INFLUENCE OF GIBBERELLIC ACID 361 



Table I. Effect of Gibberellic Acid on Fresh and Dry Weights of Burs of XaiUliium 



Mean Fresh Weight, g Mean Dry Weight, g 



usual findings, all gibberellin-treated plants had more nodes than the 

 control plants, though this may have been due to more prompt inter- 

 node elongation rather than to the formation of additional nodes. Al- 

 though stem diameter was not measured, it was obvious that the stems 

 of the treated plants were uniformly more slender than those of the 



" Inflorescence primordia present in all five plants. 



*■ Four plants with macroscopic flower buds, one with inflorescence primordia. 



controls (Fig. 1). All plants under long days were still strictly vegeta- 

 tive at the end of the experiment, while all plants given six or more 

 long nights had well-developed macroscopic flower buds. However, the 

 control plants given two and four induction periods had developed only 

 microscopic inflorescence primordia, stages 2 and 3 of Salisbury 

 (1955) — while all but one of the gibberellin-treated plants given these 

 photoperiodic treatments had macroscopic flower buds (Table II, Fig. 

 1 ) . Acceleration of reproductive development by gibberellin was also 

 evident in the plants given six to ten induction periods, particularly as 

 regards pistillate influences in the 10-day group. 



These results substantiate Lang's conclusion that gibberellin does 

 not substitute for any short-day requirement as far as flower initiation 



