), Aristolochia pallida (Fig. 18) and large on the lianas Aristolochia gigantea (Fig. 19), A. manshuriensis and A. macrophylla (Fig. 20). The cortical fibers band consists of septate fibers with small, slit-like pits (Fig. 21).
Left Fig. 16. Single vascular bundle. The phloem consists of small sieve-tube elements and larger parenchyma cells. The bundle is surrounded by large parenchyma cells. Rhizome of a 5 cm-high hemicrypto-phyte, understory of a beech forest, mountain zone, Switzerland. Asarum europaeum, transverse section.
Right Fig. 17. Phloem between ray dilatations. Older sieve-tube elements have collapsed (dark irregular zones). A piece of a former fiber-belt is present outside the ray dilatation in the cortex. The periderm is small. Rhizome of a 40 cm-high hemic-ryptophyte, abandoned vineyard, hill zone, Austria. Aristolochia clematitis, transverse section.
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Left Fig. 18. Pieces of a former fiber belt in the cortex. The phellem is small. Rhizome of a 30 cm-high hemicryptophyte, abandoned vineyard, hill zone, Provence, France. Aristolochia pallida, transverse section.
Right Fig. 19. Bark with an extremely large rPh phellem. The former fiber belt in the cortex is bridged of sclerenchyma cells. Older a sieve-tube elements in the phloem are collapsed. Shoot of a 2 m-high tree, tropical Xy green house, Botanical Garden, Basel, Switzerland. Aristolochia gigantea, transverse section.
Left Fig. 20. Bark with a multilayered phellem. The former fiber belt is broken and the gaps are filled with thin-walled parenchyma cells. Older sieve-tube elements in the phloem are collapsed. Old stem of a 4 m-long liana, Botanical Garden, Bern, hill zone, Switzerland. Aristolochia macro-phylla, transverse section.
Right Fig. 21. Septate fibers of the fiber belt in the cortex. Shoot of a 2 m-high tree, tropical green house, Botanical Garden, Basel, Switzerland. Aristolochia gigantea, radial section.
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