Rooting 207 



METHODS OF TREATMENT 



Selection of Auxins 



A very wide variety of auxins has been used for the rooting ol 

 cuttings, but the one most commonly used with great success is in 

 dolebutyric acid. It appears probable that the success of this compound 

 may be because its auxin activity is weak and it is slowly destroyed 

 by the auxin-destroying enzyme system described in chapter III. 

 Naphthaleneacetic acid and indoleacetic acid have also been used but 

 with less uniform success. The former is quite a strong auxin and 

 the latter is very readily destroyed. Because the phenoxyacetic acids are 

 strong auxins they are highly effective in inducing the formation of 

 root primordia. However, they are also very likely to inhibit bud and 

 root growth (Hitchcock and Zimmerman, 1942) as well as cause leaf 

 injuries. The phenoxy a-propionic and a-butyric derivatives, how- 

 ever, seem to be more promising as rooting auxins since they show 

 less inhibitory characteristics. Several of these auxins with branched 

 side-chains have been found to be superior even to indolebutyric acid. 



CHgCHgCHgCOOH 



J 



H 

 Indolebutyric Acid a-2,4,5-Trichlorophenoxypropionic Acid 



In selecting auxins for rooting, it seems that in general the strong 

 auxins are undesirable as they inhibit bud and root development. 

 Consequently weak auxins are generally selected. Another quality to 

 select for is solubility, particularly since treatment of cuttings by 

 dipping in auxin solutions requires high concentrations and conse- 

 quently high solubilities. Because the acids are generally less soluble 

 than the salts, the latter derivatives are more commonly used. The 

 amide derivative has been used occasionally (Stoutemyer, 1941). It 

 exhibits greater solubility and at the same time possibly more rapid 

 penetration into the tissues. Mixtures of auxins have been found in 

 some instances to be more effective than the one auxin alone (Hitch- 

 cock and Zimmerman, 1940). This interaction between auxins sug- 

 gests synergistic activity, A striking improvement of rooting response 

 to auxins in the presence of auxin synergists has been reported by van 

 Raalte (1951). 



Extensive compilations of reports concerning the relative effective- 

 ness of different auxins in rooting of various species have been pub- 



