When young stems are wounded or grafted so that the cambium is interrupted, new vascular cambia tend to regenerate in the callus proliferating from the wounded surfaces. The position in which such cambia arise varies according to the type of wound, but usually is such as to restore locally the normal condition of a closed cambial cylinder. Two theories have hitherto been proposed to define how the positions of these regenerating cambia are controlled. This paper presents evidence that neither of these theories is valid in all situations, and proposes a new working hypothesis. This ‘gradient induction’ hypothesis is stated at the end of the paper. It is in agreement with all types of wound and graft so far studied, and seems also to extend to cambium formation in tissue culture and perhaps to procambium formation in normal apices.
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