222 



GROWTH OF PLANTS 



in addition to many other hormone-like effects. The following graphic 

 formulas illustrate the structure of one acid in each group: 



0— CH2— COOH 



-O— CH2COOH 



COOH 

 I 



I 



^-Naphthoxy acetic acid 4-Chlorophenoxyacetic add 2 ,4,5-Tniodobenzoic acid 



The degree of activity varied with the groups or elements substituted, 

 with the number and location of substitutions, and in higher homologs 

 with the place of attachment of the chain to the ring of the molecule. The 

 comparative influence of groups and elements and the location of the substi- 

 tution are illustrated in Table 24. The activity referred to in this case is 

 the power to induce cell elongation. When a formative influence is involved, 

 still other differences are evident. The illustration shows that the NO2 



