226 C. M. CHILD. 



rhizoid had arisen from the apical region before isolation (see 

 p. 215). After isolation the conditions determined a double 

 gradient, the old rhizoid died and new rhizoids arose in relation 

 to the new axis. The original apical end of the cell, although it 

 represents the high end of a gradient, is not active enough to give 

 rise to a new apical cell. 



Fig. 9 shows a cell with two new axes, one of four cells, the 

 other of one cell, at its original basal end, one new two-celled 

 axis at its apical end and a rhizoid arising from its middle region. 

 The gradients are indicated by the arrows. It will be observed 

 that a double gradient exists in the old cell, the middle region, 

 where the rhizoid arises, being the region of lowest susceptibility. 

 The two axes at the basal end and also the rhizoid were found to 

 be more susceptible than the new axis at the apical end of the 

 old cell, and the old cell is least susceptible of all, and its middle 

 region the least susceptible region. 



Fig. 10 is another case with new axes at both ends of the old 

 cell. At the original apical end is one three-celled axis with 

 two one-celled branches and one rhizoid arising from its most 

 basal cell. At the original basal end of the old cell is another 

 axis of two cells and the old cell also bears a rhizoid near its 

 apical end. In this case observation of the progress of death 

 was interrupted, and the susceptibility gradients were observed 

 only in part. Those observed are indicated by arrows. This 

 case showed all indications of being in poor physiological con- 

 dition. The small apical cells were very heavily pigmented and 

 instead of being rounded were flattened basally, suggesting a 

 low turgor. The protoplasm of the large cell had also under- 

 gone structural changes similar to those which precede death in 

 KCN and other agents. The susceptibility of all the new 

 axes, except the one rhizoid axis arising from the old cell, was 

 somewhat lower than that of the old cell itself. In the absence 

 of knowledge of earlier stages in the life history of this case it is 

 impossible to determine the meaning of the susceptibility rela- 

 tions between new and old parts. In several other cases the new 

 axes were found to be less susceptible than the old cell, and in 

 every such case the new axis, or at least its apical cell was very 

 deeply pigmented and flattened basally, and the protoplasm of 



