Indole-3-acetaldehyde in Plant Extracts 51 



tempt was made to determine the activity in this zone more accurately. 

 The auxin present here is undoubtedly IAN. Zone III, which includes 

 the locus of lAAld, contained no definite colored spot, but only a very 

 faint purple streaking. The auxin activity found here was much higher 

 than expected from the faint coloration, and it seems probable that 

 a nonindole compound is responsible for this activity. Such nonindole 

 auxins were also reported to be present in members of the Cruciferae 

 by Linser and Machek (26) and by Housley and Bentley (17). Since 

 this activity occurred in the zone containing the locus of lAAld, we 

 first thought that it was due to this compound, but soil treatment 

 proved definitely that this was not the case. The activity was reduced 

 to less than one-tenth by the soil treatment, whereas it would have 

 been increased several-fold had it been due to lAAld. These results, 

 however, do not exclude the occurrence of lAAld in cabbage since 

 the starting material on the chromatogram represented less than 1/20 

 of the amount of plant material used in the case of Pisum. Linser, 

 Kiermayer, and Youssef (25) studied the auxins in Brassica napus 

 and three varieties of Brassica oleracea. Extracts of seeds, leaves, stems, 

 and roots of these plants were chromatographed in propanol, water, 

 ammonia (80:15:5) on filter paper. In stems of one of these plants, 

 B. oleracea var. sahauda (Wirsingkohl), auxin activity coincided 

 with the locus, giving a yellow color reaction with ferric chloride and 

 perchloric acid at Rf 0.77. The authors report that the color reaction 

 and position of this locus agree with those of synthetic lAAld, un- 

 fortunately, however, without mentioning the origin of their sample 

 of synthetic lAAld. As regards our ether extracts of heads of cabbage, 

 it can be concluded that, if present at all, lAAld occurs. 



The occurrence of IAN in members of the Cruciferae has been 

 established beyond doubt by isolation and chemical characterization. 

 As regards extracts of other plants, the identification of IAN rests ex- 

 clusively on chromatographic data. A survey of the literature on 

 chromatographic separation of auxins shows that IAN and a number 

 of other neutral auxins, now also including lAAld, run rather close 

 together in the majority of systems containing an aliphatic alcohol, 

 water, and ammonia. [The statement by Blommaert (5) that lAAld 

 runs at Rf 0.40 to 0.42 in n-butanol saturated with 2 A^ ammonia is 

 probably erroneous since IAN ran at Rf 0.87 to 1.0 in Blommaert's 

 system. Blommaert does not mention the source of his sample of 

 lAAld. ] Biological activity in the "IAN zone" of such systems does 

 not unequivocally indicate the presence of IAN. The activity may as 

 well have been due to other neutral auxins unless more specific tests 

 for IAN have also been carried out. 



