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Secondary Thickening : Aristolochia durior (Aristolochia)

a. Cross-section through a young stem. The vascular bundles are separated. The interfascicular cambium is not yet developed. Between periphery and the ring of vascular bundles a collenchyma ring of several cell layers thickness exists. Compare the different thicknesses of collenchyma cells (and the vascular bundle cells) with the central parenchyma cells. b Cross-section through a one year old twig. Xylem elements become more and more important for the strengthening. The number of vascular elements is higher than in a., forming a nearly complete vascular cylinder that is just here and there interrupted by parenchyma cells (pith rays). The collenchyma has become unimportant. (R. DUDEN, 1985)


© Peter v. Sengbusch - b-online@botanik.uni-hamburg.de