NO. 20 GROWTH SUBSTANCE BURKHOI.DER AND JOHNSTON I3 



depends upon the kind of growth substance present (Van Overbeek, 

 1936). When auxin a is appHed unilaterally to Avena coleoptiles, 

 curvature is less in light than in darkness, but when 3-indole acetic 

 acid is used, the curvatures are the same in light and in darkness. 

 Van Overbeek (1936a) has reported, furthermore, that exposure to 

 the red plus infrared radiation of an ordinary darkroom lamp causes a 

 decreased growth substance content in the tips of Avena. 



Experimental results reported here indicate marked decreases in 

 growth-promoting properties of irradiated tissue and of agar blocks 

 containing growth substance. When so great losses occur under the 

 influence of controlled radiation as mentioned, it is not probable that 

 translocation of the active material should play any prominent role 

 in growth phenomena at the same time. Under some circumstances, 

 e. g., low light intensity, it may be that more growth substance is 

 moved than is destroyed in the plant. It appears from the experi- 

 mental evidence presented in this paper that light of high intensities 

 has a destructive or inactivating action on plant growth substance, 

 which is of great importance for phototropism and morphogenesis. 



LITERATURE CITED 

 Avery, G. S., Jr. 



1935. Differential distribution of a phytohormone in the developing leaf of 



Nicotiana, and its relation to polarized growth. Bull. Torrey Bot. 

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 BoYSEX Jensen, P. 



1933- Uber die durch einseitige Lichtwirkung hervorgerufene transversale 

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1936. iJber die Verteilung des Wuchsstoffes in Keimstengein und Wurzeln 



wahrend der phototropischen und geotropischen Kriimmung. Kgl. 

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BURK HOLDER, PaUL R. 



1936. The role of light in the life of plants. Bot. Rev., vol. 2, pp. 1-52, 

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 DoLK, H. E., and Thimann, K. V. 



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1933. IJber Wachstum und Phototropismus von Avena sativa. Rec. Trav. 



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