Plant Qrowth'Suhstances 



laboratory. The synthesis of the auxins is a difficuh problem 

 in chemistry. 



At this point I may make a digression for the benefit of 

 those whose ideas of chemistry are based on the reading of 

 popular novels involving a secret chemical formula, In 

 chemistry, a formula is not a recipe, but is an exposition of 

 the number and kinds of atoms comprising a substance, show- 

 ing also the way in which the atoms are arranged in relation 

 to one another. Before a natural substance can be imitated in 

 the laboratory, it is necessary to know the exact "configura- 

 tion" of the molecule of the substance; knowledge of the 

 formula, however, is far from being all that is necessary to 

 enable even an expert chemist to make the substance on the 

 spot. Those who are interested can find the formulae of the 

 auxins on page 113.^ 



In urine there is often a third growth-substance, the 

 existence of which was discovered in a curious way by Fritz 

 Kogl and others, of Utrecht. They found that it was not 

 always possible to extract auxin-a from the mixed urines of a 

 hospital. They therefore concentrated their attention on an 

 "especially appreciated source" — the urine of an eighteen- 

 year-old youth, which had been found by the oat test to be 

 four or five times as active as ordinary urines. An isolation 

 procedure applied to this urine led to the production of a 

 very small quantity of crystals of a substance quite different 

 from either of the auxins, though practically as eflfective in 

 causing cell-elongation in seedling oats. The nature of this 

 substance was a puzzle, but some hints were available, and 

 finally the "new" substance was definitely established to be 

 indole-acetic acid, which was already well known to chemists, 

 but was not then known to be a growth-regulating substance. 

 This shows that if you enter hospital, you never know what 

 purpose you are likely to serve ! 



Later, indole-acetic acid was found to be present in very 



^The formulae of vitamins Bj and C can also be found on pages 115 and 116. 

 These substances are now made artificially, and are on sale. 



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