42 



Fundamentals of Auxin Action 



erally using other species of plants. Among these could be mentioned 

 Ready and Grant (1947), Moewus (1949), Aberg (1950), Leaper and 

 Bishop (1950) and Audus (1951). An elegant technique has been used 

 by Burstrom (1950) in which the primary modification has been the 

 use of a constantly flowing test solution. For simplicity Swanson's 

 technique will be described here. 



The physiological basis of the root inhibition tests is the inhibi- 

 tion of growth of most roots by very low auxin concentrations. Most 

 roots have an extremely low auxin requirement for optimal growth 

 (Fiedler, 1936), and consequently most roots will respond to added 

 auxins by growth inhibition. 



PROCEDURE FOR THE ROOT INHIBITION TEST 



1. Sterilize seeds of Silver King corn in hypochlorite. 



2. Germinate on moist filter paper, embryo side down. 



3. After 48 hours select seedlings with roots 15 to 25 mm. long; measure, and 

 place in Petri dish containing 15 ml. of test solution. 



4. Measure growth after 48 hours. 



This test has been used successfully to assay for auxins in soil leach- 

 ings, and filtrates from various biological materials. It is sensitive to 



O.OOi 0.01 0.1 



CONG. OF AUXIN 



I M6/L 



Fig. 21. Results of a cress root inhibition test (Moewus et al, 1952). 



