498 B. O. Phinney 



The sums obtained from different extractions were then compared 

 with each other as a crude estimate of relative activities. 



Both methods of chromatography revealed two zones of gibberellin- 

 like activity from extracts of normal seedlings. Activity from silicic 

 acid chromatography appeared following elution with 20 per cent 

 ethyl acetate in chloroform, and again following elution with 60 per 

 cent ethyl acetate in chloroform; likewise two zones of activity were 

 found by paper chromatography, these being at Rf values of 0.15 and 

 0.43. Gibberellin-like activity was obtained from as little as 100 grams 

 of shoot tissue, fresh weight. Gibberellin A3 controls showed activity 

 from silicic acid chromatography in the fraction following elution 

 with 20 per cent ethyl acetate in chloroform, and at an Rf value of 

 0.41 from paper chromatography. 



No gibberellin-like activity was obtained from extracts of the mu- 

 tants d^, dr^, and an-^ either by paper chromatography or by silicic acid 

 chromatography. Additional extractions from 1 kg. samples failed to 

 reveal any evidence of activity. Extracts from the mutants rfi and ^2' 

 however, showed evidence of the presence of gibberellin-like sub- 

 stances from silicic acid chromatography and from paper chromato- 

 graphy. Two regions of activity were present which had positions in- 

 distinguisiiable from those obtained from normal seedlings. Compar- 

 isons of the total responses from the active fractions of c^^, d.^, and 

 normal material suggest that these mutants contain less than half as 

 much total gibberellin as do the normals. The responses were lower 

 whether compared on a fresh weight, dry weight, or per plant basis. 



Cross-Feeding Studies 



Only preliminary studies have been made to test for the accumu- 

 lation of unicjue gibberellin-like substances by the dwarf mutants of 

 Zea mays. Qualitative bioassays show the gibberellin-like substances 

 from the mutants <;/, and ^2 ^^d from normal seedlings to be rfi in- 

 active and d^, dr^, and arzi active. All fractions obtained from extracts 

 of the mutants d^, dr,, and an^ have been inactive when tested on the 

 five GAg-responding mutants. While the over-all activity obtained 

 from f/j and c?2 mutants is appreciably less than from normal plants, 

 regardless of the mutant used for bioassay, it should be emphasized 

 that more careful purification followed by the quantitative evalua- 

 tion of each active fraction is necessary for a proper evaluation of 

 the cross-feeding studies. The fractions obtained from extracts of 

 normal seedlings and from the dwarf mutants have not been tested 

 for activity on normal seedlings. 



DISCUSSION AND CONCLUSIONS 



Evidence is presented in this paper to support the interpretation 

 that the five mutant genes rf,, dc,, d^, d^, and a/?, arc responsible for 



