Chemistry and Qrowth 



suggestion that skatole may act in the plant as a growth- 

 promoting hormone fails to convince, for lack of evidence that 

 skatole is elaborated by the plant. 



The report by Snow (1937) that benzoyl oxide and peroxide, 

 applied in lanolin, produced perceptible bending in dark- 

 grown oat coleoptiles, further complicates the issue. The 

 activity of these substances was, however, only about one 

 four-hundredth of that of indole-acetic acid. 



^/-indolyl-lactic acid was the only one of several indole 

 compounds prepared by Bauguess and Berg (1934) that was 

 inactive as a growth-substance (Bauguess, 1935). With one 

 exception it appears to be the only substance capable of 

 optical activity or resolution (other than /-tyrosine and /-try- 

 ptophan) of which the growth-regulating activity has been 

 tested, hence nothing can be said at present about the relative 

 growth-regulating power of most optical isomers. 



The exceptional case which has been investigated is that of 

 a- (Pi indolyl) -propionic acid, synthetized by Kogl (1938) 

 by a method not stated. This substance is optically active (its 

 racemic form is probably the same as Ellinger's indole- 

 methyl-aceticacid,p. 102 and 104). Kogl found that the Avena 

 activities of the racemic (+), and ( — ) acids were, in lo* 

 A.U. per gram, respectively 23, 48, and 1-6. Thus the (+) 

 acid is about 30 times as active in the Avena test as the 

 opposite enantiomorph is. See page 23 for reference. 



Compounds related to tyrosine as well as those related to 

 tryptophan have physiological activity. Extracts of thyroid 

 gland (containing thyroxin, an iodo-derivative of tyrosine) 

 were among the first of the animal hormones shown to affect 

 growth in plants (Nicol, 1937). Hammett (1936) writing 

 from a zoological standpoint, has suggested that attention 

 given to the iodine in thyroxin has overshadowed the import- 

 ance of its tyrosine residue. 



As a matter of interest, and without comment (except to 

 point out that creatinine and creatine have not been shown to 

 be growth substances in the modern sense of an accessory 

 rather than a nutrient), the formulae of auxin-a, indole-3- 

 acetic acid, creatinine, and creatine may be given side by side : 



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