THE RANGE OF DOMINANCE 155 



around the main stem and grow outward from the trunk, 

 and the branches of the second order arise in most cases 

 more or less bilaterally on them. Removal of the main 

 growing tip is followed by the bending upward of one or 

 more of the uppermost lateral branches, further growth 

 in the vertical direction, and radial instead of bilateral 

 outgrowth of new branches. Here one or more of the 

 lateral branches nearest the upper end of the stem 

 react to the absence of the main growing tip by changing 

 direction and form of growth to that characteristic of the 

 original tip. If this branch is removed, branches farther 

 down the trunk react in the same way. 



According to most authorities, dominance of one 

 part over another is effective only or chiefly in one 

 direction along the stem, namely, from the apical end 

 downward. Buds or growing tips at or nearer the 

 apical end are capable of inhibiting buds farther down 

 the stem, but the latter are not capable or are less 

 capable of inhibiting the former. In recent experi- 

 mentation,^ however, it has been demonstrated that 

 these relations may be reversed, and that if shoots lower 

 down are allowed to grow for a long enough time and to a 

 large enough size, while buds higher up are inhibited 

 by artificial means, the lower shoots sooner or later 

 acquire the ability to inhibit the higher ones after the 

 removal of the artificial inhibition. This is what 

 might be expected if inhibition depends on the relations 

 of metabolic gradients. Under ordinary conditions 

 the upper levels of the stem represent higher levels in 

 the gradient and therefore inhibit or obHterate gradients 



* W. Mogk, " Untersuchungen iiber Korrelationen von Knospen 

 und Sprossen," Archiv fur Entwickelungsmechanik, XXXVIII, 19 14. 



