Cross-Section Through a Lignified Shoot of Dracaena fragrans, an African dragon tree: Atypical secondary thickening. 1, 2. Bark, primary tissues at the outside, secondary tissues at the inside. Secondary meristems (lateral meristems, extrafascicular cambium) are generated in a zone that separates the bark and the parenchyma of the central cylinder thus causing the 'atypical' secondary thickening and the formation of secondary vascular bundles. In that way, 'primary vascular bundles' develop that later on become 'secondary vascular bundles'. 3, 4. Secondary vascular bundles (with tracheids located centrally and a peripherous vascular bundle sheath) and parenchymatic ground tissue of the central cylinder. (slide preparations: G. SEEHANN, 1986).