CHEMICAL NATURE OF INDUCTIVE PROCESSES 415 



the floral stimulus from destruction; and in general the reaction ap- 

 pears to be determined by temperature alone and independent of other 

 external factors. Useful as this finding has been for characterization of 

 the physiology of induction, it has not helped us toward an understand- 

 ing of the chemistry involved. 



Auxin-induced destruction of the flowering hormone was first clearly 

 recognized by Lockhart and Hamner (1954) and by Salisbury 

 (1955). A plant is induced, say, with a 12-hr night. Auxin is now 

 added to the leaf, and the plant is allowed to remain in darkness for a 

 further 4 hr. It is now returned to light. It is found that those plants 

 which have received auxin at the end of the 12-hr dark period not only 

 flower more poorly than those to which auxin was not applied and 

 which received a 1 6-hr night period but also more poorly than plants 

 removed from dark at the end of 12 hr and returned to light. In the 

 present terminology this represents destruction of flowering stimulus. It 

 is a rapid effect since, as detailed above, the effect is readily detectable 

 over a reaction period as short as 4 hr. The inhibition is a real auxin 

 effect. Only compounds with the physiological effectiveness of auxin 

 are active; antiauxins inhibit the auxin-induced destruction; and, as 

 shown by Salisbury (1955), the auxin concentration dependence of 

 destruction of floral stimulus resembles in its hyperbolic form the auxin 

 concentration dependence of auxin-induced cell elongation. We ordi- 

 narily think of auxin-induced responses as positive ones. Auxin appears 

 to bring about chemical effects which cause cell walls to become more 

 plastic, for example. How can it cause a decrease in amount of floral 

 stimulus in the leaf? Initiation of the auxin-induced metabolism within 

 the tissue must apparently use up something which is needed for 

 maintenance of the flowering stimulus. More specific we cannot be. 

 Again, this phenomenon is not of great help to us in the elucidation of 

 the chemistry of the inductive process. 



The stabilization of the hormone during the first few hours in high- 

 intensity light at the end of the dark period has been detected and 

 estabhshed as a real phenomenon by Lockhart and Hamner (1954). 

 The floral stimulus, once stabilized by the action of high-intensity light, 

 is no longer subject to destruction either by high temperature or auxin. 

 It should be possible to characterize the light stabilization process. Is 

 it a photosynthesis-mediated process? Can the effect of high-intensity 



