204 Auxins in Agriculture 



cuttings with sugars and nitrogenous compounds. In figure 87 it can 

 be seen that there is a cjuantitative increase in roots formed in red 

 hibiscus cuttings with the presence of leaves, and that the promotive 

 effect can be entirely replaced by sucrose plus ammonium sulphate. 

 It can also be seen that without the addition of auxin (indolebutyric 

 acid) rooting is essentially absent whether these nutrients are pro- 

 vided or not. These same workers convincingly demonstrated that 

 leaves do, in fact, supply the cutting with the same types of nutrient 

 materials which had been added in the experiment described, namely 

 sugars and soluble nitrogenous materials. Chemical analysis of cuttings 

 with various numbers of leaves revealed that the content of reducing 

 and non-reducing sugars and of soluble nitrogenous materials in the 

 cutting was dependent upon the number of leaves. The nutritive 

 effects of leaves are illustrated in figure 88. 



Van Overbeek et al (1946) stated that organic forms of nitrogen 



e> 



V- 



O 



(T 

 UJ 

 Q- 



q: 

 o 



h- 

 o 

 o 



Auxin + Sucrose +{NHJ,SOa 



Sucrose + (NH4)2S04 



Control 



NUMBER OF LEAVES 



Fig. 87. The effect of leaves on cuttings of red hibiscus in permitting stimula- 

 tion of root formation by auxin (2000 mg./l. indolebutyric acid). The promotive 

 effects of leaves can be entirely replaced by supplying 4 per cent sucrose and 0.1 per 

 cent ammonium sulphate (van Overbeek et al, 1946). 



