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BOTANICAL GAZETTE 



[OCTOBER 



and other papers it has also been maintained on the basis of various 

 lines of evidence that this relation originates in a difference in 

 rate of fundamental metabolic reactions, such differences of course 

 being associated with differences in protoplasmic condition. 

 These differences appear in the form of gradations in physiological 

 condition, which have been called metabolic or physiological 

 gradients. Since a discussion of the nature and origin of these 

 gradients and the evidence on which the conclusions are based 

 has recently appeared (Child 6), extended discussion of these 

 matters is not necessary at this time. In such a physiological 

 gradient the dominant region is primarily the region of highest 

 metabolic* rate, of greatest physiological activity. The evidence 

 indicates further that the relation between dominant and subordi- 

 nate parts is primarily transmissive, rather than transportative in 

 character; that is, that the dominance of a particular part is 

 primarily dependent upon dynamic changes transmitted from it 

 to other parts, rather than upon the transportation from the 

 one part to the other of substances in mass. Since this dynamic 

 effect of a region of high metabolic rate upon other parts is a factor 

 in determining the metabolic rate of the parts affected, and since 

 in protoplasm without highly specialized conducting paths it 

 decreases with increasing distance from the region of high rate, 

 the result of the establishment of such a region of high rate, how- 

 ever brought about, is the development of a more or less definite 

 physiological gradient. The physiological axis in its simplest 

 terms is such a gradient, determined in relation to a region of 

 high activity which is the dominant region of the axis. 



It has been found, largely through the work of Hyman and 

 Bellamy, which is not yet published, that gradients in electrical 

 potential and electric currents resulting from them are character- 

 istic features of these physiological gradients. Discussion of the 

 significance of these bioelectric currents is impossible here, but 

 many facts make it highly probable that they are the factors 

 primarily concerned in transmission of excitation (Lillie 8-13), 

 and that they play a fundamental part in determining and main- 

 taining the physiological gradients which arise in relation to 

 regions of high metabolic rate. If this is true, the dominance of 





