FURTHER OBSERVATIONS ON AXIAL SUSCEPTI- 

 BILITY GRADIENTS IN ALG&. 



C. M. CHILD. 



WITH TWO FIGURES. 



INTRODUCTORY. 



In a recent paper (Child, ! i6a) it was shown that axial gradients 

 in susceptibility to cyanides and various other agents are char- 

 acteristic features of some fourteen species of axiate marine algee, 

 and the question of the significance of these gradients in relation 

 to polarity and developmental order was considered. 



The present paper records observations made during the 

 summer of 1916 at the Marine Biological Laboratory, Woods 

 Hole. It is concerned primarily with the demonstration of what 

 may be called the normal gradients in the species examined, 

 i. e., the gradients characteristic of the plant in good physiological 

 condition under good or average rather than extreme, environ- 

 mental conditions, but some of the alterations resulting from 

 altered environment are briefly described. In addition to the 

 fourteen species of the earlier paper, eleven more species have 

 been examined, at least in part, with definite results in every case. 



The method used is essentially the same that was employed 

 to demonstrate the axial gradients in various other animal and 

 plant species (Child, '136, '14, '150, '15^, Chap. III., 'i6a, '166). 

 It consists in determining the susceptibility to, i. e., the survival 

 time in, a certain concentration of an agent which kills within 

 a few hours, but not immediately. The differences in suscepti- 

 bility as determined by the differences in survival-time along 

 an axis or in different organs are in general an indication of the 

 differences in physiological condition. The relations between 

 susceptibility to inhibiting agents and physiological, metabolic 

 or protoplasmic condition have been discussed elsewhere (Child, 

 '13^, '156, Chap. III., 'i6a) and require no further consideration 

 at present. 



The time of death of the plant cells is approximately deter- 



419 



