CHEMICAL NATURE OF INDUCTIVE PROCESSES 419 



tween the flowering impulse sent out by a photoperiodically treated 

 leaf and the material sent out by the bud which has been transformed 

 as the result of the reception of such a flowering stimulus. It appears 

 possible that the mature leaf, in Xanthium at least, may itself never 

 become transformed in the sense of becoming permanently changed. 

 The permanent change, the transformation which we associate with the 

 induced state, may well take place only in buds in photoperiodic induc- 

 tion as it does in vernalization. 



Difficulties stand in the way of the hypothesis presented above. Thus, 

 a plant which has been photoperiodically induced may be removed 

 from the photoperiodically inductive condition, disbudded, and may 

 then continue to act as a donor of flowering stimulus in graft partner- 

 ship. This fact has been interpreted by Carr (1953) to mean that 

 active buds act to conserve, maintain, and stabilize the flowering stimu- 

 lus of the mature leaf. But it could also mean alternatively that in dis- 

 budded donor plants, the buds, while they were present, became trans- 

 formed, produced transforming principle, and then proceeded to fill 

 the tissues of the donor plant with the material. The correct interpreta- 

 tion of these active bud experiments remains to be assigned. There are 

 evident experiments to do. We should try to see whether we can dis- 

 tinguish physiologically between induction in the bud and perception 

 in the leaf. We might try to make this distinction with the aid of 

 metabolite antagonists. Preliminary experiments by Labouriau (1956) 

 have in fact indicated that inhibitors of RNA synthesis, although they 

 are inert in inhibition of the process of floral hormone synthesis in the 

 leaf, do nonetheless act powerfully to inhibit differentiation of the 

 vegetative bud into a floral bud. 



This discussion has been remarkable by virtue of the paucity of 

 chemical information which it contains. The chemical nature neither 

 of the signal for flowering transmitted from the leaf nor of the factor 

 responsible for transformation in the bud can be assigned. It has been 

 noted, however, here, and by many earlier workers, that induction ap- 

 pears to be self-perpetuative. We are accustomed today to think of 

 self-perpetuative processes of living things as being intimately associ- 

 ated with and referrable to nucleic acids or nucleoproteins. It is tempt- 

 ing, therefore, to wonder if the self-perpetuative aspects of photo- 

 periodic induction may not also have their basis in phenomena 



