112 PHYTOHORMONES 

 C— CH2.CO.COOH 



10, 



.CH -^^^^ 



N'' + NH3 



H 



C— CHo.COOH 



II 

 .CH + CO2 



H 



The study of Frieber (1922) on the color reactions for indole 

 derivatives given by cultures of various bacteria makes it 

 probable that numerous bacteria, growing on peptone 

 media, produce indole-acetic acid.. The identification of the 

 auxins of yeast and Rhizopus with indole-acetic acid gives us 

 good reason to believe that the auxin found in cultures of 

 bacteria (Boysen Jensen, 1931) and certain other fungi 

 (Nielsen, 1931) is also indole-acetic acid. This agrees also 

 with the molecular weight determinations below. Boysen 

 Jensen (1932) however, has shown that Aspergillus niger 

 produces an auxin from histidine, lysine, leucine, tyrosine, 

 phenylalanine, and tryptophane, but not from glycine, 

 alanine, or arginine. These facts are difficult to interpret 

 unless chemically different substances, active on A vena, 

 are derived from these different amino-acids. However, it is 

 well-known that the synthetic acti\dties of fungi are very 

 great. 



So far as is known, the indole-acetic acid produced by 

 fungi has no effect on their growth. Nielsen (1931a) showed 

 that if the auxin-containing ether extract of medium on 

 which Rhizopus had grown were added to fresh medium, it 

 did not stimulate the growth of Aspergillus niger. The 

 auxin does, indeed, disappear from the medium in which it 

 is produced after some time, but there is no reason to suppose 

 its destruction is correlated with the growth of the fungus 

 (Thimann and Dolk, 1933). There is, however, a substance 

 or group of substances, produced by Rhizopus, which does 



