THE CHEMICAL MECHANISM OF REGENERATION 3 



Whileit was thus possible to show in lliis and in other cases 

 that the observations on régénération in animais agrée with 

 a chemical theory of régénération, an adéquate proof was 

 lacking ; since for this purpose quantitative déterminations 

 were required. The fact that the spécifie organ-forming sub- 

 stances of Sachs were unknown and the statement that they 

 exist only in minute traces in an organism made it appear a 

 hopeless task to undertake quantitative experiments. The 

 writer has recently found that we can investigate the régéné- 

 ration of the tropical plant Bryophylliun calycinum by quanti- 

 tative methods without having recourse to ihe hypothetical 

 organ-forming substances of Sachs (1). 



2. — The leaves of this plant possess the peculiarity of 

 containing dormant buds in each of their notches (fig. 2) which 

 give rise to roots and shoots as soon as the leaf is separaled from 

 the plant, or about to fall ofF. An explanalion of the mecha- 

 nism of this « régénération » must also explain the mechanism 

 by which the régénération is inhibited as long as the leaf is in 

 connection with the whole plant. We shall try to show in this 

 paper that régénération or rather the growlh of the dormant 

 buds in the isoiated leaf of Brijophyllum takes place as a consé- 

 quence of the mass action of substances présent, or formed in 

 the leaf ; and Ihat this régénération cannot take place as long as 

 the leaf is part of the plant, because the substances needed for 

 « régénération » in the leaf flow into the stem of the plant. 

 The writer has found a quantitative method by which this idea 

 can be tested. 



When a leaf of Bryophyllum calycinum is separated from its 

 plant it produces new shoots, not in ail of ils notches but in 

 only a few; while when the leaf is eut into as many pièces as it 

 contains notches, each notch will give rise to a new shoot. 

 Hence we may ask the question, why do not ail the notches 

 grow out in an isoiated leaf when it is not eut into pièces? 

 It is obvious that hère we are confronted with the problem of 

 inhibition of régénération in so simple a form that a definite 

 solution can be found. 



(1) J. LoEB, Science, 1917, XLV, 436; XLVI, 115. 



