26 



Auxin has become a general term for a group of compounds which typically 

 induce elongation of shoot cells (Brian et al . , 1955; Weaver, 1972) and 

 they typically produce physiological responses similar to indoleacetic 

 acid (IAA), a naturally occurring growth substance (Brian et al . , 1955; 

 Weaver, 1972; Black and Buchanan, 1980). The auxin discovered by Went 

 was indoleacetic acid, IAA (Salisbury and Ross, 1978) and is considered 

 to be the most common auxin occurring in higher plants. 



IAA was found to be relatively unstable and a search was begun for 

 synthetic compounds of similar chemical constitution and growth -promoting 

 activity. In 1942, work was begun with a series of substituted pheno- 

 xyacetic acids of which 2,4-D is a member (Zimmerman and Hitchcock, 

 1942). Two,4-D is considered to be a synthetic auxin because it causes 

 growth reactions similar to the naturally occurring indole auxins; 

 however, it is more active and persists in the plant for a longer 

 period of time than IAA (Van Overbeek, 1964). With the advent of World 

 War II the idea developed that auxins might be used in high con- 

 centrations to kill enemy crops or limit crop yields (Norman, 1946), 

 and the initiation of tests to study the potency of these new 

 compounds including 2,4-D was begun. Many of these studies were con- 

 ducted in 1944 and 1945 as a part of the activities of the Special 

 Projects Division, Chemical Warfare Service at Camp Detrick in Fredrick, 

 Maryland (Norman, 1946). Publication of this early work was delayed due 

 to wartime security policies (Norman, 1946); however, the June, 1946 

 issue of the Botantical Gazette contained 18 papers describing the 

 results of the Camp Detrick studies. Commercial application of 

 2,4-D began soon after early trials such as those conducted by Blackman 

 (1945) which demonstrated that broad-leaved weeds growing in grain 



