23O C. M. CHILD. 



were present, the new apical cell arises from the region of highest 

 susceptibility in the old cell. In the more advanced stages of 

 development in the Osterhout culture most of the cases in which 

 the susceptibility gradients were determined show the same 

 relations, but some exceptions occur, apparently in cases which 

 are in poor condition or gradually dying. Moreover, the fact 

 that in these isolated cells new apical cells arise more frequently 

 from the basal end or from both ends of the old cell than from 

 the apical end alone is undoubtedly connected with the fact 

 that cell separation is associated with obliteration or reversal 

 of the original axial gradient in the cells. The greater frequency 

 of development of new apical cells at or near one or both ends 

 of the old cell than in the middle region is probably also an 

 expression of gradient relations. Where the intracellular gradi- 

 ent was primarily basipetal and is completely reversed, the basal 

 end of the cell becomes physiologically apical, and morphological 

 development follows the new metabolic relations. Where the 

 original gradient is largely obliterated, the two ends of the 

 cell which were the regions of connection with other cells are 

 doubtless more affected than other parts of the cell by the change 

 in conditions accompanying the separation and undergo a certain 

 amount of regression and rejuvenescence, and so attain a higher 

 metabolic rate (Child, '150, Chap. X.). It is also possible that 

 in some cells from the more basal regions, where secondary basal 

 elongation is occurring, and where two opposed intracellular 

 gradients are often present (see p. 215) before separation, the 

 obliteration of these gradients is not complete at the time of 

 separation, and the higher rate at the two ends is still further 

 increased by separation, so that both ends become physiologically 

 apical. And finally, where the gradient is reversed in the 

 normal plant, as sometimes in the more basal cells, it may be 

 again reversed, obliterated or almost obliterated at the time of 

 separation with correspondingly different results in later develop- 

 ment. 



While it is impossible to follow the changes in the gradient 

 in a particular cell and to correlate them with the later develop- 

 ment, the high degree of constancy in the relation between the 

 intracellular gradients and the localization of the new axes leaves 



