510 



M. /. Bukovac and S. H. Wittwer 



Flowering in lettuce (Lactuca sativa, 'Great Lakes' and 'Grand 

 Rapids'). Plants were grown in pot cultures in a greenhouse under 

 the prevailing winter photoperiod (9 to 1 1 hrs.) and at a night tempera- 

 ture of 18° C. After six to eight true leaves had developed, 3 X 10"^ M 

 solutions of the various gibberellins were applied to the stern apices, 

 and the treatment repeated after two and four weeks. 



Gibberellins Aj and Ag were considerably more active than Ag 

 and A4, both in accelerating flowering (Table 2) and stimulating seed- 

 stalk elongation (Figure 4). While no significant differences were noted 



2 3 4 



WEEKS AFTER 



5 6 7 



TREATMENT 



8 



Fig. 4. Rate of seedstalk elongation in 'Grand Rapids' leaf lettuce following appli- 

 cation of gibberellins Aj, Ao, A,, and kt to the youngest unfolding leaf. (Three 

 applications of 10 ^^1. of 3 x 10"^ ^ solutions at 2-week intervals.) 



