Physiological and Anatomical Effects 135 



injury but also much less mobilization of nitrogenous constituents 

 following 2,4-D treatment. 



The interesting suggestion has been made (van Overbeek, 1952) 

 that the accumulation of nitrogen in leaves in the form of amino acids 

 may be responsible in part for the deformities of leaves following 

 auxin applications. Steinberg (1949) has shown that the frenching of 

 tobacco leaves is associated with abnormal accumulation of amino 



UJ 

 O 



cr 



UJ 

 Q- 



100 



V 



^^ 



Nitrogen 



90- 



O 



^ 80 



O 

 O 



fe 70 



I- 



60 



'S 



Phosphate 



yfos... 



"^n, 



Or^ 



y u: 



^.V^. 



^^ii 



Oh, • 



0.1 



0.3 



0.9 mg/l. 



CONC. OF MCPA 



Fig. 62. Changes in mineral content and dry weight of tomato plants after expo- 

 sure of roots to 2-methyl, 4-chlorophenoxyacetic acid (from Rhodes et al, 1950). 



acids, and frenching symptoms appear to be much the same as the leaf 

 deformities caused by auxin. 



Studies of overall changes in nitrogen, potassium, and phosphorus 

 contents of plants have been made (Rhodes et al, 1950). They found 

 that the treatment of plants with MCPA (2-methyl, 4-chlorophe- 

 noxyacetic acid) at increasing concentrations gave quantitative reduc- 

 tions of total nitrogen, potassium, and phosphorus in tomato plants. 

 The decreases they observed (figure 62) were greatest for potassium 



