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THE AMERICAN NATURALIST [Vol. XLII 



extended, till to speak of the evolution of societies, of 

 solar systems, or of chemical elements is now but com- 

 monplace. 



The biologist, with all his special difficulties, has at 

 least the limitation that he is only concerned with the 

 middle range of the interminable hostile front of natural 

 phenomena, and that for him is ordained the stubborn 

 direct attack, leaving the brilliant attempts at outflanking 

 movements to the astronomers on the one wing and the 

 workers at corpuscular emanations on the other. 



The atoms and molecules that the biologist has to deal 

 with do not differ from those passing by the same names 

 in the laboratories of chemistry and physics (at least no 

 one suggests this), and their study may therefore be left 

 to others. At the other end of the scale, with astronom- 

 ical magnitudes we have not to deal, unless indeed we 

 yield to the popular clamour to take over the canals on 

 Mars as phenomena necessarily of biological causation. 



In the study of that particular range of phenomena 

 which is the special allotment of the physiologists, animal 

 and vegetable, we have had ever before us the problem 

 of whether there is not here some discontinuity in nature; 

 whether the play of molecular and atomic forces occur- 

 ring outside the living organism can ever account for the 

 whole of the complexity and correlation of chemical and 

 physical interactions demonstrable within the living struc- 

 ture. 



As yet we are of course far from any answer to this 

 question, and no one in a scientific assembly like this will 

 call upon us for prophecies. Yet the subject to which 

 I shall devote my address has a bearing upon this ques- 

 tion. I propose to consider a particular aspect of the 

 relation of chemical changes in a test-tube to those taking 

 place in a living growing plant, and this in the spirit of 

 one who craves for continuity throughout natural phe- 

 nomena. 



The point of view from which the chemist regards the 

 reaction taking place in his test-tube has- undergone a 



