Lecture 2 



39 



Micronutrient Elements 



to normal illumination. It may be added that short 

 wave light seems to increase the rate of breakdown of 

 auxin. 



The low zinc plants with a low auxin content had 

 a higher peroxidase activity than that of the plants 

 with a larger zinc supply and Dr. Skoog postulated in 

 accordance with the view originally proposed at the 

 California Institute of Technology on the basis of 



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M * • U It 20 t* tt 52 



TIME IN DAYS 



Textficure 5. — Tomato plants grown in 

 solutions with and without an adequate supply 

 of zinc. Response in stem elongation follow- 

 ing addition of zinc to a zinc deficient culture 

 is clearly evident. Curve I, plants originally 

 supplied with 0.046 mg. per liter Zn; Curve 

 II. 0.01 mg. Zn: Curve III, no added Zn. 

 (From Skoog, 1940). 



other types of experiments, that the destruction of 

 auxin was accelerated by the increase of peroxidase 

 activity. Later Bean in our laboratory made further 

 experiments relating to this question and also found 

 a relation between zinc and the peroxidase and catalase 

 activities of the plant tissue. 



