44 



Fundamentals of Auxin Action 



\'alentine beans are recommended as the most sensitive variety and red kidney 

 beans as a somewhat less sensitive alternative. 



Application 



Solutions to be tested are made up in 95% ethyl alcohol containing 1% Tween 

 20 or other detergent. Pipette 0.005 ml. of each solution on each of 10 to 20 

 expanding trifoliate leaves. 



Reading 



After 5 to 13 days remove the expanded trifoliate leaves and compare on 

 either a weight or leaf area basis. 



This leaf repression method is an effective test for sohitions of 

 2,4-D ranging from 1 to 100 mg./liter. Each plant receives from 0.005 

 to 0.5 micrograms of auxin. Comparisons of leaf area give results with 

 slightly greater sensitivity than comparisons of weight differences; 



1007c 



80 



60 



40 



o 



X 



z 



LEAF 

 AREA 



/ 



0.0025 0.005 0.01 0.025 0.05 0.1 



AMOUNT OF 2,40 PER PLANT 



025 0.5 UG 



Fig. 22. Results of a leaf repression test showing the semi-logarithmic inhibition 

 of leaf area and leaf weight at varying conceatrations of auxin, 2,4-dichlorophe- 

 noxyacetic acid (Brown and Weintraub, 1950). 



