EFFECTS OF GIBBERELLIN 377 



Table II. Modifying Effects of Gibberellin on the Photoperiodic Responses of 

 Cosmos (C. bipinnatus, variety Sensation), a Facultative Short-Day Plant 



''Flowering in signiiicantly fewer days than controls (P = 0.01). 



trast, Cosmos that flowered under long days without gibberellin 

 formed flower buds significantly later, and 25% remained vegetative 

 (Fig. 1). 



Cosmos bipinnatus Cav.- obviously does not have an obligatory 

 short-day requirement for flowering, since most plants will eventually 



Table III. Flowering of Cosmos (C. bipinnatus, variety Sensation) at an 18-hr 

 Photoperiod Following Foliar Sprays of Gibberellin at \'arious Stages of Growth 



Gibberellin Concentration, ppm 



" Days to visible flower buds. 



" Flowering in significantly fewer days than controls (P = 0.05). 



flower in long days. Accordingly a large number of plants maintained 

 under long days were treated with several concentrations of gibberellin 

 at various stages of growth as determined by node numbers (Table 

 III). Plants which initiated flower buds under long days were elimi- 

 nated at successively later growth stages. Only those which remained 



-Variety Sensation, Ferry Morse Seed Co., Detroit, Michigan. 



