PHYSIOLOGICAL DOMINANCE ioi 



gradients have not been determined, their character and 

 the conditions of their development indicate that when- 

 ever an apical structure arises it represents the apical 

 region of a metabolic gradient. 



In the plants also conditions are apparently similar. 

 The apical region of a plant individual may arise inde- 

 pendently of other parts, and if it becomes structurally 

 connected with them later the connection develops 

 progressively from the new apical region toward other 

 parts and not in the opposite direction. The formation 

 of buds on the leaves of begonia and in wound callus, 

 described above (pp. 83-86), are cases in point, and 

 many other sirnilar cases might be cited. The develop- 

 mental gradients in such cases indicate that the new 

 apical structure or part represents the apical region of a 

 metabolic gradient. 



These conclusions concerning the independence of the 

 apical region and its relation to the metabolic gradient, 

 which are based upon experimental demonstration for 

 certain cases and highly convincing evidence for others, 

 are in full agreement with the facts of embryonic develop- 

 ment. There also, so far as experimental evidence has 

 been obtained, the apical region of the individual is the 

 apical region of a metabolic gradient, and precedence 

 of the apical region in development and the develop- 

 mental gradients in the direction of the major axis 

 indicate that this relation is general. I believe 

 we are justified in concluding that in this respect 

 development of the organic individual is always and 

 everywhere the same. Further evidence in support 

 of this conclusion will be presented in the following 

 pages. 



