64 GROWTH HORMONES IN PLANTS 



obtained extracts from the eyestalks of the crustacean Palae- 

 monetes which promoted growth of the Avena coleoptile. Growth 

 substance is often present in foUicle-hormone preparations, but 

 the crystaUized folHcle hormone exerts no effect resembhng that 

 of the plant-growth substance (Kogl and Haagen Smit, 1931, 

 Mitt. I; Harder and Stormer, 1934). 



THE FORMATION OF GROWTH SUBSTANCES 



Lower Plants. — The conditions that influence the formation of 

 growth substances by fungi have been investigated in considerable 

 detail. Nielsen (1930a, b) found that Rhizopiis suinus forms 

 growth substance in the presence of glucose-ammonium tartrate 

 solutions, when cultured on a more or less solid substratum. 

 However, Aspergillus niger does not form growth substances in 

 glucose-nitrate or glucose-ammonium solutions; relatively large 

 amounts are formed in glucose-peptone solutions on a fluid 

 substratum. Boysen Jensen (1932) studied a series of compounds 

 from the point of view of their possible use in the formation of 

 growth substance. Investigations on a series of amino acids 

 yielded the following results : Tyrosin was found to be an excellent 

 growth-substance former; the same is true for two cyclic amino 

 acids, phenylalanin and histidin, and two aliphatic amino acids, 

 leucin and lysin. Glycocoll, alanin, arginin, asparagin, cystin, 

 and prolin were found to be ineffective. The amount of growth 

 substance produced is increased greatly with temperature, ten 

 times as much being formed at 36 to 37°C. as at 22 to 24°C. 

 (c/. Sakamura and Yanagihara, 1932). 



Thimann and Dolk (1933) (see Bonner, 1932) found that 

 growth-substance production by Rhizopus growing on a peptone- 

 dextrose culture medium is greatly increased by aeration; the 

 increase is proportional, within limits, to the extent of the aera- 

 tion. The optimum yield of growth hormone is reached after 

 10 days at a temperature of 35 to 36°C. Its production takes 

 place during the quiescent stage after rapid vegetative growth has 

 ceased. Witte peptone, prepared from fibrin, was superior to 

 Merck's Fleischpeptone, a fact shown later (Thimann, 19356) 

 to be due to the presence of tryptophane in the Witte peptone; 

 the growth substance was identified as heteroauxin. 



The yield of heteroauxin proportionate to the aeration of the 

 cultures (Thimann, 19356) has been explained by the use of 



