Chemical structure and biological activity 



V^ 



® 



I 



■0-C-COOH 



H 



(Vluir and Hansch,1953) 



0-C-COOH 

 I 



+ 



aC-COOH 



(Veldstra,l953) 



V^ 



-C — COOH 

 I 

 H 



[;J=^^^^>p0-CH2C00H 



Thimann, 1951 

 Wahr//soOdane partition (Van Ovenbeek et al.,1355) 



c^^^^CHjCOOH 



270 



15 



aO-CHgCOOH 



(Thimann, i95l) CI 



f;==^0CH2C00H 



CI 



^ 



V^ 



CI 



— C — COOH 

 I 

 H 



CL 



^^ 



■0 — C — COOH 

 I 

 CI H 



(Osborne etal,l954) 



Figure 1. Comparison between pairs of regulators. The member on the right has the higher physio- 

 logical {auxin) activity. It is argued that this is so because the more active member penetrates the cell better. 



Figure 2. Reversible inhibition of indoleacetic acid (lAA) induced growth of maize coleoptile sections 

 by 2:4:-dichlorophenylmaleimide {MAL). {After van Overbeek et al., 1955.) 



206 



