512 M. ]. Bukovac and S. H. Wittwer 



both varieties. Increasingly greater amounts, however, of A^ or A4 

 did not accelerate flowering, but the repeated dosages of 100 and 200 

 fji^. per plant resulted in seedstalks that were slightly taller than the 

 controls. 'Great Lakes' head lettuce plants treated with gibberellins 

 Ao or A4, up to total dosages of 400 fx%. per plant subsequently pro- 

 duced heads, as did the controls, and seedstalks later emerged through 

 the heads. By contrast, as little as 20 /xg. of A^ or A3 resulted in im- 

 mediate bolting, and head formation was bypassed. 



Parthenocarpic fruit groivtli of the tomato (Lycopersicon esculen- 

 tum, 'Michigan-Ohio Hybrid'). Tomato ovaries, were emasculated ap- 

 proximately 24 hrs. before anthesis, and treated with ten fx\. of a 3 X 

 10-5, 3 X 10'^> or 3 X 10"^ ^ solution of each gibberellin. As controls 

 for comparison, ovaries were also treated with indole-3-acetic acid 

 (lAA) and p-chlorophenoxyacetic acid (CIPA). Additional controls 

 consisted of emasculated and non-pollinated, as well as pollinated 

 ovaries. Three single plant replicates, each with 3 ovaries on the first 

 flower cluster comprised a treatment. The diameter of the ovaries 

 was measured after six clays. 



Ovaries treated with the 3 X 10-^ M concentration showed greater 

 growth with gibberellins A^, A3, or A4 than with lAA or CIPA, but 

 significantly less than the pollinated control. While gibberellin Ao 

 was not active at 3 X 10"^ ^l' it was as effective as any of the gibberel- 

 lins at 3 X 10"^ ^i- At the latter concentration all gibberellins pro- 

 duced ovaries of approximately the same size as the pollinated con- 

 trols and lAA, but smaller than those treated with CIPA (Table 2). 



Dormancy 



Dark-induced dormancy in seed of lettuce (Lactuca sativa, 'Grand 

 Rapids'). 2 ml. of a 100 p.p.m. solution of gibberellins A|, Ao, A3, A4, 

 or distilled water were added to 6-cm. petri dishes containing 50 seeds 

 on Whatman No. 1 filter paper. Seeds were germinated in the dark 

 at 26° C. for 96 hrs. All four gibberellins effectively replaced the light 

 requirement for germination (Table 2). 



Photo-induced dormancy of Weigela ('Vanicek'). Dormancy ^vas 

 induced in Weigela plants by exposure to a short (9 hr.) photoperiod. 

 Ten ^1. (3 X 10"^ ^I) of gibberellins A^, Ao, A3, or A4 were then ap- 

 plied to the dormant terminal buds at weekly intervals for four weeks. 

 Dormancy was partially broken by gibberellins A, and A;, but not 

 with A2 or A4 (Table 2). 



EVALUATION OF SEVERAL ESTERS OF GIBBERELLIN A3 



A homologous series of 7i-alkyl esters of gibberellin A3 (13) was 

 prepared with the appropriate alkyl iodide (10). Physiological activity 



