DETECTION AND QUANTITATIVE DETERMINATION 17 



19326). It is best to have controlled temperature and humidity; 

 fluctuations of 0.5°C. and + 1 per cent relative humidity make 

 little difference in most experiments. The laboratories that have 

 such controlled conditions usually maintain the temperature at 

 25°C. and the relative humidity at 90 per cent. If such a 

 laboratory is not available, a thermoregulator will provide 

 temperature control for a darkroom, and a suitable humidity may 

 be obtained by placing the experimental plants under bell jars. 

 Light for the darkroom must be phototropically inactive, which 



o 



means that wave lengths longer than 5,500A. may be used. 

 Ruby glass or filters such as Corning 246 or Schott OG-2 are 

 satisfactory. 



The culture of the seedlings involves certain difficulties, perhaps 

 the greatest of them being that at times the first internode 

 ("mesocotyl" of the older literature — see Avery, 1930) elongates 

 under the coleoptile and by its nutations makes a whole series of 

 plants useless. Numerous factors have been suggested as the 

 cause of this elongation, among them low temperatures (Blaauw, 

 1909), low moisture content of the soil (Noack, 1914), strong 

 carbon dioxide content of the atmosphere (Maria de Vries, 1917), 

 etc. Through the investigations of Lange (1927, 1929), Beyer 

 (19276), duBuy and Nuernbergk (19296), and Hamada (1929, 

 1931) it has been shown that elongation of this internode in 

 Avena can be suppressed by illuminating the seeds during the 

 soaking period (see below) with bright daylight. Rothert 

 (1894, p. 27) had already pointed out that temporary illumination 

 was effective in checking the development of this internode. 

 DuBuy and Nuernbergk (1929a) showed that its elongation can 

 be checked also by heat radiation. 



It has been shown that nutations may occur in the coleoptile 

 (Bremekamp, 1925; Lange, 1925; Pisek, 1926; Beyer, 19276; 

 Lange, 1933), but these have no role in the usual culture diffi- 

 culties. They become apparent only when the plants are put on 

 the clinostat. These curvatures take place in the plane of 

 symmetry of the plant, either away from the seed (e.g., \'ictory 

 oats) or toward the seed {e.g., orien oats). In addition, occasional 

 torsions may appear in the coleoptile (Beyer, 19276; Tammes, 

 1931) ; these have no special significance in the culture of experi- 

 mental plants for hormone-test objects, nor have the photonastic 

 curvatures described by Lange (1933). 



