PLANT HORMONES 



211 



Figure 76. Plants showing two different responses to "plant hormones." A, Kal- 

 anchoe plants. Left: control plant; right: treated around the stem near the tip with 

 1.0 per cent /3-indolebutyric acid to induce adventitious roots. B, Tomato shoots. Left: 

 control plant; right: growth showing modification after the tip had been sprayed with 

 a solution containing a methyl substituted phenoxy acid. Many variations of this can 

 be induced with different substances having a formative influence. 



growth substances. Considerable attention has been given to compara- 

 tive activity ^^' ^^ and effects obtained with mixtures of root-inducing 

 substances.-" 



Propagation of plants. Substances detected by means described in the 

 preceding paragraphs may or may not have value for practical propagation. 

 For example, iS-indoleacetic acid is a very effective substance for inducing 

 epinasty when applied to tomato plants. It is not, however, as effective 

 for inducing roots as /3-indolebutyric acid, a-naphthaleneacetic acid, or 

 many of the substituted phenoxy acids. The best root-inducmg substances 

 are determined only by testing various substances and concentrations. By 

 this method it has been found that species of plants vary in their sensitivity 

 to the different substances. Generally speaking, /3-indolebutyric acid and 

 a-naphthaleneacetic acid together cover practically all the species require- 



