262 Pub. Puget Sound Biol. Sta. Vol. 2, No. 48 



the rate of growth and division decrease basipetally from the apical region, 

 a difference in electric potential must unquestionably also exist between the 

 apical and other levels. This difference in potential may constitute the basis 

 for a transmission relation between the apical and other levels of the axis. 

 And third, even though protoplasmic continuity from diatom to diatom pre- 

 sumably does not exist, there is continuity of the gelatinous envelope which 

 is a colloid, and it is quite possible that transmission of some electrolytic 

 cliange resulting from the difference of potential between the tip and other 

 levels, may occur in it. R. S. Lillie's experiments (Lillie, 1917, 1918) 

 with electrolytic gradients and electrolytic transmission in metals and his 

 discussion of their significance for a conception of protoplasmic transmis- 

 sion may be referred to in this connection. The difference in potential 

 along the axis may readily give rise to effects which constitute a factor in 

 determining physiological condition of the diatoms at different levels, at 

 least within a certain distance from the tip. At present it seems probable 

 in the light of all the facts that some such physiological correlation exists 

 in these pseudothalli and that their definiteness of growth-form is dependent 

 upon it, in short, that they are to some extent physiologically as well as 

 morphologically axes. 



Conclusion 



The facts presented above, together with many others recorded in 

 earlier papers, leave no doubt that the difference in susceptibility observed 

 at different levels of a single axis and in different axes of the same plant 

 are in some way associated with differences in physiological condition of 

 some sort. In axes of the usual kind, with the chief growing region at the 

 apical end the gradient in susceptibility along the axis evidently corresponds 

 to a gradient in growth activity, and in Nereocystis, in which the chief 

 growing region of the stipe is apical and that of the frond basal, the corre- 

 spondence between growth and suceptibility still holds. Moreover, in thalli 

 with branching growth-form of definite type, the differences in susceptibility 

 in different axes correspond to the relations of those axes to the general 

 growth-form. ^'*'***!». v . 



In animals it has been found that susceptibility to killing concentration's' 

 of various agents varies in general with the degree, intensity or rate of 

 metabolic activity. There is good reason to believe that in animals the oxida- 

 tions are fundamental reactions in the metabolic complex, and, so far as data 

 are at hand, we find evidence that a general relation exists between suscep- 

 tibility and rate of oxidation. Whether this relation will prove to be uni- 

 versal or not can be determined only by future investigation, but on the 

 basis of our present knowledge, susceptibility appears to be in some way 

 associated with the rate of fundamental reactions. 



