In the previous paper (Part 3, 1944)⁽¹⁾ it was reported that 1, 4-dihydro-, 3, 4-dihydro- and 1, 2, 3, 4-tetrahydro-naphthoic acid have the activity of producing the adventitious roots and in the last paper (Part 5)⁽²⁾ it was found that two of these (1, 4-dihydro- and 1, 2, 3, 4-tetrahydro-naphthoic acid) have also the strong epinasty-activity for the tomato-plant.
It had been supposed that these substances had no activity for plant growth, because these did not satisfy one of the minimum structural requirements for the plant-hormones suggested by KOEPFLI et al.⁽³⁾ As the continuation of the last experiment, twenty carboxylic acid derivatives were synthesized and the activities were tested by the previously reported method(Part 4)⁽⁴⁾. All of these compouds have carboxyl group(s) attached directly to the carbon ring.
The results obtained are illustrated in Fig.1.
No active substance has been found among these twenty compounds.