THE PHYSIOLOGICAL BASIS OF MORPHOLOGICAL 

 POLARITY IN REGENERATION. I. 



By JACQUES LOEB. 



(From the Laboratories of TheRockefeller Institute for Medical Research.) 



(Received for publication, November 21, 1918.) 

 INTRODUCTION. 



In two preceding papers^ on regeneration in Bryophyllum calycinum 

 it had been shown that the mass of shoots formed in a leaf or in a 

 piece of stem to the base of which a leaf is attached increases with the 

 mass of the leaf. This proves that regeneration is a phenomenon of 

 the order of nutrition and growth. 



The question arises how this conclusion harmonizes with the well 

 known fact of the polar character of regeneration. When we cut out a 

 piece from a higher plant or a lower animal the piece regenerates, as a 

 rule, a shoot or head at the apical end and roots or a tail at the 

 basal end. In a preliminary paper,^ published a year ago, the writer 

 described experiments suggesting that the polar character of regenera- 

 tion might be due to the existence in the circulating sap (or lymph 

 and blood) of inhibitory substances which prevent dormant buds or 

 resting cells from growing out even if an adequate quantity of food- 

 stuffs is available. It was shown by experiments on Bryophyllum 

 calycinum that the leaves as well as the growing shoots have an in- 

 hibitory influence upon the growth of all the dormant buds situated 

 more basally in the stem. If we assume that these inhibitory influ- 

 ences are due to certain constituents in the sap sent out by growing 

 buds and by leaves, we come to the following theory of the polar 

 character of regeneration. When we cut out a piece of stem from 

 Bryophyllum and remove all the leaves, inhibitory substances will 

 continue to flow in a basal direction in the stem. Since the apical 



^Loeb, J., Bot. Gaz., 1918, Ixv, 150; /. Gen. Physiol., 1918, i, 81. 

 ^ Loeb, Science, 1917, xlvi, 547. 



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