THE RANGE OF DOMINANCE 



167 



gradient. Because of the relatively high metabolic level 

 of these cells along the midrib this region plays a more 

 important part in the localization of reproduction than 

 the median region in Planaria. In fact, the experi- 

 mental evidence seems to indicate that the chief differ- 

 ence in axial relations between Marchantia and Planaria 

 is the higher metabolic level of the apical region of the 

 transverse gradient, the median region of the body. 



FIGS. 99-102. Localization of new individual as resultant of differ- 

 ent axial gradients in pieces of liverwort, Marchantia: Fig. 99, usual 

 position in median ventral region near apical end of piece; Figs. 100- 

 102, different positions of new individual apparently determined by the 

 different relations of the axial gradients according to shape of piece 

 and region represented (from Vochting). 



With advancing age the region of the midrib undergoes 

 gradual differentiation and so loses to a greater or less 

 extent its high metabolic rate. 



These experiments and many others which cannot be 

 discussed here are highly significant in that they indi- 

 cate the essential identity in character of the different 

 axes of the physiological individual. In fact, I believe 

 they constitute evidence of the greatest importance 



