128 PHYTOHORMONES 



the same amount of growth. These facts show that there is 

 no direct stoichiometric relationship between the auxin 

 entering and the cell wall constituents upon which it ulti- 

 mately acts. There is not nearly enough auxin to form even 

 a monomolecular film over the surface of the new cell wall 

 which it produces, by which it might affect permeability. 

 Thus auxin acts in some indirect way. This conclusion is 

 supported by the fact that its action is connected with 

 respiration (Bonner, 1933, 1933a, 1936a). Sections of coleop- 

 tiles in solution in nitrogen do not elongate appreciably 

 when auxin is added. Further, the addition of KCN or 

 phenyl-urethane, in concentrations which inhibit respiration, 

 inhibits growth also; if the inhibition is partial it occurs to 

 about the same extent for respiration as for growth. Thus 

 growth does not involve a separate special oxygen uptake, 

 but it is dependent on the presence of the respiration in 

 general. Bonner's earlier view that auxin accelerates the 

 respiration has been shown not to be true (Kogl, Haagen 

 Smit, and van Hulssen, 1936; Bonner, 1936a), since his 

 earlier experiments were carried out with only a partially 

 purified auxin preparation. 



Another attack has been directed towards following the 

 fate of the auxin within the plant (Bonner and Thimann, 

 1935). Determinations of the total amount of auxin in 

 Avena coleoptiles by the chloroform extraction method 

 show that the value of 5.7 units per plant falls, 2 hours after 

 decapitation, to 3.0 units, i.e. 2.7 units have disappeared. 

 The growth which has taken place in this time is 0.79 mm., 

 which, according to the straight growth measurements, 

 would require the addition of 2.9 units. The growth resulting 

 has therefore been strictly proportional to the amount of 

 auxin which disappeared. 



If, however, high concentrations of auxin are applied to 

 the plant, then the growth which results uses up only a small 

 part of the auxin, and most of the rest disappears. Sim- 

 ilarly, if auxin be applied to cut-off coleoptiles without water 

 supply, they do not grow but the auxin continues to dis- 



