Physical-Chonical Aspects uf Synthetic Auxins 303 



30. Veldstia, H. The relation of chemical structure to biological activity in growth 

 substances. Ann. Rev. Plant Physiol. 4: 151-198. 1953. 



31. Velick, S. F. Fluorescence spectra and polarization of glyceraldehyde-3-phos- 

 phate and lactic dehydrogenase coenzyme complexes. Jour. Biol. Chem. 233: 

 1455-1467. 1958. 



32. Westphal, U. Steroid-protein interactions. III. Spectrophotometric demon- 

 stration of interaction between proteins and progesterone deoxycorticosterone 

 and Cortisol. Arch. Biochem. Biophys. 66: 71-90. 1957. 



33. ^Voodford, E. K., Holly, K., and McCready, C. C. Herbicides. Ann. Rev. 

 Plant Physiol. 9: 311-358. 1958. 



34. Wort, D. J. Influence of 2,4-D on enzyme systems. Weeds. 3: 131-135. 1954. 



35. Wright, R. H. Physical basis of insect repellency. Nature. 178: 638. 1956. 



36. Zimmerman, P. W., and Hitchcock, A. E. The response of roots to "root- 

 forming" substances. Contr. Boyce Thompson Inst. 7: 439-445. 1935. 



37. , and Hitchcock, A. E. Formative effects induced with /3-naphthoxyacetic 



acid. Contr. Boyce Thompson Inst. 12: 1-14. 1941. 



33. , and Hitchcock, A. E. Substituted phenoxy and benzoic acid growth 



substances and the relation of structure to physiological activity. Contr. Boyce 

 Thompson Inst. 12: 321-343. 1942. 



DISCUSSION 



Dr. Wain: I would like to point out the clanger of assuming that 

 the reason phenoxyacetic acid is held to a protein and is unable to 

 pass through a membrane in dialysis, is due to the fact that the ring 

 system has been associated with the protein. There may be an asso- 

 ciation of poles of opposite charge. There could be, for instance, a 

 protein with a free NHo group that could very readily associate with 

 the carboxyl group of the phenoxyacetic acid to give an association 

 of the molecule with the protein which has nothing to do with the 

 ring system. Nevertheless, I fully agree that the ring system is all im- 

 portant, and what is more, the ring system must be an unsaturated 

 ring system. The unsaturated benzene ring is flat, and it is well known 

 that flat surfaces can readily attach themselves to other surfaces by 

 Van der Waal's forces. Benzene itself is capable of forming molecular 

 compotmds with mercuric cyanide and platinum chloride, for ex- 

 ample, and presumably is providing one coordinate valency. It may 

 well be, therefore, that there is something of this kind taking place 

 with the benzene ring to give: a free pair of electrons. I'm not sug- 

 gesting that that known pair is donated to form a rigid coordinate 

 bond, but the electron density outer surface may very well be slightly 

 modified by this kind of tendency so as to give an association with 

 the benzene ring, which after all is perhaps significant in view of the 

 fact that there must be unsaturation in the ring. Many people work- 

 ing in this field of auxinology are closing their eyes and are ignoring 

 the fact that ethylene, carbon monoxide, propylene, etc., are active 

 as plant growth regulators. 



Dr. van Overbeek: I agree with Dr. Freed on the emphasis he has 



