CHAPTER II 



DETECTION AND QUANTITATIVE DETERMINATION OF 



GROWTH SUBSTANCES 



In demonstrating the presence of growth substances, the 

 coleoptile of the Avena seedhng has been used almost exclusively 

 as a test object. Its structure and sensitiveness to stimuli make 

 it suitable for quantitative tests as well as qualitative demonstra- 

 tions. A minute amount of a growth hormone applied unilat- 

 erally near the tip of a coleoptile brings about increased growth 

 on the side receiving the growth substance, and this produces a 

 growth curvature. The amount of curvature can be used, 

 within certain limits, to indicate the concentration of the appUed 

 growth substance. In a similar way Cephalaria seedlings have 

 been used as quantitative test objects (Soding, 1935a, h). Other 

 methods and numerous other plant organs are equally useful for 

 quaUtative demonstrations (see Figs. 17, 37, 39). 



THE TEST FOR THE PRESENCE OF GROWTH SUBSTANCE WITH 



THE AVENA COLEOPTILE 



The Culture of the Avena Seedling for Use as a Phytohormone 

 Test Object. — A genetically uniform variety of Avena sativa has 

 been used almost universally in the plant-hormone work of the 

 past few years. It is obtainable from Dr. E. A. Akerman of 

 Svalof, Sweden, and is known as siegeshafer, or victory oats. 

 While other uniform strains may be used just as successfully, 

 there is an important advantage in all workers having genetically 

 comparable test material. The variety gul naesgaard is used in 

 the Copenhagen laboratory. 



Culture Conditions. — The generally accepted culture method 

 necessitates a darkroom for growing the Avena seedhngs and for 

 carrying out the quantitative determinations, although Soding 

 (1935a) has recently described a dayhght method. The arrange- 

 ment of such a darkroom has been described repeatedly in the 

 Uterature {e.g., Linsbauer, 1922; Went, 1928a; Nuernbergk, 



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