44 P. Larsen and T. Aasheim 



might sometimes have been confused with the nitrile (1, 2) . In certain 

 cases, however, the nitrile can be excluded as the active material in 

 the neutral preparations, namely when the auxin activity is de- 

 termined in the Avena coleoptile curvature test and found to be in- 

 creased several-fold by conversion of the active material to an acid. 

 The nitrile is already as active as indole-3-acetic acid (lAA) or even 

 more so (3, 24, and our own data) ; preparations containing it cannot 

 be made more active by any change in the nitrile molecule. Only a 

 concomitant removal of a growth inhibitor coidd explain the increase 

 in activity if the nitrile were the active, neutral material in such cases. 



In the early work by the senior writer (20, 21), only extracts of 

 etiolated pea epicotyls were thoroughly investigated, and the evidence 

 for the occurrence of lAAld actually pertained only to Pisum. \\^hen 

 the presence of a neutral growth substance in extracts of cabbage could 

 be demonstrated (21) , it was only by analogy that the identity of this 

 with lAAld was inferred. No attempts were actually made to establish 

 the aldehyde nature of this material. In light of the work of Bentley 

 and her co-workers, it would now be highly desirable to reinvestigate 

 the status of lAAld as an auxin. For several years we were discouraged 

 from resuming the work on lAAld, however, primarily on account of 

 the reported extreme lability of the compound, not to mention the 

 fact that in spite of its synthesis in 1952 it remained inaccessible for 

 research purposes. Recently, a number of findings have been reported 

 which should be favorable for a successful attempt to demonstrate the 

 presence of lAAld in plant extracts. 



First, a simplified method for obtaining chemically pure lAAld 

 was published by Gray in 1958-59 (13, 14) utilizing Langheld's 

 method in treating tryptophan with sodium hypochlorite, but intro- 

 ducing the refinement of trapping the aldehyde in benzene before it 

 would become destroyed in the reaction mixture. According to Gray, 

 the aldehyde is not nearly as labile as had been believed; and its 

 sodium hydrosulfite addition product proved to be stable for many 

 years. 



In the meantime, Nitsch and Nitsch, 1955 (28), and Nitsch, 1956 

 (27) , had been searching for a chromatographic solvent system that 

 would separate various neutral auxins on filter paper. As a result of 

 tlieir extensive investigations they recommended 7?-hcxane or a prac- 

 tical grade hexane to be used in a water-saturated atmosphere. Such 

 a system, which contains no acid or alkaline component and very little 

 water, should be considerably less harmful to an inistablc compound 

 like lAAld than most of the systems j)reviously preferred in chroma- 

 tograj)hic work on auxins. \i\ addition, the hexane gives a much better 

 separation of known neutral auxins. 



