The Time Course of Sieve Tube and Xylem Cell Regeneration and Their Anatomical Orientation in Coleus Stems

Study of the time course of regeneration around a wound in internode number 5 of Coleus showed that first recognizable developing sieve tubes appear 2 days after wounding. Xylem cells appear 3 days after wounding in intact plants and 2 days after wounding in isolated internodes and internode stumps. Xylem cells regenerate on the same radii with previously existing sieve tubes. Separation of xylem from phloem by a cover slip in the cambial zone at the beginning of the experimental period resulted in formation of radially aligned xylem cells and sieve‐tube strands on the phloem side of the cover slip. The results indicate that IAA moves basipetally in the phloem or cambium. The relationship between causal factors in normal vascular differentiation and in the regenerating vascular system is discussed.