Plant Qrowth'Suhstances 



is the product. Apparently, urorosein and the indole-acetic 

 acid nitritation compound behave differently with alkalis. 

 On account of the apparent absence of information regarding 

 the behaviour of urorosein in ethyl acetate, the question of 

 the identity of the two substances in question must be left 

 open. Plimmer (1918) wrote that urorosein is most probably 

 nitroso-indole-acetic acid. Ellinger and Flamand (1909) and 

 Riesser (191 1) believed urorosein to belong to the group of 

 tri-indolylmethane dyes discovered by Ellinger and Flamand ; 

 Weise {loc. cit., p. 768) imputed to H. Fischer (1923) the 

 view that it is a di-indolyl-methene derivative. Urorosein has 

 also been studied by Herter (1908). 



Schmitz (193 1 ), apparently quoting Riesser (191 1), wrote: 

 "Eine Darstellung des Uroroseins in Substanz ist bisher 

 nur auf synthetischem Wege durch Oxydation von Indole- 

 essigsaure mit Eisenchlorid oder mit Natriumnitrit und 

 Salzsaure versucht worden." 



Further pursuit of the subject is left to those particularly 

 interested. 



With the modified Adamkiewicz-Hopkins (tryptophan) 

 reaction of Winkler (1934), indole-acetic acid gives a reddish 

 violet colour. The best ratio of reagents is i mol. of indole- 

 acetic acid, I mol. of glyoxylic acid, 2 mol. Cu (sulphate or 

 acetate) and excess of concentrated sulphuric acid — added in 

 that order. (Winkler and Petersen, 1935). 



For titration-curves of 3 -indole-acetic, -propionic and 

 -butyric acids in distilled water, see the paper by Albaum 

 and Kaiser (1937). 



A study of three colorimetric methods of estimating indole- 

 acetic acid in aqueous solution has been made by Mitchell 

 and Brunstetter (1939). 



See also Lefevre (1939, G). 



Methods of Isolation of indole-acetic acid 



The Avena (oat) test has been used by Kogl et al. (1934) 

 as a method of assay of indole-acetic acid in fractions of urine 

 during the process of isolation. The normal urinary excretion 



126 



