178 CHEMICAL AGENTS AND GROWTH 



responses other than leaf expansion and flowering are insufficient to 

 pinpoint their site of action with regard to the scheme presented in 

 Fia. 2. 



In conclusion, I would emphasize that some of the data presented 

 above are of a preliminary nature, and the interpretations are there- 

 fore rather tenuous. The concept of a series of reactions between the 

 initial light reaction and the final response is not new, but we have 

 never made extensive use of it in trying to relate the similarities and 

 differences among the various responses. It is reasonably certain that 

 the same reactions are not involved in every step between the perceiv- 

 ing of the light and the final response. By recognizing this fact and by 

 making more extensive use of the concept discusssed above, we can 

 begin to understand better the biochemistry of the whole field of photo- 

 periodic regulation of growth phenomena. 



REFERENCES 



Bonner, D. M. 1940. Leaf growth factors. Dissertation, California Institute of 



Technology, Pasadena. 

 Bonner, D. M., and A. J. Haagen-Smit. 1939. Leaf growth factors. II. The 



activity of pure substances in leaf growth. Proc. Natl. Acad. Sci. U. S., 25, 



184-88. 

 Bonner, D. M., A. J. Haagen-Smit, and F. W. Went. 1939. Leaf growth 



hormones. I. A bio-assay and source for leaf growth factors. Botan. Gaz., 



101, 128-44. 

 Borthwick, H. A., S. B. Hendricks, M. W. Parker, E. H. Toole, and V. K. 



Toole. 1952. A reversible photoreaction controlling seed germination. Proc. 



Natl. Acad. Sci. U. S., 38, 662-66. 

 Carter, C. E., and L. H. Cohen. 1956. The preparation and properties of 



adenylosuccinase and adenylosuccinic acid. /. Biol. Chem., 222, 17-30. 

 de Ropp, R. S. 1945. Studies in the physiology of leaf growth. I. The effect of 



various accessory growth factors on the growth of the first leaf of isolated 



stem tips or rye. Ann. Botany, 9, 369-81. 

 . 1947. Studies in the physiology of leaf growth. IV. The growth and be- 

 havior in vitro of dicotyledonous leaves and leaf fragments. Ann. Botany, 11, 



439-47. 

 Downs, R. J. 1955. Photoreversibility of leaf and hypocotyl elongation of dark- 

 grown red kidney bean seedlings. Plant Physiol., 30, 468-72. 

 Galston, A. W., and S. M. Siegel. 1954. Antiperoxidative action of the cobaltous 



ion and its consequences for plant growth. Science, 120, 1070-71. 

 Goodwin, R. H. 1941. On the inhibition of the first internode of Avena by light. 



Am. J. Botany, 28, 325-32. 



