82 REGENERATION OF BRYOPHYLLUM CALYCINUM 



have approximately equal masses of active substance. The writer was 

 able to show that such sister leaves of equal weight produce equal masses 

 of shoots in equal times and under equal conditions of illumination, 

 temperature, and moisture. He found, moreover, that if we reduce the 

 mass of one set of sister leaves by cutting out pieces from the center 

 of the leaves, while the other set remains intact, both sets produce 

 shoots approximately in proportion to their masses, even if the number 

 of shoots produced by the two sets differs widely. We, therefore, can 

 say that equal masses of sister leaves produce equal masses of shoots in 

 equal times and under equal conditions, regardless of the number of shoots 

 produced} 



This law shows that the problem of regeneration is part of the prob- 

 lem of growth and that it falls under the law of chemical mass action. 



Inasmuch as age and previous history influence the active mass of 

 photosynthetic material of the leaf, it is obvious that the law of the 

 production of equal masses of shoots by equal masses of leaves is 

 fulfilled more accurately by comparing sister leaves than it would be 

 by comparing leaves with a different history; i.e., leaves which differ 

 in the mass of photosynthetic material in the unit mass of leaf. In 

 such cases we should have to use statistical methods; i.e., we should be 

 compelled to use much larger numbers of leaves in order to eliminate 

 the influence of variation in the relative mass of photosynthetic and 

 other material in the leaf which is required for the regeneration 

 (growth) of the shoots. 



II. 



Regeneration in an isolated piece of stem is much more general than 

 regeneration in an isolated leaf, and the question arises whether a 

 similar mass law, as that found for regeneration in a leaf, controls 

 the quantity of regeneration in a stem. 



In the axil of each leaf of the stem of Bryophyllum is found a dor- 

 mant bud capable of growing into a shoot (3, Fig. 1). Each node 

 contains two such dormant buds on opposite sides, one in the axil 

 of each leaf. In successive nodes the lines connecting the two leaves 



^ Loeb, J., Science, 19X1 , xlv, 436; Bot. Gaz., 1918, Ixv, 150; ^;/«. Inst. Pasteur, 

 1918, xxxii, 1. 



