Rooting 203 



the control of differentiation is the physiological basis for the rooting 

 of cuttings as we understand it today. 



While it is not clear what the exact action of auxin in this process 

 is, there are several established facts concerning the auxin function. 

 The stiniidation of root formation is not restricted to auxins alone, 

 as similar responses can be obtained with compounds which increase 

 auxin activity and with (ompounds which are epinastic agents. It is 

 known that where roots are formed there is a pronounced increase 

 in the auxin content. This increase occurs in each of the auxin frac- 

 tions: the free auxin, bound auxin, and the neutral auxin (figure 86). 



Some evidence about the nature of the substances which interact 

 with auxin to control root formation has been brought to light 

 through the observation that leaves strongly promote rooting of 

 cuttings. Van Overbeek et nl (1946) have analyzed the nature of the 

 promotive materials which leaves provide for the cutting, and found 

 that they could entirely replace the effect of leaves by supplying the 



or. 



< 

 < 



(/> 

 a 



UJ 



I- 

 2 

 O 

 O 



X 



< 



600 



400 



200 



o.^^ 



^N Neutral Auxin 



o-o 



^•>- 



8 DAYS 



TIME AFTER CUTTING 



Fig. 86. The changes in content of neutral, bound, and free auxin in the 

 basal ends of chicory root cuttings during root formation (Warmke and Warmke, 

 1950). 



