INFLUENCE OF GIBBERELLIC ACID ON THE 



FLOWERING OF Xanthium IN RELATION 



TO NUMBER OF INDUCTION PERIODS 



VICTOR A. GREULACH and JOHN G. HAESLOOP 

 Department of Botany, University of North Carolina, Chapel Hill 



Lang (1956) reported that biennial Hyoscyamus niger treated with 

 gibberellin bolted and bloomed the first season without cold or long- 

 day treatment, and that the annual form (a long-day plant) bloomed 

 under short days when treated with this growth substance. Soon after 

 his initial papers appeared Lang (1957) and other investigators, in- 

 cluding Lona (1956), Marth et al. (1956), and Wittwer and Bukovac 

 (1957), reported on the initiation or promotion of reproductive de- 

 velopment by gibberellin in various other species of plants. Some 38 

 species have been investigated, 17 of them long-day annuals, 9 bien- 

 nials, 9 day-neutral annuals, and 3 short-day annuals. Gibberellin 

 proved to be a substitute for long-day and cold treatments for all 

 species in the first two groups, except for the long-day plants rye and 

 Perilla. While induction of reproductive development was not a similar 

 problem in the day-neutral species, flowering was hastened by gib- 

 berellin in all species studied except pepper and geranium. No success 

 has been reported, however, with the few short-day species which have 

 been studied. Lang (1957) found that Biloxi soybeans and Xanthium 

 treated with gibberellin and kept under long days remained strictly 

 vegetative, and although Marth et al. (1956), observed earher bloom- 

 ing in gibberellin-treated Salvia, these plants were apparently under 

 inductive photoperiods. 



Lang (1957) came to the following conclusion: "It thus appears 

 that application of gibberellin allows numerous plants to overcome 

 cold and long-day requirements in flower formation but that it does not 

 substitute for any short-day requirement." 



The present study, initiated before the publication of Lang's results 

 with the two short-day species, was designed to obtain information on 



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