Physiological and Anatomical Effects 127 



auxin b was substituted for the indoleacetic acid used in the first 

 report, such a stimulation of respiration was not found. The failure 

 to repeat the respiration observation led to a general loss of interest 

 in the possibility of a respiratory function being involved in auxin 

 action. The field was opened again in 1941 by the work of Commoner 

 and Thimann, who reported that a stimulation of respiration was 



o 

 o 



E 

 o 



o 



c 



T3 



O 

 < 



a. 

 (/) 



UJ 

 DC 



0.00i 0.01 0.1 I 



10 100 1000 MG/L 



CONC. OF AUXIN 



Fig. 57. The relative effects of varying concentrations of auxin (2,4-D) upon 

 respiration (QOo) of etiolated Avena coleoptile and pea stem sections (Kelly and 

 Avery, 1949). 



associated with the auxin stimulation of growth if a supply of organic 

 acids was made available, malic acid being particularly effective. Since 

 that time, several laboratories have confirmed the observation that 

 auxins stimulate respiration in the same concentration ranges that 

 stimulate growth. However, the inhibition of growth with auxins is 

 not necessarily associated with similar inhibitions of respiration 

 (Smith, 1951). 



