Developmental Effects of Auxins 95 



The promotion and inhibition of flowering by auxins have been 

 plotted in this way (Leopold and Thiniann, 1949), and similar curves 

 (<nild be drawn lor fruit growth and leaf growth. 



A leinarkable tlualisin exists in the actions of auxin. Auxin tan 

 either stimulate or inhibit the various growth functions. .Auxins can 

 promote or inhibit the differentiation of buds, promote or inhibit 

 the production of flowers, promote or inhibit abscission, promote or 



O 



h- 



o 



o 

 a: 

 a. 



m 



X 



10 M 



AUXIN CONCENTRATION 



Fig. 46. Ranges of growth responses to auxin (indoleacetic acid) for various plant 

 organs (modified from Thimann, 1937). 



inhibit respiration or activity of some enzymes, promote or inhibit 

 protoplasmic streaming, promote or inhibit the accumulation of cer- 

 tain biochemical plant constituents, and promote either differentiation 

 or dedifferentiation of living cells. In each case, the effect obtained 

 is primarily a function of the effective auxin concentration in the tis- 

 sue. A logical explanation on a biochemical basis of the dualism of 

 auxin effects upon growth is discussed in chapter VIII. 



