96 REGENERATION OF BRYOPHYLLUM CALYCINUM 



growth of the regenerating shoot occurs at the expense of material 

 furnished by the basal leaf. 



4. This assumption is supported by two facts: first, that in the dark 

 this influence of the leaf disappears more or less completely; and, 

 second, that a leaf attached to the base of a regenerating stem after 

 some time weighs markedly less than does a sister leaf completely 

 detached from the stem, but otherwise under equal conditions. 



5. This latter fact that a leaf when attached to the base of an 

 excised piece of stem wilts more rapidly than when completely iso- 

 lated is the reason that the proportionality between mass of a basal 

 leaf and mass of shoot regenerated at the apex of an isolated piece of 

 stem cannot always be demonstrated with the same degree of accuracy 

 as the proportionality between the mass of completely isolated leaves 

 and the mass of shoots they produce. 



6. The material furnished by the leaf to the stem is nqt restricted to 

 water but includes also the solutes, since not only the fresh weight but 

 also the dry weight of the shoot regenerated by a piece of stem in- 

 creases with the mass of the leaf attached to the base of the stem; 

 and since not only the water contents but the dry weight of a leaf 

 attached to the base of an excised piece of stem diminish when com- 

 pared with the dry weight of a completely detached sister leaf. 



7. The mass of shoots produced by an isolated piece of stem without 

 leaf is small and almost negligible compared with the mass of shoots 

 produced by the same piece of stem when a leaf of sufficient mass is 

 attached to the base of the stem. 



