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 a*s 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 



