For the Layman 



minute amount in yeast, from which it was laboriously 

 isolated after more than a hundred and fifty separate treat- 

 ments had been made upon three hundredweights of yeast 

 in portions of a kilogram (about two pounds) at a time. 



The story of these, and other, discoveries has been racily 

 told by Dr. Kogl and his collaborators in the"Zeitschrift fiir 

 physiologische Chemie," vol. 228, of 1934. Regarding the 

 role of chance in the sequence of isolation of the auxins and 

 of indole-acetic acid, I cannot do better than give the words 

 (translated, of course) of Dr. Kogl and Dr. Kostermans from 

 page 116: 



"It was a lucky accident that from urine, which contained 

 both the growth-substances [i.e., auxin, and indole-acetic 

 acid], we isolated the "real" auxin first. If our attempts to 

 isolate the active substance had first of all led to the finding 

 of indole-acetic acid, probably no one would have taken the 

 trouble to separate the active substance [auxin] existing in 

 the residual liquors. Having acquired the knowledge that 

 yeast and other lowly plants form a substance capable of 

 producing cell-elongation, and identical with indole-acetic 

 acid, one would probably have been content with that, and 

 any variation in behaviour displayed by growth-substances 

 in cereals [oats, especially] would have been put down to 

 the existence of substances only incidentally present. The 

 existence of auxins a and b would, most likely, have re- 

 mained unsuspected for a considerable time." 

 Even now, it is not known why indole-acetic acid and the 

 auxins behave so similarly when applied to the decapitated 

 seedling oat and in some other tests of growth-promotion and 

 regulation. It is usually assumed that substances that display 

 similar physiological behaviour are at least related chemically, 

 but between the auxins and indole-acetic acid there is no 

 obvious similarity whatever. All three substances occur in 

 urine because they are derived from articles of diet, but the 

 origin of urinary indole-acetic acid is quite different from the 

 origins of the auxins. 



An important practical consequence arose from the dis- 



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