46 GROWTH HORMONES IN PLANTS 



9. High-vacuum Distillation. — The concentrated syrup was 

 distilled as slowly as possible in portions of 400 to 800 mg. in a 

 high vacuum (at 0.005 to 0.02 mm. mercury). As a rule, four 

 or five fractions were obtained, (a) The first distillate which 

 passed over at the temperature of the bath (below 125°C.) had 

 an average effectiveness of 2,500,000 AE per milligram and gave 

 no crystals of the active auxin. (6) The distillates that passed 

 over at 125 to 135°C. contained the largest part of the active 

 substance and showed an average effectiveness of 9,200,000 AE 

 per milligram (3,100,000 to 24,000,000 AE). In these middle 

 fractions, active crystals separated out after remaining several 

 days in the refrigerator. Occasionally it was necessary to cool 

 with an acetone-carbonic acid mixture; these crystals were 

 filtered off and could be purified further, (c) At a water-bath 

 temperature of 135 to 150°C., very active fractions sometimes 

 were obtained (the values fluctuated between 120,000 and 

 23,700,000 AE per milligram); these formed crystals. The 

 residue remaining had an average effectiveness of 1,100,000 AE 

 per milligram. The amount of the active middle fractions 

 averaged 179 mg. (89 to 336 mg.). The auxin at this point was 

 five thousand times concentrated. 



10. Purification of the Crude Crystallates. — The syrup contain- 

 ing active crystals (the middle fraction) was siphoned off; the 

 crude crystals had an effectiveness of 21,000,000 AE per milli- 

 gram. They could be purified further by recrystallization. 



Six recrystallizations with a mixture of ligroin and ethyl 

 alcohol (1:1) yielded crystals with a melting point of 196°C. 

 and an average effectiveness of nearly 50,000,000 AE per milli- 

 gram. These crystals were auxin a. 



Four recrystallizations with 40 per cent acetone gave crystals 

 with a melting point of 173°C. and an average effectiveness of 

 about 35,000,000 AE per milligram. The crystals obtained in 

 this way were the lactone of auxin a [the designation auxin a 

 was not introduced until auxin h was discovered (Kogl, Haagen 

 Smit, and Erxleben, 1933, Mitt. VII)]. 



Maize Oil, Malt, and Other Sources of Auxenolonic Acid 

 (Auxin b). — Both auxin a and auxin h have been prepared from 

 maize oil and malt (Kogl, 1933; Mitt. VI; Kogl, Haagen Smit, 

 and Erxleben, 1933, Mitt. VII; Kogl, Erxleben, and Haagen 

 Smit, 1934, Mitt. IX; Kogl and Erxleben, 1^34, Mitt. X), also 



