CHEMICAL NATURE OF INDUCTIVE PROCESSES 413 



of the dark reaction, the hormone that has been synthesized is readily 

 destroyed by high temperature (Lockhart and Hamner, 1954). In 

 the light, provided this is of sufficient intensity, these immediate 

 products of the dark process are stabilized, converted to some material 

 insensitive to high temperature. This process runs its course in a 

 period of about 5 hr. Finally, translocation of the finished hormone 

 from the leaf occurs. Translocation out of the leaf starts roughly 20 hr 

 after the beginning of the dark period and completes its course 

 perhaps 48 hr after the beginning of the dark period (Salisbury, 1955; 

 Lockhart and Hamner, 1954). It is an interesting coincidence that 

 the first visible signs of floral differentiation in the growing point 

 occur at about the same time that translocation from the leaf is 

 completed. 



We have, then, an excellent and detailed description of the catenary 

 series of events which lead to the ultimate manifestation of floral 

 differentiation. All that we need to do is to put chemical names to the 

 individual substances described in physiological terms above. This 

 cannot be rigorously done. Let us see, however, what we can conclude 

 about the chemistry of hormone production in the leaf. One might 

 first ask: Is the floral hormone produced in the leaf identical with 

 gibberellic acid? This is a sensible question since we know that applica- 

 tions of gibberellic acid will replace photoperiodic induction in certain 

 long-day plants (Lang, 1956). Such applications will not, however, 

 replace photoperiodic induction in short-day plants such as Xanthium. 

 Gibberellic acid cannot therefore be the true flowering hormone since 

 it is a criterion of this material that it must be effective both in long- 

 and short-day forms. This follows from the fact that reciprocal graft- 

 ing experiments have shown that long-day plants on long days produce 

 material which causes flowering of short-day plants on long days, and 

 vice versa (Lang, 1952). Similarly one might ask: Is the flowering 

 hormone merely an antiauxin? Auxins inhibit flowering of short-day 

 plants (Bonner and Thurlow, 1949). Antiauxins promote flowering of 

 short-day plants, and in fact it has been shown to be possible to induce 

 flowering in short-day plants, under conditions in which such flower- 

 ing will not otherwise take place, by application of specific antiauxins 

 (Bonner, 1949). The answer to this question is a clear-cut no. It has 

 indeed been shown by Liverman and Lang (1956a) that antiauxins, 



