25 

 (1948) and Center and Spencer (1981). GA 3 also markedly inhibited vege- 

 tative reproduction and induced profuse flowering. Watson et al . (1982) 

 reported similar effects on leaf morphogenesis, vegetative repro- 

 duction, and flower production when GA 3 (0.00 to 0.05 mg/1 ) was applied 

 to waterhyaci nth roots. However, at concentrations greater than 0.05 

 mg/1 GA 3 , higher rates of production of inflorescences and daughter roset- 

 tes were observed. Watson et al . (1982) also reported an increase in 

 stolon elongation at GA 3 concentrations up to 0.03 mg/1. However, above 

 0.05 mg/1, GA 3 caused a decrease in stolon length and suppressed stolon 

 production at 1.0 mg/1. Foliar application of GA 3 at a rate of 6.0 g/ha 

 was also shown to inhibit the formation of float-type leaves although 

 apparently not as dramatically as when GA3 was applied to the roots 

 (Pieterse et al . , 1980; Pieterse and Roorda, 1982). 



2 ,4-Di chl orophenoxyaceti c Aci d 



History 



The chemical, 2,4-dichlorophenoxyacetic acid (2,4-D), is a systemic 

 herbicide which is routinely used for the control of broadleaf weeds 

 (Weed Science Society of America, 1979). The synthesis of 2,4-D was a 

 result of research initiated in the 1880's by Julius Sachs, a German 

 botanist, who suggested the presence of plant organ-forming substances 

 (Salisbury and Ross, 1978). The existence of naturally occurring 

 compounds which stimulated plant growth was first demonstrated by 

 Seubert in 1925 (Weaver, 1972). In 1926, Went developed a procedure for 

 quantitative isolation of growth-promoting compounds which stimulated 

 their isolation and identification. Went was also the first to 

 call these compounds auxins (Weaver, 1972; Salisbury and Ross, 1978). 



