Phloem differentiation in Coleus pith explants

A simple tissue culture protocol was used to examine phloem differentiation. Sieve tube elements differentiated from Coleus blumei Benth. pith parenchyma when pith blocks were explanted on to an agar medium containing sucrose and indole acetic acid. Growth regulator concentration had surprisingly little influence on the production of phloem cells. Increasing the availability of sucrose, however, resulted in an enhancement of phloem differentiation. Evidently phloem and xylem differentiation began at the same time in this system, and the concentration of sucrose determined the relative production of phloem cells.