ALTERATION OF THE AXIAL GRADIENT. 23! 



little room for doubt concerning the fundamental character of 

 the relation. 



The cases where the new axes arise from the lateral surface 

 rather than the end of the cell, as in Figs. 6, 13, 14, or from the 

 middle region, as in Fig. 15, cannot be definitely accounted for, 

 but are doubtless connected with special external conditions, 

 perhaps the position of the cell with respect to light, oxygen 

 supply or other external factors, or perhaps with local metabolic 

 differences in the cell produced in some other way. I believe, 

 however, that if we could analyze these cases, we should find 

 that they, like the others, are an expression of the existing 

 gradient relations, however these may have been determined 

 (cf. Tobler, '06). 



The localization of the rhizoids also agrees in general with 

 expectation as far as the data go. In general they arise from a 

 relatively low metabolic level on the cells, but this level may be 

 in the middle region (Fig. 9) or at or near one end (Figs. 5, 6, n), 

 or rhizoids may appear progressively over a considerable length 

 of the cell or cells (Figs. 8 and 12). 



As regards the facts of morphological development, these 

 experiments add nothing of fundamental importance to those 

 of Tobler ('02, '04, '06), but the determination of the relations 

 between the susceptibility gradients and cell separation and the 

 localization of new axes serves to throw some light on the physio- 

 logical conditions concerned in this development and on the prob- 

 lems of physiological polarity and physiological integration or 

 individuation. 



These experiments suggest further possibilities of more exact 

 control of the localization of new axes on isolated cells, such as 

 the determination of the influence of the direct subjection of 

 single cells to the differential action of external factors on the 



localization of new axes. 



SUMMARY. 



i. The original axial susceptibility gradient of the alga Grif- 

 fith si a is more or less completely obliterated or reversed after 

 one or two days of confinement in a small volume of water, and 

 the larger the volume of living plant protoplasm introduced, 

 the more rapid the changes. 



