Synthesis 



sein test indicated, and by the sensitive methods of plant 

 physiology, it can be shown that by virtue of their content of 

 "auxins", most urines are capable of affecting cell-growth in 

 plants. Phenyl-acetic acid is also capable of affecting plant 

 growth, as are a number of homologues. 



Effect on Plant Growth 



Looking back, it seems a little remarkable that more 

 curiosity was not shown by agriculturists and plant physiolo- 

 gists about the effects on plant growth of the products of 

 protein breakdown. From consideration of the universal 

 esteem in which composts and animal manures have always 

 been held, it might reasonably have been deduced that some- 

 thing was present in them that was not explainable in terms of 

 N,P,K, and "humus". The fact is that elemental chemistry 

 (with some quasi-mystical appeals to the unknown humus) has 

 held this field. Investigation of the ability of certain products 

 of protein breakdown to regulate growth in plants began 

 without references to the origin of the substances ; but when 

 the composition of "heteroauxin" had been ascertained, that 

 substance was found to be identical with the long-known 

 decomposition-product, indole-acetic acid. 



Already a considerable number of substances shown to 

 possess growth-regulating properties in plants have been 

 found to occur naturally, and many have been synthetized. A 

 description of the chemistry alone of these substances would 

 fill a small book, which would be out of date as soon as printed. 

 Therefore, no attempt will be made here even to list the 

 recorded growth-regulating substances, but an idea will be 

 given of the synthetical preparation of some representatives 

 of each complex group, excepting only the active phenyl 

 compounds such as phenyl-acetic, phenyl-propionic, and 

 fl//o-cinnamic acids. Interested chemists, having consulted 

 the standard textbooks, will find more recent details in the 

 substantially complete references at the end of this chapter. 

 Being intended to introduce some physiological, as well as 

 chemical, notions, the account is not presented in an entirely 

 logical chemical order. 



99 



