AXIAL SUSCEPTIBILITY GRADIENTS IN ALG/E. 439 



a continuous mass of protoplasm very considerable local, or in 

 this case axial, differences in physiological condition and meta- 

 bolic activity may exist. 



In conclusion, the essential similarity of animals and plants in 

 respect to these axial susceptibility gradients may once more be 

 emphasized. The physiological axis is fundamentally the same 

 as regards susceptibility relations in both groups and undergoes 



very similar alterations. 



SUMMARY. 



1. The thalli of all axiate algae examined show an axial gradient 

 in susceptibility to various agents, KCN, alcohol, ether, HC1, 

 HgClo, CuSC>4, neutral red, high temperature, etc. To concentra- 

 tions or intensities sufficient to kill rapidly without acclimation 

 the apical region is most susceptible, and the susceptibility 

 decreases basipetally in each axis. This susceptibility gradient 

 may undergo more or less complete reversal under various condi- 

 tions. Certain concentrations of certain agents may even reverse 

 the gradient in susceptibility to themselves. 



2. As in animals the susceptibility gradient is in general an 

 indicator of the vitality, metabolic rate, or physiological condi- 

 tion at different levels of the axis. The gradient may be altered 

 or more or less completely reversed by change in external condi- 

 tions, by advancing age, by physiological isolation of parts, etc., 

 and the readiness with which alterations occur in altered environ- 

 ment is in some degree a measure of the sensitiveness of the 

 species. 



HULL ZOOLOGICAL LABORATORY, 

 UNIVERSITY OF CHICAGO, 

 November, 1916. 



REFERENCES. 

 Child, C. M. 



'i3a Studies on the Dynamics of Morphogenesis and Inheritance in Experi- 

 mental Reproduction. V., The Relation Between Resistance to Depress- 

 ing Agents and Rate of Reaction in Planaria dorotocephala and its Value 

 as a Method of Investigation. Jour. Exp. Zool., XIV. 



'i3b Studies, etc. VI., The Nature of the Axial Gradients in Planaria and 

 their Relation to Antero-posterior Dominance, Polarity and Symmetry. 

 Arch. f. Entwickelungsmech., XXXVII. 

 '14 The Axial Gradient in Ciliate Infusoria. BIOL. BULL., XXVI. 



Axial Gradients in the Early Development of the Starfish. Amer. Jour. 

 Physiol., XXXVII. 



