PLANT HORMONES 213 



ments. In some cases substituted phenoxy acids show considerably more 

 activity for inducing roots than these two, but they have not been thor- 

 oughly tested for practical purposes. 



Three methods of treating stem cuttings are to immerse the basal end of 

 the cutting in the given concentration of the chemical in water solutions; 

 to dip the basal end of the cutting into a powder preparation containing a 



Figure 78. Propagation with aid of root-inducing chemicals. A, Evonymous cuttings 

 showing increased rooting with increasing concentrations of /3-indolebutyric acid. Left 

 to right: non-treat-ed control, next three treated at base with solution of /3-indolebutyric 

 acid — 0.5 mg/hter, 1.0 mg/liter, and 2 mg/lit«r, respectively. The basal end of cuttings 

 were immersed in the solution for 24 hours, then planted in rooting medium. Photograph 

 taken after 20 days. B, Ilex cuttings showing the effects of the growth substance alcohohc 

 dip method. Left to right: control dipped in 50 per cent alcohol; basal end dipped in 5 mg 

 per cc of 50 per cent alcohol; 10 mg; and 20 mg, respectively. Cuttings were in rooting 

 medium 33 days before being photographed. 



given amount of the chemical; or to dip the basal end of the cutting into 

 an alcoholic solution of the substance or a concentrated water solution of 

 the substance. In a 24-hour immersion treatment, jS-indolebutyric acid is 

 used at a concentration of 0.5 to 80 mg of the acid per liter of water, the 

 optimum varying ^A-ith the species (Fig. 78A). or-Naphthaleneacetic acid is 

 effective over a range of 0.5 to 60 mg of the acid per liter of water. Halogen- 

 substituted phenoxy compounds must be used in low concentrations. For 

 example, a-(2,4-dichlorophenoxy)-propionic acid is effective over a range of 

 concentrations from less than 0.1 to 10 mg/1, the exact requirement varying 

 with the species. 



A second method, which has been found particularly effective, is kno^n 

 as the solution dip method. One to 10 mg of iS-indolebutyric acid in 50 per 

 cent alcohol makes an effective range of concentrations which can be used 



