Extraction and Measurement Techniques 59 



begun. Unfortunately there are a good many papers in the literature 

 which demonstrate apparent auxin activity for compounds which are 

 not auxins at all, the tests having been carried out in the presence of 

 some indigenous auxin. This type of error has led to some highly 

 erroneous conclusions. 



Lack of activity in the Avena test does not conclusively demon- 

 strate the absence of auxin activity. Substances, such as phenylacetic 

 acid, which are not effectively transported in the coleoptile and hence 

 fail to produce curvature may show auxin activity in the straight- 

 growth tests. 



In conclusion it should be reiterated that there is such a wide 

 variety of tests for auxins, some of them so extremely easy and others 

 so extremely sensitive, that one should not have to omit auxin assays 

 from any study where such data are needed. 



