ALTERATION OF THE AXIAL GRADIENT. 217 



environmental conditions. In these experiments masses con- 

 sisting of many axes were placed in 100 c.c. Erlenmeyer flasks 

 which were filled with water, corked without air space and 

 kept in the running water of the laboratory aquarium under the 

 same conditions of light and temperature as the stock. 



Susceptibility tests were made on the fresh material before 

 confinement, and at intervals during the experiment the sus- 

 ceptibility to KCN m/ioo or m/^o of portions removed from the 

 flask was compared with that of controls from the same plants 

 kept in running water, the phycoerythrin serving as indicator of 

 death, as described in an earlier paper (Child, 'i6e). 



The results of these experiments are briefly as follows: the 

 plants of course die in the flask in a few days at most, in my 

 experiments in 2-7 days, the survival time varying in general 

 inversely as the amount of plant tissue present. The death 

 gradient is basipetal as with other agents, i. e., the apical regions 

 are most susceptible to the confinement and the susceptibility 

 decreases basipetally. The progress of death can be observed 

 with the naked eye without difficulty, for each cell as it dies 

 becomes orange-yellow by reflected light. 



After twenty-four hours' confinement and before the death of 

 any cells the susceptibility to KCN has decreased and the general 

 susceptibility gradient in KCN shows a more or less complete 

 reversal in the apical regions of most axes. This reversal may 

 involve only the apical cell itself, in which case it dies later 

 instead of earlier than the cell next below it, or it may include 

 two, three or even the five or six most apical cells of the axis. 

 In such cases these cells are less susceptible and die later than 

 the cells next below, and in this group the death gradient from 

 cell to cell is more or less distinctly acropetal, the apical cell dying 

 last. Where the apical cell has recently divided and is very 

 small it may still show a high susceptibility and the reversal 

 may occur in the subapical region. 



After forty-eight to sixty hours' confinement the susceptibility 

 to KCN is usually again as high as or even considerably higher 

 than that of fresh plants and the gradient is in general again 

 basipetal. This increase in susceptibility and the reappearance 

 of the basipetal gradient in KCN is soon followed in my experi- 

 ments by the beginning of death in the apical regions. 



