E -50--60 --70--80-I I 1 1 h (w). 200 2 50 300 350 Figure 7. in EPA at +25 and -192".Circular dichroism curves of 5a-pregnan-20-one (XI) can be expected for XII. The relevant C.D. curves are shown in Figure 7 and, on the basis of the strong negative rotational strength, conformer XI does indeed seem to be the preferred one. The rotational strength of XI ( R O Z 5 = -6.9 X c.g.s., Ro-lg2 = -7.4 X c.g.s.) is only slightly affected by lowering the temperature. Since the rotational strengths of the two preferred conformations are predicted by the octant rule4 to be appreciably different, this result implies a large free energy for the interconversion of XI and XI1 probably approaching 2 kcal. (see Figure 3), if entropy differences in the two conformers are small. ExperimentalAll measurements were performed in Spectrogride solvents. The EPA solvent consisted of ether-isopentane-ethanol in a ratio of 5 : 5 : 2 by volume; C.D. curves were obtained, using a Baird-Atomic Jouan dichrograph operating with a photomultiplier voltage of 1.2 kv. and following the procedures and molecular ellipticity calculations outlined earlier. 39 We wish to thank Drs. P. Crabbe and A. D. Cross (Syntex, S . A., Mexico City) and Dr. G. Snatzke (University of Bonn) for furnishing pertinent manuscripts. Also, Dr. J. S. Mills (National Gallery, London) provided a sample of 3P-acetoxyhexanordammar-20-0ne,~O and Dr. CrabbC supplied samples of 30-acetoxy-l6P-cyano-A5-pregnen-20-one4l and 3P-acetoxy-16P-methyl-A5-pregnen-20-one. The technical assistance of Ruth Records and W. s. Briggs is gratefully acknowledged.Acknowledgment.

Abstract. The application of gibberellic acid (GA3) to the non-rosette long-day plant Lemna gibba G3 at concentrations from 0.1 to 100 mg/l did not induce flowering on short days and inhibited flowering on long days at ooncentrations of 1 mg/l and higher. On both short and long days GA3 concentrations above 1 mg/l caused a decrease in frond size and fresh and dry weight, but an increase in the rate of frond production and thus an increase in the # VF (number of vegetative fronds). Identical results were obtained when gibberellin A7 was used instead of GA3.The addition of the plant growth retardant CCC [ (2-chloroethyl) trimethylammonium chloride] to the culture medium on long days resulted in almost complete inhibition of flowering at 10-3 M. Vegetative growth was also inhibited to some extent. With CCC at 10-3 M the simultaneous addition of GA3 resulted in partial reversal of flower inhibition with 0.3 mg/l GA3 being optimal. The inhibition of vegetative growth as measured by fresh and dry weight was also partially reversed by GA3, but the threshold concentration for reversal of flower inhibition was at least 10 times lower than that for inhibition of vegetative growth.These results are interpreted as indicating that gibberellins are important for flowering in the non-rosette long-day plant L. gibba G3, but apparently are present in non-limiting concentrations on short days.Gibberellic acid (GA3) is known to cause stem elongation and flower induction in many rosette long-day plants (11,12). Induction of flowering by GA3 has also been reported in the non-rosette longday plant Loliumn temnulentuni (6), the long-short-day plant Bryophyllum daigremitonitianunt (22), and the short-day plant Impatiens balsamnina (14). However, in of the plant growth retardants CCC [(2-chloroethyl) trimethv lammonium chloride] and AMO 1618 (2-isopropyl-4 -dimethylamino-5-methvlphenyl-l -piperidinecarboxvlate methyl chloride) which are thought to act primarily bv inhibiting endogenous gibberellin biosynthesis (5,7,10,15,18). The application of CCC or AMO 1618 to the long-day rosette plant, Sacitolts parvifloruts, the long-short-day plant, Bryophyllunm daigremontianum, and also the short-day plant, Pharbitis .il, when grown on inductive photoperiods, resulted in complete or nearly complete inhibition of flowering with only a small accompanying inhibition, of growth (1, 23.24). In each case the simultaneous application of GA3 reversed the inhibition of both flowering ancd growth, but a 10 to 50-fold higher concentration of GA3 was required to reverse the inhibition of growth than was needed to reverse the inhibition of flowering.These results provided further evidence that gibberellins might be important for flower induction in long-day rosette plants and in the long-short-day plant Bryophyllumn. In addition, the results with Pharbitis suggested that even in plants for which GA3 treatment does not result in flower induction, gibberellins might be involved in the flowering process. In view of these results it was felt that similar exper...

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