Experiments on growth and inhibition. Part III—Inhibition and growth promotion

Abstract

The question is raised why, in dicots, the growing leaves of a shoot tend in general to inhibit lateral buds or shoots, but promote the growth of their own shoot below them. The difference is not directly due to the fact that the lateral buds or shoots are differently orientated with regard to the influence reaching them from the growing leaves of the dominant shoot. In Vicia faba strips of mature stem that are out of the line between growing leaves and roots survive and grow in thickness if they are attached by the top, so that they receive the downward-moving cambial stimulus; but if attached by the base, they die. Also strips of very young internodes, attached by the top only, elongate rapidly. The fact that the stems of growing shoots are in the line between growing leaves and roots is only of subordinate importance, for parts of stem that are in this line make no cambial growth unless they receive the cambial stimulus, though they survive much longer than similar parts that are not in this line. It is concluded that the stems of growing shoots are protected from the inhibiting influence by the cambial stimulus and other growth-promoting influences coming from their own growing leaves.