FORMATION AND OCCURRENCE OF AUXINS 71 



auxin present in carcinomas, or in animal tissues in general. 

 Fischer found no effect of auxins on the growth of animal 

 tissue cultures (see Kogl, Haagen Smit, and Tonnis, 1933) ; 

 this, however, is not conclusive proof of the ineffectiveness 

 of auxin, since the embryonic fluid which is used for tissue 

 cultures is relatively rich in auxin (u). The fact that the 

 large quantity of auxin in the urine is derived partly from 

 the food and partly from the action of bacteria in the in- 

 testine also does not support the view that auxin plays any 

 part in animal growth. 



Robinson and Woodside (1937) have followed the auxin 

 formation in the hen's egg during its development. The 

 auxin, which is principally in the embryo, increases parallel 

 to the increase in weight of the embryo for the first 7 days; 

 thereafter it increases rapidly to reach a maximum of 

 40,000 plant units, or about 1 7 of auxin, at about 14 days. 

 Finally it decreases again. Although the parallelism between 

 the auxin content and the growth is suggestive, there are no 

 direct experiments to show that the growth is in any way 

 due to the auxin. 



Navez and Kropp (1934) and Kropp and Crozier (1934) 

 found that extracts of crustacean eye-stalks contain an auxin. 

 In view of the facts above it is not surprising to find auxin in 

 lower as well as in higher animals, but here again there is 

 no reason to ascribe any physiological significance to it. 

 The attempt of Navez and Kropp to associate the auxin 

 with the chromatophore activator also present in the ex- 

 tracts seems quite unwarranted, since auxin itself had no 

 effect on the chromatophores. 



E. Production of Auxin by Microorganisms 



Nielsen (1930) was the first to show that an auxin, which 

 he named "Rhizopin," is produced in the growth of fungi. 

 Subsequently he (1931, 1932), Boysen Jensen (1931, 1931a, 

 1932), Kogl and Haagen Smit (1931), Dolk and Thimann 

 (1932), and Thimann and Dolk (1933) showed that nu- 

 merous fungi and bacteria are able to produce auxin in 



