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,Tobacco stem: Continuous vascular cylinder is derived from cambium No isolated vascular bundles No secondary growth of internal phloem Cross-section of tobacco (Nicotiana sp.) outer portion of stem whose cambium produces a continuous cylinder of secondary vascular tissues.,接骨木次生生长,Secondary stem growth This cross-section of a three year old woody stem of basswood (Tilia sp.) shows a small region of pith to the axial interior surrounded by three distinct growth rings. Traversing the growth rings are wood rays which continue out into the phloem as phloem rays,
