94 REGENERATION OF BRYOPHYLLUM CALYCINUM 



experiment.^ They leave no doubt of the fact that the basal leaf gives 

 off a considerable amount of its material to the stem. 



We have, therefore, a right to conclude that a basal leaf gives off 

 material to the stem, part of which is used for the formation of shoots 

 in the stem. 



Experiments were carried on in the dark and it was found that 

 the mass of shoots regenerated under these conditions was small even 

 when a large basal leaf was attached to the stem ; and no proportion- 

 ality between mass of leaf and of shoots regenerated on the stem 

 could be found. This indicates that the products of assimilation in 

 the leaf are part of the material used for the regeneration of the shoots 

 on the stem. 



TJicorctical Rouarks. 



These experiments have shown that in the case of the regeneration 

 of the leaf as well as of the stem the quantity of regeneration is 

 determined by the mass of material sent out by the leaf and manu- 

 factured in the leaf; and possibly also to a small extent by material 

 manufactured in the stem or circulating or stored in the stem at the 

 time the stem was cut out from the plant. 



The same simple mass law seems to hold for the quantity of roots 

 regenerated at the basal end of the stem or basally from a leaf attached 

 to the stem. It was very obvious in all our experiments that the mass 

 of roots formed in a piece of stem in a given time increases with the 

 mass of a leaf and the roots commence to grow out later when the leaf 

 is smaller. The writer has, however, not yet made enough quantita- 

 tive measurements to permit him to state that there is a strict propor- 

 tionality between mass of leaf and mass of roots regenerated. 

 r In animals the blood and lymph play the same role as does the sap 

 in plants, and we may surmise that the quantity of sugar, amino- 

 acids, salts, and of "accessory substances" in the body fluids determines 

 the quantity of regeneration in animals. In an animal, regeneration 

 may occur even when no food is taken up, and it is to be assumed that 

 the tissues of a fasting organism constantly convert some of the 

 material stored in the cells into sugar, amino-acids, and vitamines, 



^ We will omit these experiments here since they will be discussed in one of the 

 following papers. 



