Root Formation in Pea Cuttings III.

Cuttings were either decapitated or both decapitated and disbudded at different time intervals. Cytokinin, at different concentrations, was applied to the cuttings in lanoline. Higher concentrations of cytokinin inhibited root initiation during the early stage. However, the inhibitory effect of cytokinin disappeared during the later stage of root initiation. Lower concentrations of cytokinin promoted the root initiation during the early stage. This effect was observed on cuttings which were only decapitated. These results seem to indicate that the influence of cytokinin changes with the stage of development. There seems to be an interaction between cytokinin and one or more other growth factors. A possible reason for this may be that cytokinin, in higher concentrations, produces inhibitory effects during the early part of root initiation by blocking the activity of auxin. The loss of the inhibitory effect of cytokinin during the later part of the initiation phase suggests that, at this stage, developing root primordia are capable of controlling the level of active cytokinin and thus do not react to the exogenous application of cytokinin.