46 



Fundamentals of Auxin Action 



fore, this test is not specific for auxins but may be very useful in com- 

 paring potential fruit-setting agents. It has been used as a growth 

 hormone assay (Luckwill, 1948). 



'0>ig 



AMOUNT OF AUXIN PER OVA»^ 



Fig. 23. Results of a tomato ovary test showing a quantitative increase in ovary 

 size as a function of concentration of beta-naphthoxyacetic acid (Luckwill, 1948). 



Other Tests 



A simple method for measuring auxins by means of lanolin paste 

 preparations smeared onto one side of a seedling was first described 

 by Laibach (1934). A simple version of the test has been used by 

 Wittwei (1943). An auxin preparation or plant extract is prepared 

 in pure lanolin, and a small dab applied to one side of the hypocotyls 

 of young bean seedlings. Three hours after the paste has been ap- 

 plied the negative curvature of the stem is read with a simple pro- 

 tractor. The test is sensitive to a range of concentrations from 0.1 to 

 1000 mg./liter of indoleacetic acid. This test is extremely convenient 

 and sufficiently accurate for many studies. 



Another method of measuring the growth-promoting properties 

 of auxins has been established using the hypocotyls of decapitated bean 

 seedlings (Weintraub et al, 1951). To each hypocotyl is applied about 

 0.001 ml. of an auxin solution in alcohol. The curvature obtained is 

 proportional to the logarithm of the concentration of 2,4-D between 

 the limits of about 10 to 60 mg./liter. 



