Plant Qrowih'Suhstances 



Auxin-a is very stable towards acids, but is readily decom- 

 posed by alkalis. Auxin-b is decomposed by both acids and 

 alkalis, whereas indole-acetic acid, though hydrolyzed by 

 acids, is very stable towards alkalis. These properties were 

 made use of by Kogl, Haagen-Smit, and Erxleben (1934) as 

 showing that the growth-hormone in the tips of oat seedhngs 

 was probably auxin-a. 



Auxin-a lactone, distilled with potassium hydrogen sul- 

 phate, yielded a substance probably identical with auxin-b. 

 (Kogl, 1935). 



Kogl (1938) has pointed out: "The formula of auxin-a 

 contains seven asymmetric carbon atoms; any organic 

 chemist knows what that implies. Suppose it were possible 

 on starting from inactive material to produce an auxin-a of 

 the correct structure, even then the product would consist of 

 a mixture of 64 racemates, requiring to be resolved into 128 

 optical enantiomorphs. And only one component of that 

 mixture of stereoisomers would be identical with auxin-a." 



Synthesis of auxin-glutaric acid (containing four asymmetric 

 carbon atoms) has been accomplished, and a product identical 

 with the natural derivative was obtained after about 300 frac- 

 tionations, so that definite proof of the constitution of a 13- 

 carbon-atom part of auxin-a and -b has been obtained (Kogl 

 (1938) ). 



Vitamins 



Vitamin B^ 



Although when this book was first planned, the idea of a 

 synthetic plant growth-substance did not extend beyond the 

 phenyl, indolyl, naphthyl, and related compounds introduced 

 into horticultural use about 1935, at least two of the vitamins, 

 and perhaps other synthetic substances, have or are likely to 

 have considerable horticultural importance. (P. 80). 



The complete synthesis of vitamin B^ was accomplished, or 

 at least published, almost simultaneously in 1937 by American, 

 British, and German workers. The question of priority has 

 been discussed in letters from Robert Robison and A. L. 



11+ 



