Natural auxins 



of a substance which is the precursor of Z. This precursor is either active 

 itself or is converted to an active substance by the action of the coleoptile 

 tissues during bio-assay. 



Zone Z was eluted from Figure 5{a) and attempts were made to extract it 

 with ether. It remained almost entirely in the aqueous fraction, however, 

 and this result, together with the lack of reaction with the colour sprays, is 

 evidence against Z being IAN. 



Further experiments similar to the ones reported above were carried out 

 with seedling roots, and essentially the same results were obtained, with two 

 peaks of activity in ^jopropanol/ammonia and three peaks, X, Y , and Z, in 



i" 





>< 72 



lAA 



IAN 



^ 



¥- 



Response to lAA 



(mg/l.) 



0-2 



o-v- 



0-e 



OS 



10 



'f 



Figure 6. Aqueous fraction of germinating maize seeds developed in ammoniacal isopropanol. 



w-butanol/ammonia. This fact is important, in view of the large amount of 

 work now performed on excised tissues, and in particular on excised roots. 

 If the results of work on excised tissues are to be of any real value in plant 

 physiology, then we must have a comparison between excised and intact 

 tissues. 



Aqueous fraction of maize roots and seeds 



In these experiments there was again considerable activity in the aqueous 

 fractions, just as was found in both cabbage and tomato. The maize roots 

 showed a pattern of hormone activity similar in many respects to that 

 obtained with tomato roots, in both ammoniacal uopropanol and ammoniacal 

 ;?-butanol. Full details of these results will be presented elsewhere as they do 

 not contribute anything further to the present discussion. Chromatography 

 of the aqueous extract from maize seeds, however, is worth considering in 

 detail at this stage as it led to an investigation of 3-indolylpyruvic acid 

 (IPyA), a hormone reported to be present in maize seeds (Stowe and 

 Thimann, 1953). The results of chromatography of an aqueous extract are 

 shown in Figure 6. 



Again there is considerable activity in the lAA region and some near the 

 solvent front, but the region we wish to consider in particular is the zone of 

 activity approximately half-way between the starting line and the lAA zone. 

 This corresponds to the zone of activity found by Stowe and Thimann in 

 extracts of dormant maize seeds, and identified by them as IPyA. Slight 

 activity in a similar position was found in cabbage extracts in the aqueous 



48 



