Differentiation of isolated interfascicular tissue of Ricinus communis L.

From hypocotyls of 6, 7, or 8 days old castor bean seedlings which in situ start to develop an interfascicular cambium on the 11th or 12th day, strips of interfascicular tissue were separated from adjacent vascular tissue by means of radially inserted metal blades or were excised and cultured in a basal medium containing mineral salts and sucrose. Since under these conditions cambial development proceeded normally, it is concluded that the vascular tissue does not supply the parenchymatous cells of the interfascicular tissue with a specific inductive factor. Addition of IAA, GA3, or kinetin to the medium enhanced development. It is argued that this is not the consequence of chemical substitution for a stimulatory influence from the adjacent vascular tissue, but rather a compensation for (i) production of growth substances by the dividing cambial cells, partially leaking out under the conditions of the culture, or for (ii) stimulatory substances originating in vivo from the apical parts of the plants.