A. J. HAAGEN-SMIT I5 



broken molecule since repeated fractional precipitation of the protein 

 with ammonium sulfate did not remove the auxins. 



In seeds free and bound auxins have also been shown to occur. In corn 

 oil some of the auxin can be readily extracted with water, and consists 

 mainly of auxins-a and -b. Hydrolysis of the oil gives additional quantities 

 of auxins which are probably present in the ester form. When the entire 

 seed of cereal grains is treated with dilute alkaU, amounts of auxins are 

 found which are several times greater than those available from seeds 

 after extraction with water. This liberated auxin was isolated and shown 

 to consist mainly of indoleacetic acid (2,19). 



As Gordon and Wildman (16) have shown, some of this liberated 

 auxin has its origin in tryptophan, which releases under mild treatment 

 small quantities of indoleacetic acid measurable in the Avena test. It is, 

 for example, unstable at 37°C. at pW 10.5, or in contact with cold 

 phosphate buffer at pW 4.6. Even melting with agar releases some growth 

 hormone. Similar degradations of tryptophan take place within the 

 plant, and it has been shown that an enzyme is responsible for this 

 conversion. 



These findings do not invalidate all conclusions based on previous 

 auxin extraction methods. However, they must be considered in future 

 work. When, for example, wheat or corn is treated at a pW of 10.5 for 

 two days, an increase of 5 milligrams per kilogram in the auxin content 

 is noted over the readily extractable auxin. As Avery and Berger (i) 

 have shown, it is safe to conclude that this amount represents auxin in 

 bound form and is not due to the conversion of proteins containing 

 tryptophan. Avery and Berger purified the auxin complex and found 

 it to be protein-like. Skoog (53) has shown in the Avena that inactive 

 precursors originating in the seed travel upwards and are able to induce 

 growth of the coleoptile after 2 to 6 hours. It is possible that the auxin 

 complexes mentioned serve as the auxin reserve for the plant. Since 

 Wildman et al. (71) discovered an enzyme which converts tryptophan 

 to indoleacetic acid we have to include this substance and tryptophan- 

 containing proteins as potential sources of auxins in the plant. 



The proportion of free to bound auxin varies greatly in different plants 

 and plant parts. In hemna only two per cent is free according to Thimann 

 (59), whereas the free auxins in Avena coleoptile tips account for nearly 

 all of the total auxin. The study of the relative proportions of free and 

 bound auxin is of importance for the understanding of several growth 



