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Degree Name

Doctor of Philosophy




The effect of 2,4-dichlorophenoxyacetic acid on the composition and activity of dandelion roots was studied, using three concentrations (120, 480, and 1920 ppm.) of 2,4-D in aqueous sprays. Root samples were taken before treatment and at five day intervals for 25 days after treatment. Determinations were made of the content of reducing sugar, sucrose, dextrin, levulin, alcohol soluble nitrogen, and protein nitrogen in the roots. Measurements of the rate of respiration were also made;The reducing sugar content was increased rapidly by the treatments, but later decreased towards the level of the control. It was found that the loss could be roughly accounted for by the increased rate of respiration, indicating little if any utilization of sugars for growth response;Respiration rates were increased with the 2,4-D, the low concentration giving only a temporary stimulus with a return to normal, possibly because of the small quantity of 2,4-D, while the medium concentration gave the greatest increase which remained high as long as the roots were alive. The highest concentration caused a temporary increase followed by a decrease to normal similar to the response to the light treatment, but the decrease was probably due to a toxic effect of the high concentration;The total soluble nitrogen content of the roots was increased with the light and medium treatments, but it was unaffected by the heavy treatment. The medium treatment also caused an increase in the protein nitrogen content, but the light and heavy treatments did not show any marked effect on this fraction;A comparative test of 2,4-D with kerosene and sodium chlorate showed that 2,4-D and kerosene were equally effective in decreasing the carbohydrate reserves and in increasing the rate of respiration, while sodium chlorate was less effective;From the results of the studies it appears that the action on dandelion of 2,4-D in herbicidal concentrations is principally the destruction of carbohydrate reserves, with most of the loss being accounted for by increased respiration. (Abstract shortened by UMI.)



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Lowell W. Rasmussen



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106 pages