THEORY OF REGENERATION BASED ON MASS RELATION.* III . FURTItER EX.eER~ENTS ON THE CAUSE

I t had been stated in a preceding paper ~ that we have to decide between two possible explanations of the polar character of regeneration in the stem of Bryophyllum calycinum; namely, first, Sachs' idea that the polar character of regeneration in the stem is due to a difference in the chemical constitution of the ascending and descending sap, the ascending sap containing special shoot-forming substances collecting at the apex, the descending sap containing root-forming substances collecting at the base. The second possible explanation is that the anlagen for roots and shoots are contained in different histological elements of the stem and that the ascending sap reaches primarily the anlagen for shoot formation, while the descending sap reaches primarily the anlagen for root formation. This latter explana. tion does not exclude the possibility that there exist chemical differences between the ascending and descending sap; it only assumes that the chemical differences between ascending and descending sap which in all likelihood exist are not the cause of the polar character of regeneration in the stem.