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Transverse sections of old basal stem segments of (A) Aristolochia ovalifolia (diameter approx. 8 mm), showing the non-compressed pith, the radial symmetry and partially lignified ray tissue (arrows in the rays pointing to the lignified portions); lignified rays cells are coloured in green, such as the vascular tissue, whereas non-lignified cells are coloured in pink; and (B) A. tomentosa, with radial symmetry (diameter approx. 11 mm). Sections are stained with carmine-green.
