784 



PLANT GROWTH 



lO 



12 3 4 



Concentration of arsenite 



2 4 6 



Concentration of fluoride 



Fig. gB. Pea stem sections 

 in arsenite and fluoride. 

 Arithmetical plot. Note 

 no growth promotion at 

 any concentration. From 

 Christiansen and Thimann, 

 1950a. 



D 



Fig. gC.Peastemsections in 

 arsenite. Logarithmic plot. 

 Note almost linear propor- 

 tionality. The point marked 

 H2O at left shows elon- 

 gation of control without 

 auxin. From Thimann and 

 Bonner, 1949. 



10" 



10"'' 10"^ 3x10"^ 10"^ 10^ 



Molar concentration of arsenate 



3x10' 



Fig. 9D. Growth rates pre- 

 vailing at the end of 24 

 hours compared with total 

 elongation, in sodium arse- 

 nate. A. pea stem sections 

 in lAA (i mg/1); white 

 circles, with sucrose; black 

 circles, no sucrose. B. pea 

 root sections in sucrose. 

 From Audus, 1952. 



