CHAPTER III 



PREPARATION AND PROPERTIES OF GROWTH 



SUBSTANCES 



Growth substances have been prepared in large amounts from 

 both plant and animal materials. Fungus cultures were used as a 

 source by Nielsen and Boysen Jensen and later by Thimann and 

 others. Human urine was discovered by Kogl and his associates 

 to be a rich source of substances that promote growth in plants. 

 Later it was discovered that maize oil, malt, and yeast are fairly 

 rich sources, and, still more recently, numerous synthetic com- 

 pounds have been found to be quite active in promoting growth. 

 It remains to be shown whether the latter act as true growth- 

 promoting substances or merely influence hormones naturally 

 present in the plant. 



Kogl has proposed the inclusive term auxin for growth sub- 

 stances that bring about cell enlargement; three such auxins 

 have been isolated in pure crystalline form from plant materials. 

 The chemical name auxin and the physiological name growth 

 substance are equally useful and interchangeable terms. 



PREPARATION FROM PLANT AND ANIMAL SOURCES 



Rhizopus, a Source of Growth Substance. — Nielsen (1930a, b) 

 first showed that growth substance could be extracted from the 

 substratum on which either Rhizopus suinus or Absidia ramosa 

 was cultured. Growth substance was formed when Rhizopus 

 was cultured only on a solid medium. His method follows : 



(1) Petri dishes with a diameter of 18 cm. were used, and two 

 pieces of filter paper were placed in each, (2) The dishes were 

 filled with a solution made up of 10 g. glucose, 10 g. ammonium 

 tartrate, 0.5 g. monobasic potassium phosphate, 0.5 g. magnesium 

 sulphate, 10 drops 1 per cent ferric chloride, and 1,000 cc. water. 



(3) The fungus spores were planted and grown at 35°C. for 6 days. 



(4) The fluid substrate together with the liquid expressed from the 



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