262 Teubner, Wittwer, and Shen 



at the ortho or meta positions enhanced flower forming activity while 

 hydroxyl- or nitro- groups at either the ortho, meta, or para positions 

 in the phenyl ring rendered the weakly active N-phenylphthalamic 

 acid inactive. Substitution of chloro- or methyl- at the para position 

 did not abolish the flower-forming activity of iV-phenylphthalamic 

 acid, although these derivatives had a high degree of phytotoxicity 

 which often masked their weak flower-forming activity. On the other 

 hand, substitution of bromo-, carboxyl-, amino-, dimethylamino-, or 

 acetyl- gioups at the para position resulted in derivatives which were 

 inactive at concentrations up to 500 p. p.m. The iV-2,5-dimcthoxy- 

 and iV-2-methyl-5-isopropylphenyIphthalamic acids were also mactive 

 in the preliminary tests. 



Replacement of the phenyl ring with a 1-naphthyl group (xV-1- 

 naphthylphthalamic acid) resulted in high phytotoxicity and forma- 

 tive effects, but no increase in flower numbers. On the other hand, N- 

 2-naphthylphthalamic acid exhibited no phytotoxic or formative ef- 

 fects and did give a slight increase in flower numbers.^ 



On the basis of these preliminary tests, all of the monochloro- and 

 dichloro- together with four of the six possible trichloro- derivatives 

 were evaluated in the tomato flowering test over their most effective 

 concentration ranges. In the same test A^-phenylphthalamic acid was 

 included together with its monomethyl- and several dimethyl- deriva- 

 tives. The results obtained are presented in Table 1 together with 

 their statistical significance. It is apparent that mono-ortho and mono- 

 meta substitutions on the phenyl ring are far more effective in en- 

 hancing the tomato flower forming activity of N-phenylphthalamic 

 acid than is para substitution. Furthermore, monomethyl substitution 

 is as effective, or nearly so, as monochloro substitution. The positional 

 effects of the mono-substituted derivatives are even more apparent if 

 the relative activities of the disubstituted derivatives are examined. 

 Thus, A''-2,3-dichlorophenylphthalamic acid reflects the activating ef- 

 fect of both ortho and meta substitution and is the most active deriva- 

 tive examined to date. 



In contrast to the effect of monomethyl substitution, the 2,3-di- 

 methyl derivative has surprisingly low activity. Similarly, 2,5-disubsti- 

 tution results in a slight depression of activity relative to the mono- 

 substituted derivatives. The relatively low activity of the parach\oro 

 and para-methyl derivatives is enhanced considerably by ortho substi- 

 tution and less so by a meta substituent. In these cases, however, the 

 relative activity of the disubstituted derivative is somewhat less than 



"Only a single lest of tlie napluliyl derivatives has been conducicd so thai 

 these results should be considered as tentative. 



