Natural auxins 



study measured auxin concentrations using the standard Avena method; 

 therefore it is difficuk to make direct comparison of lAA or I PA content 

 which might have influenced the curvature of the Avena sections. 



In summary, the evidence (Cooke, 1954; Vlitos and Meudt, 1954b) to 

 date does not support the hypotheses advanced for the role of auxin or of 

 indole derivatives in floral initiation. In the studies mentioned above where 

 a thorough attempt has been made to follow the levels of either indole 

 derivatives or unidentified auxins using two distinct techniques, the levels 

 of indole compounds in photoinduced plants appear to be related with 

 length of day rather than with floral induction. It is possible that the inhibi- 

 tion of flowering by exogenously applied auxins may be due to a general 

 inhibition of growth rather than any direct effect on floral tissue. In any 

 event, as newer experimental techniques become av^ailable workers in this 

 field will be in a better position to evaluate critically the many observational 

 and arbitrary hypotheses which have been advanced to account for photo- 

 periodism in plants, particularly those hypotheses which require a quantitative 

 interpretation. 



REFERENCES 



Block, R. J., LeStrange, R., and Zweig, G. (1952). Paper Chromatography , Academic 



Press, New York, p. 195. 

 Bonner, J., and Liverman, J. (1953). Hormonal control of flower initiation, Growth 



and differentiation in plants, Iowa State College Press, p. 283. 

 Cooke, A. R. (1954). Auxin content during the photoinduction of short-day plants. 



Plant Physiol. 29, 440. 

 Fisher, J. E., and Loomis, W. E. (1954). Auxin-florigen balance in flowering of 



soybean. Science, 119, 71. 

 GusTAFSON, F. G. (1941). The extraction of growth hormones from plants. Amer.J. 



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hormone in green plants. Plant Physiol. 21, 49. 

 Kefford, N. p. (1953). Properties of growth substances separated from plants by 



chromatography. Thesis, University of London. 

 Overbeek, J. VAN, Olivo, G. D., and Vazquez, E. S. de (1945). A rapid extraction 



method for free auxin and its application in geotropic reactions of bean seedlings 



and sugar cane nodes. Bot. Gaz. 106, 440. 

 Stowe, B. B., and Thimann, K. V. (1954). The paper chromatography of indole 



compounds and some indole containing auxins of plant tissues. Arch. Biochem. 



Biophys. 51, 499. 

 Terpstra, W. (1953). Extraction and identification of growth substances. Meded. 



bot. Lab. Rijksuniv., Gent, 4, 64. 

 Vlitos, A. J., and Meudt, W. (1953). The role of auxin in plant flowering. I. A 



quantitative method based on paper chromatography for the determination of 



indole compounds and of 3-indoleacetic acid in plant tissues. Contr. Boyce Thompson 



Inst. 17, 197. 

 Vlitos, A. J., and Meudt, W. (1954a). The role of auxin in plant flowering. 



II. Methods for the extraction and quantitative chemical determination of free 

 3-indoleacetic acid and other indole compounds from plant tissues. Contr. Boyce 

 Thompson Inst. 17, 401. 



Vlitos, A. J., and Meudt, W. (1954b). The role of auxin in plant flowering. 



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 photoinductive daylengths. Contr. Boyce Thompson Inst. 17, 413. 



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