Extraction and Measurement Techniques 45 



however, the simplicity of weight determinations would appear to 

 make this a generally more feasible method. 



A concentration curve obtained from a leaf repression test is 

 shown in figure 22. Both leaf area and weight responses are included 

 for comparison. 



The leaf repression test is valuable as an easy test for which no 

 environmental controls are necessary. Its limitations are a low sensi- 

 tivity and a lack of specificity for auxins. These limitations, however, 

 are negligible when it is used for herbicide studies. The technique is 

 so simple and convenient that it affords a valuable means of compar- 

 ing such substances as potential herbicidal materials. 



The Tomato Ovary Test 



A well-known property of auxins is the capacity to set partheno- 

 carpic fruit, particularly in the tomato. The utilization of this property 

 as an assay method has been worked out by Luckwill (1948). The 

 method has not been standardized for auxins other than /3-naphthoxya- 

 cetic acid (BNOA) but shows considerable promise as an assay tech- 

 nique. 



PROCEDURE FOR THE TOMATO OVARY TEST 



Plant material 



Tomato plants are grown to the stage where the fust two clusters each have 

 two nearly opened flowers. Flowers are emasculated 1 to 2 days before opening 

 and the corolla and style are removed. All other flowers are removed from the 

 flower cluster. The use of male-sterile strains of tomato relieves the necessity for 

 emasculation. 



Application 



Solutions to be tested are applied with a 1 ml. hypodermic syringe, using 

 0.0225 ml. per flower. 



Reeding 



Ovary diameters are measured after 6 days. 



The growth of the ovary is proportional to the logarithm of the 

 concentration of the growth regulator within the limits of 0.1 to 10 

 micrograms per flower. This range represents a concentration in the 

 stock solutions of 1 to 100 mg./liter of BNOA. A sample dilution curve 

 is shown in figure 23. 



It is well known that the capacity to set fruit is not limited to 

 auxins alone. For example, substances such as colchicine and fluorenea- 

 cetic acid which apparently show no auxin activity in growth tests are 

 effective fruit-setting agents (Avery and Johnson, 1947, p. 175). There- 



