THE LAW CONTROLLING THE QUANTITY OF REGENERA- 

 TION IN THE STEM OF BRYOPHYLLUM CALYCINUM. 



By JACQUES LOEB. 



(From the Laboratories of The Rockefeller Institute for Medical Research) 



(Received for publication, June 24, 1918.) 

 I. 



It is well known that isolated pieces of plants and lower animals are 

 able to replace the lost parts by a new growth which is called regenera- 

 tion. The investigation of this phenomenon by merely qualitative 

 methods of experimentation has led only to verbahsms. Thus it 

 has been stated by Noll that the plant or animal possesses a "morph- 

 estesia;" i.e., a consciousness of what its proper form should be and 

 hence the regeneration of lost organs. Driesch applies a similar 

 verbalism calling the morphestesia ''entelechy." Weismann sug- 

 gests that without the power of regeneration many species might have 

 died out — hence regeneration. Others speak of regeneration as the 

 effect of the "stimulus" of the wound. If we wish to substitute for 

 these or similar expressions, which have led and can lead to no scientific 

 result, a theory in the sense in which this word is used by the physicist, 

 we must investigate the problem of regeneration by the methods of 

 quantitative experimentation. 



The writer has introduced such a method in the study of regenera- 

 tion of the plant Bryophyllum calycinum, which is unusually favorable 

 for work of this kind, and he has already reported some of the results 

 obtained. The most significant fact was found in the regeneration of 

 the leaf of this plant. When the leaf of Bryophyllum is detached 

 from the plant, it will form roots and shoots in its notches. Each 

 node of the stem has two leaves in opposite position — sister leaves 

 — which under normal conditions have equal size. Since they have 

 also the same age and the same history, they possess not only the same 

 mass but contain also very probably chloroplasts in the same number 

 and in the same degree of efficiency; so we can say such sister leaves 



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