50 GROWTH HORMONES IN PLANTS 



After the usual fractionation with benzene the active syrup was 

 heated eight times with xylene at water-bath temperature; the 

 xylene extracts were combined and evaporated to dryness in a 

 vacuum. The residue (500 mg.) had an effectiveness of 1,200,000 

 AE per milUgram and contained about 20 mg. of 3-indole acetic 

 acid. Crystals formed in this crude oil after it had been in the 

 refrigerator for a day; these were siphoned off and washed several 

 times with a little cold chloroform. The color reaction of this 

 crude crystallate with ferric chloride-hydrochloric acid was 

 intense, but the effectiveness amounted to only about 2,000,000 

 AE per milligram. (6) Recrystalhzation from chloroform 

 increased the purity and physiological activity too slowly, so 

 the crystallate was boiled twice with benzene, and the benzene 

 solutions discarded. Then the insoluble matter was recrystal- 

 lized twice from water. There resulted 9 mg. of a product with 

 a melting point of 163. 5°C. and an effectiveness of 17,600,000 AE 

 per milligram. 



PROPERTIES OF GROWTH SUBSTANCES 



The Structural Constitution of the Auxins. — The structure of 

 the foregoing auxins is now well-known (Kogl, 1935, Mitt. XIV). 

 They are all monobasic acids and have one double bond. Auxin a 

 forms a lactone with the same empirical formula as auxin h. 



Auxentriolic acid (auxin a) is a monocychc trihydroxycar- 

 boxylic acid, with one double bond, and has the structural 



formula 



CHa CH 



CH: 



CH— CH— CH2— CH3 



H H H 



C CH2— C — C COOH 



OH OH OH 



Auxenolonic acid (auxin h) is a monocyclic hydroxyketocarbox- 

 yUc acid, with one double bond, and has the structural formula 



CH2 V ^^' 



CH3— CH2— CH— CH CH— CH— CH2— CH3 



\ /h 



CH^C— C CHo— CO— CH2— COOH 



OH 



