128 Fundamentals of Auxin Action 



An interesting difference in sensitivity of the respiratory systems 

 of monocots and dicots has been demonstrated by Kelly and Avery 

 (1949). They found that respiration of pea stems is stimulated by 

 concentrations of auxin over one hundred times more dilute than 

 those needed to stimulate respiration in the Avena coleoptile. The 

 greater respiratory sensitivity of the pea as shown in figure 57 is 

 strongly reminiscent of the greater herbicidal sensitivity of dicots in 

 comparison with monocots. 



c 

 o 

 o 



*♦— 



o 



to 

 o 



160- 



140 



120 



< 



or 100 



CL 



if) 



UJ 



8Qj^ 



Respiration 

 • 



10 



2 O 

 CD 



10'® 10'^ 10"® 10"* 10"^ 10"^ M 



CONC. OF AUXIN 



Fig. 58. The influence of auxin (indoleacetic acid) on growth and respiration of 

 corn coleoptile sections. Growth is expressed as mm. of growth per 10 sections 

 6 mm. long, and respiration as relative oxygen consumption (French and Beevers, 

 1953). 



There are many and diverse observations of increases in respira- 

 tion subsequent to auxin applications to plants. A few general ex- 

 amples that might be cited from applied studies are increases of 

 respiration rate of fruits following auxin application to prevent ab- 

 scission (Smock and Gross, 1947), and increases in respiration of plants 

 following sprays for herbicidal effects (Brown, 1946). 



The interesting question arises concerning the relationship be- 



