12 



Fundamentals of Auxin Action 



et al (1945), Blackman (1945), Nutman et al (1945) and Kraus and 

 Mitchell (1947). The herbicidal uses of growth regulators are by far 

 the most widespread. It is estimated that 60,000,000 pounds of 2,4-D 

 are manufactured annually in the United States and perhaps 50,000,- 

 000 acres of land are treated with this herbicide alone. The dramatic 

 rise in the production of 2,4-D since its first release from secrecy in 

 1945 can be seen in figure 2. 



YEAR 



Fig. 2. The rise in the annual manufacture of 2,4-D in the United States since the 

 open publication of its herbicidal effects in 1945. Data of U. S. Tariff Commission. 



The development of an understanding of auxins in plant growth 

 has effected startling advances in physiological and technological 

 knowledge. Although the understanding of theoretical physiology has 

 in many respects been outstripped by the technology of the applica- 

 tion of auxins, still that is where the foundations of the entire field 

 were laid, and the only sound basis for efficient progress lies in the 

 advances of fundamental physiological understanding. 



