Tracheary elements appear already in the early stages of in vitro organogenesis and precede the formation of meristemoids and shoot primordia which further develop into shoots. Thus this process can be considered as an important indicator of potential, organogenic capability of the explants. The aim of this study was to investigate the effect of auxin (IAA), cytokinin (BAP), sucrose and the light conditions (light with 16-h photoperiod, darkness) upon de novo differentiation of tracheary elements (TEs) in callus derived from mature embryos of pepper cv. Bryza. Moreover, it was to determine the proliferation ability of the callus cells and changes of callus morphology. TEs were differentiated in the form of single cells, irregular clusters, strands and whirls exclusively with reticulate and pitted thickening of the secondary wall and the clusters occurred the most frequently. Cytokinin used alone, as well as in auxin combination, stimulated xylogenesis with the highest efficiency as well as with regard to the frequency and TE cell number within clusters. The highest number of TEs per cluster was obtained in the case of combination 0.1 mg·dm^-3 IAA + 0.1 mg·dm^-3 BAP on the light. Smooth surface, large cohesion cell degree and green colour are the morphological callus features accompanied by the effective TE formation.

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