224 C. M - CHILD. 



complete obliteration. It may be also that in some cells, where 

 the original gradient had undergone reversal in connection with 

 the basal growth, another reversal may accompany cell separa- 

 tion. 



Fig. 6 shows a case in which a new polarity at right angles to 

 the old appears in the basal region of a large cell. A new axis 

 consisting of an apical and a subapical cell, has arisen from the 

 lateral cell-surface near the basal end. The susceptibility 

 gradient was not determined in this case, but there can be no 

 doubt that the new axis represents a new gradient. The gradient 

 in this case may perhaps have been directly determined by the 

 differential action of an external factor, possibly concentration of 

 oxygen or other substances necessary for metabolism. Cells 

 lying on the bottom of the dish, or perhaps in contact with other 

 cells, may often be subjected to such an external differential, 

 and where the original gradient is to a large extent obliterated, a 

 new gradient, and so a new axis may readily arise. Cases of 

 this sort have been recorded for Corymorpha, among the lower 

 animals (Child, '156, pp. 142-146). 



Unfortunately this culture of Griffithsia was made toward the 

 end of the season, and my departure from Woods Hole prevented 

 long continued observation. Through the kindness of Professor 

 Osterhout, however, in turning over to me a culture of Griffithsia 

 which had been in the laboratory some three months in very 

 slowly running water, I was able to make some observations on 

 more advanced stages of development of isolated cells. In this 

 culture cell separation had occurred to a large extent, and many 

 isolated cells showed considerable growth, although at the time 

 of examination in many cases the new growths were dying or 

 not in good condition. Figs. 7-10 show cases from this culture 

 in which the susceptibility gradient was determined. 



In Fig. 7 a new two-celled axis has arisen from the basal end 

 of a cell, and the general susceptibility gradient, as indicated by 

 the arrow, shows the usual relation to this axis, but the intra- 

 cellular gradient in the large old cell is very slight. 



Fig. 8 shows another case of a new axis consisting of three cells 

 arising from the basal end of a large old cell and two new living 

 rhizoids on the basal half and one dead rhizoid, indicated by 



