Rooting 213 



is the polarity ot root tormation. Since the movement of auxins in 

 the stem is from the apex to the base, it is not surprising that root 

 formation takes place preferentially at the base of the cutting where 

 the auxins accumulate. Went (1936) has shown, however, that when 

 high enough concentrations of auxin were applied to cuttings, some 

 roots would be formed at the apex of the cutting. It is assumed that 

 this phenomenon is due to a nonpolar auxin translocation at the 

 Iiigh concentrations. 



The role of leaves in rooting has already been described as pro- 

 viding certain nutritive materials beneficial to root formation. The 

 dependence of rooting on the carbohydrate supply has been amply 

 demonstrated (Pearse, 1943), and other materials such as vitamins and 

 nitrogenous materials are supplied by the leaves as well. The bene- 

 ficial effect of leaves may be accentuated by spraying a sugar solution 

 on the foliage (Langston, 1954). It seems evident that leaves are bene- 

 ficial to the rooting response to auxin for nutritive reasons. 



The presence of buds on a cutting has a strongly promotive effect 

 on rooting. Van der Lek (1934) found that root formation was almost 

 absent if all the buds were removed from woody cuttings or if all the 

 buds were entirely dormant. The same beneficial effect of buds has 

 been found in auxin-treated cuttings. The application of auxin has 

 not been found to entirely replace the presence of buds in causing 

 root formation (Went and Thimann, 1937, p. 189). However, the 

 basipetal polar transport of the substances from the buds strongly 

 suggests that at least some of the effect is due to auxin production in 

 the bud. It is interesting to note that O'Rourke (1942) found that in 

 cuttings from some species at least flower buds strongly inhibit rooting 

 in contrast to the promotive effect of vegetative type buds. It is 

 possible that the inhibitory effect of flower buds may be related to 

 the effects of flowers in removing auxin polarity described in chapter 

 III. It has been pointed out by Dore (1953) that root and stem 

 cuttings of most plant species are singularly poor at generating new 

 roots if they are taken from the plant when flower buds are present. 

 It seems that buds influence rooting through some hormonal influence 

 rather than through nutritive effects. 



Inorganic materials are influential in rooting, and most important 

 among them appears to be the soluble nitrogen fraction in the plant. 

 While some quantities of nitrogen are very beneficial to rooting, large 

 quantities are very inhibitory. The lower the carbohydrate level of 

 the plant, the greater are the inhibitory effects of high nitrogen levels 

 (Pearse, 1943, 1946). Another inorganic nutrient which has a strong 

 influence on rooting is boron. A lack of this nutrient in the rooting 



