p. W. ZIMMERMAN 



179 



produce the spongy mesophyll. The veins are initiated by divisions of 

 rows of cells in the layer beneath the embryonic palisade. Many inter- 

 cellular spaces (air) normally appear in the spongy tissue. 



Using three substituted phenoxy acids Burton found that these were 

 more or less specific for given structural variations from normal. For 

 example, 2-chlorophenoxyacetic acid inhibited the formation of inter- 

 cellular spaces in the spongy tissue; 4-chlorophenoxyacetic acid inhibited 

 the activity of the plate meristem (between the veins) and the veins 

 became approximate with continuous parenchyma. 2,4-D brought about 



TABLE 3 



Molecular configuration and comparative activity of substituted phenoxyali- 



phatic acids involving the tomato plant as test object 



Xylenoxy compounds 



Cell Formative 



elongation effects 



3,5-Dimethylphenoxyacetic acid 

 a-(3,5-Dimethylphenoxy)propionic acid 

 Q:-(3,5-Dimethylphenoxy) butyric acid 

 2,5-Dimethylphenoxyacetic acid 

 a:-(2,5-Dimethylphenoxy)propionic acid 

 Q:-(2,5-Dimethylphenoxy)butyric acid 

 3,4-Dimethylphenoxyacetic acid 

 a!-(3,4-Dimethylphenoxy)propionic acid 

 Q:-(3,4-Dimethylphenoxy)butyric acid 

 2,4-Dimethylphenoxyacetic acid 

 a:-(2,4-Dimethylphenoxy)propionic acid 

 Q:-(2,4-Dimethylphenoxy) butyric acid 



a progressive modification of all leaves developed after the chemical was 

 applied. The latter compound also caused various structural modifica- 

 tions similar to those of both the other acids. Chlorenchymous tissue 

 was usually confined to the margin, and cells without chlorophyll over 

 vascular tissue gave the veins a transparent effect. Burton worked on 

 only one species, the bean. It will be interesting to see how structures of 

 other species respond to the same chemicals. 



Modification of flowering habit and correlation of organs induced with 

 substituted benzoic acids are illustrations of special chemical influence. 

 In 1942 Zimmerman and Hitchcock (14) reported that the pattern of 

 leaves, the flowering habit, and correlation of organs were modified by 

 means of 2,3,5-triiodobenzoic acid. They showed that flower clusters 



