vi PREFACE 



measurements was made, the measurements led to no rationalistic 

 correlation between the process of regeneration and the mutila- 

 tion of the organism, for the reason that there was no clear 

 conception concerning the quantity which it was necessary to 

 measure.^ This is only possible if we have a clear idea of the 

 physico-chemical relation which it is intended or necessary to 

 test. 



The writer has for a number of years conducted quantitative 

 experiments on the regeneration of a plant, BryophyUum caly- 

 cinum, which have made it possible to correlate the process of 

 regeneration with the quantity of chemical material. By compar- 

 ing the dry weight of the regenerated shoots and roots with the 

 dry weight of the leaves or stems which were used for regenera- 

 tion, it could be shown that in the presence of Hght the quantity 

 of regeneration was under equal conditions of illumination, 

 temperature, and in equal time in direct proportion to the mass 

 of the leaves or stems from which regeneration started. If we 

 make the legitimate assumption that the material required for 

 the formation of new shoots or roots was under the conditions of 

 our experiments produced by the chlorophyll contained in the 

 leaf or stem, it follows that the quantity of regeneration is deter- 

 mined in this case by the mass of material available in the stem 

 or leaf for synthetic processes. Under the guidance of this mass 

 relation (which may be, in part at least, identical with the law of 

 mass action), it could be shown that mutilation of the plant leads 

 to a collection of sap in places where it would not have collected 

 without the mutilation. This accounts for the fact that mutila- 

 tion leads to growth in places of the organism where no growth 

 would have occurred without mutilation. The process of 

 regeneration was thus revealed as a purely physico-chemical 



1 In addition to the literature mentioned in the text, the reader is referred 

 to Barfurth, D., Methoden zur Erforschung der Regeneration bei Tieren, in 

 Abderhalden's Handh. biol. Arbeitsmeth., Abt. V, Teil 3, Heft 1, 1921, and 

 Barfurth's and Driesch's reviews of the literature in Ergeb. Anatnm. 

 XI. Entivicklungsgesch., Vol. xxii, 1914, and earlier volumes. Also Korschelt, 

 E., Regeneration und Transplantation, Jena, 1907; Przibram, H., Experimen- 

 tal-Zoologie, ii, Regeneration, Leipzig and Wien, 1909. The most interesting 

 recent publications on regeneration are from Przibram's laboratory, by him- 

 self and his collaborators. For the problem of growth which is fundamental 

 for regeneration, the reader is referred to Robertson, T. B., "The Chemical 

 Basis of Growth and Secenscence, Philadelphia and London, 1923. 



