QUANTITATIVE LAWS IN REGENERATION. II. 



By JACQUES LOEB. 

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



(Received for publication, May 21, 1920.) 

 I. 



In a preceding paper^ it has been shown that, when a piece of stem 

 inhibits the production of roots and shoots in a leaf of Bryophyllum 

 calycinum connected with it, the stem gains in mass and this mass 

 equals approximately the mass of shoots and roots the leaf would 

 have produced if it had been detached from the stem. On the basis 

 of this fact it was suggested that the inhibitory influence of the stem 

 upon the formation of roots and shoots in the leaf is due to the fact 

 that the material available for this process naturally flows into the 

 stem. 



In these experiments the quantity of roots formed had not been 

 measured directly but had been calculated on the assumption that 

 the dry weight of the roots formed is on the average 42 per cent of 

 the dry weight of the shoots formed in the same leaves. Since this 

 experiment seems to be crucial for the answer to the question why 

 the leaf does not form shoots or roots as long as it forms a part of a 

 normal plant it seemed advisable to make a direct determination of 

 the mass of roots formed by an isolated leaf. Five new sets of ex- 

 periments, as a rule with eight pairs of sister leaves, were made. The 

 method was the same as that described in the first paper.^ Table I 

 gives the dry weight of the organs. The experiments lasted about 

 1 month; if they last too short a time the error in measuring vitiates 

 the result and if we wait too long another complication arises inas- 

 much as the leaves of the shoots formed become too large and con- 

 tribute too much material for further growth and regeneration. 



1 Loeb, J., /. Gen. Physiol, 1919-20, ii, 297. 



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