Development of Knowledge of Auxins 1 1 



a much better understanding of many physiological phenomena in 

 plants, but also it has given the agriculturist a set of new tools for use 

 in plant culture. The technological applications of auxins have been 

 expanded extremely rapidly. Unfortunately a very great number of 

 workers have launched into research on the uses of auxins without first 

 obtaining a background in the fundamentals of auxin action in plants. 

 This has led to much confusion, a large amount of misinterpretation 

 of results, and a lack of understanding of what intelligent steps can 

 be taken to obtain desired effects. This confusion, caused in consider- 

 able degree by lack of background on the part of research workers, 

 has brought some disrepute to the agricultural uses of growth regula- 

 tors. Now that the early flare of expansion of agricultural uses is ap- 

 parently past, it is hoped that further research concerning the uses 

 of these physiologically active coinpounds will be carried out with a 

 more comprehensive background in physiology. 



The use of auxins in agriculture started very modestly. The first 

 application to be discovered was in the rooting of cuttings. In 1934, 

 Went published the results of his experiments which showed that 

 auxins could be used to stimulate root formation. This discovery led 

 to a great many studies of the uses of auxins in plant propagation. At 

 present there are several commercial preparations on the market for 

 this use, and when they are used wisely they are very effective indeed. 



In 1935, Zimmerman and Wilcoxon discovered that alpha-naphtha- 

 leneacetic acid and some chlorinated phenoxyacetic acids are very 

 strong auxins. The activity of these and particularly of 2,4-dichloro- 

 phenoxyacetic acid (Zimmerman and Hitchcock, 1942) was so much 

 greater than the compounds which had been used previously, that the 

 way was opened for some of the greatest practical uses of auxins. 



Discoveries of further practical uses followed in quick succession. 

 In 1936, Gustafson demonstrated that some fruits could be set parthe- 

 nocarpically with auxins. Trials of this technique on commercial fruit 

 crops have led to profitable uses in two crops: tomatoes and figs. In the 

 same year, 1936, the discovery by LaRue that abscission of leaves could 

 be delayed led ultimately to the application of auxins to prevent pre- 

 mature abscission of tree fruits. In 1942, Clark and Kerns found that 

 flowering could be induced in pineapple by auxins. The pineapple 

 industry in Hawaii and in Puerto Rico quickly took up the use of 

 auxin sprays to bring about uniform flowering in each field. During 

 World War II, the herbicidal properties of the phenoxyacetic acid 

 derivatives were carefully studied under cover of military secrecy 

 both in England and in the United States. These studies were first 

 legitimately published in 1945 and 1947 by four research teams: Slade 



