Rooting 209 



tice for many years. This method, called marcotting, involves ringing 

 a stem and binding a moist medium such as peat moss around the 

 ringed area. The ring interferes with the transport of auxin and other 

 materials through the stem. Because of the polar nature of auxin 

 transport and because transport can occur even against a large con- 

 centration gradient (as discussed in chapter III), auxin accumulates 

 above the ring and stimulates root formation there. It is probable 

 that other materials which are beneficial to root initiation and growth 

 may also accumulate above the ring. These include sugars, nitrogenous 

 materials, and groAvth factors such as thiamine which is formed in the 

 leaves and is beneficial to root growth (Went et al, 1938). Marcotting 

 is widely used by greenhouse operators for propagation of woody 

 plants. The effectiveness of this treatment has been further improved 

 by application of auxin above the ring to supplement the endogenous 

 auxin (Cooper, 1944). Irradiation with large doses of x-rays also causes 

 rooting above the treated zone (Christensen, 1954). It is probable that 

 this treatment too is effective because of the interference of transport 

 of auxins and other materials. 



Another propagation technique ^vhich utilizes endogenous auxin 

 is layering. Branches are bent to the ground and covered with soil 

 to generate roots. This method of obtaining roots is also improved by 

 ringing and by the addition of auxins above the ring (Gossard, 1941; 

 Floor, "l 951). 



In many instances people have tried to use auxins to iinprove 

 rooting in transplants. These attemj^ts have been singularly unsuccess- 

 ful with only rare exceptions such as the report by Neff and O'Rourke 

 (1951), in which the roots were heavily trimmed back before auxin 

 application. These observations find a ready explanation in that 

 auxins applied to intact roots would be expected to inhibit root 

 growth because of the extreme sensitivity of roots to auxin (cf. figure 

 46). The inhibitory effect would be expected to override any root- 

 forming influence of the treatment. However, when the roots have 

 been severely trimmed back as in the case reported by Neff and 

 O'Rourke, or removed entirely, as is usual with cuttings, then the 

 root-forming effects of auxins can become beneficial. 



Selection of Structure 



Nearly any plant organ is capable of forming roots. Not only 

 stems but leaves, stolons, roots and even flowers and fruits can be 

 rooted (e.g. Balansard and Pellissier, 1942; Warmke and Warmke, 

 1950; Bouillenne and Went, 1933; Erickson and De Bach, 1953). 



Stems are generally an ideal rooting material because they usually 



