ALTERATION OF THE AXIAL GRADIENT. 2IQ 



duced by KCN so that plants at this stage behave as if they 

 had already been subjected to KCN, and the final killing by 

 KCN is simply or largely additive to the changes which have 

 already occurred. The action of the ordinary narcotics such as 

 alcohol and ether, at least in its more advanced stages, and that 

 of KCN are also additive and thoroughly narcotized organisms 

 are more susceptible to KCN than normal organisms, though 

 there can be no question as to metabolic condition in the two 

 cases. Evidently changes in susceptibility produced by one 

 agent or condition can be made evident only by some agent or 

 condition whose effect is not strictly additive to the first. 



It seems not improbable that the present case is merely a 

 particular example of a general relation. In terms of the perme- 

 ability theory, for example, the first effect of an inhibiting 

 agent may be, or be associated with a decrease in permeability, 

 and if this effect is proportional to the original susceptibility 

 along the axis, it is not difficult to understand that one such 

 agent might produce a differential decrease in permeability and 

 so reverse the axial gradient in susceptibility to another. In 

 the later stages of the action of an inhibiting agent, there may 

 be on the other hand an increase in permeability resulting from 

 changes in protoplasmic aggregation or other changes, and after 

 this stage is reached the effect of one agent is essentially additive 

 to that of another. This is not to be regarded as a hypothesis 

 in the scientific sense to account for the facts, but rather as merely 

 a suggestion to illustrate how susceptibility relations may be 

 altered. This case also shows certain of the limitations and 

 difficulties of the susceptibility method in demonstrating by 

 means of one agent the effects of another. Some of these diffi- 

 culties may be removed or lessened by working with the proper 

 combinations of agents. 



For present purposes, however, the changes during the earlier, 

 not those of the later stages of confinement are important. 

 These changes, consisting in decrease in susceptibility and more 

 or less reversal of the general gradient, are the same as the 

 changes which occur very generally, though more slowly, under 

 laboratory conditions even in running water. There can be no 

 doubt that the transference of the plants from natural to labora- 



