264 Teubner, Wittwer, and Shen 



the corresponding mono-o)-^/?o or mono-meta compound. These rela- 

 tionships can also be applied to the trisubstituted iV-phenylphthalamic 

 acids which, in general, exhibit somewhat lower activity than the most 

 active of the related disubstituted forms. It is of particular interest 

 that di-or<//o-substituted forms (iV-2,6-dichlorophenyl-, A^-2,6-dimethyl- 

 phenyl-, A^-2,4,6-trichlorophenylphthalamic acids) are entirely devoid 

 of activity. 



Activity in Tomato Parthenocarpy 



While stimulation of tomato ovary development is not considered 

 a specific test for auxin activity (10), it has proved a convenient tool 

 for assessing the relative activities of a number of synthetic auxins 

 (12, 18). After preliminary tests to establish the appropriate effective 

 concentration range, the various substituted chloro- and methyl-de- 

 rivatives of AT-phenylphthalamic acid were evaluated relative to their 

 ability to stimulate development of tomato ovaries. The results pre- 

 sented in Table 2 indicate that activity of the various substituted N- 

 phenylphthalamic acids in stimulating parthenocarpy is almost iden- 

 tical to that obtained for tomato flower formation. Ovaries treated 

 with jt>ara-chlorophenoxyacetic acid, a typical auxin, had diameters 

 of 5.4 and 8.3 mm. at 10-^ and IQ-^M, respectively. This activity com- 

 pared favorably with that of N-S-chlorophenylphthalamic acid, but 

 was far less than that of the 2,3-dichloro- and 2,3,5-trichlorophenyl- 

 phthalamic acids. Indole-3-acetic and 2-naphthoxyacetic acids were 

 only one-tenth as active as para-chlorophenoxyacetic acid, and showed 

 an appreciable growth rate only at the highest concentration (lO'^AI) 

 tested. 



In tomato ovary growth as with flower formation di-or///o substi- 

 tution abolished activity. The low activity of the mono-para deriva- 

 tives in flower formation was also reflected in their failure to promote 

 parthenocarpic fruit development. In the latter case, there was a 

 stimulation of abscission of the young ovaries after 2 days which may 

 have masked any growth promoting effects. Non-treated ovaries did 

 not abscise during the test period of 5 days. The abscission caused by 

 mono-para substitution did not occur with the di-ortho derivatives, 

 although the 3,4-disubstituted chloro- and methyl-compounds showed 

 similar but less pronounced effects than tiie n\ono-para derivatives. 



Activity in Avena Section Straight Growth 



The high activity of some of the substituted A'^-phenylphthalamic 

 acids in stimulating fruit development prompted an evaluation of 

 their activities in the Avena section test. Earlier studies conducted 

 primarily with N-phenylphthalamic acid had given variable results 



