The fleshy hips of the briar rose, Rosa rugosa were cultured on a modified medium developed by Gamborg (1963) to produce callus and suspension cultures. These cells were very light, almost white. Reduced ascorbic acid, determined by the 2,6-dichlorophenolindophenol titration method, was found in the suspension cultures. This finding prompted an investigation into culture techniques for obtaining an optimum concentration of ascorbic acid. During the growth of the cells, the pH rose and ascorbic acid concentration increased after the sixth day. Age of culture was also an important factor as cultures older than three or four weeks contained virtually no ascorbic acid. Possible precursors of ascorbic acid in plants were added to cultures and their effect on the ascorbic acid level was determined over a period of twenty-four hours. D-glucose, D-(-)-levulose, D-galactose and D-glucurono-ɣ-lactone caused no increase. L-gulono-ɣ-lactone brought about a slight increase and a comparatively large increase was obtained with L-galactono-ɣ-lactone. Confirmation for the latter was obtained using the 2,4-dinitrophenylhydrazine method to rule out the possibility or microbial contamination and to be sure that another metabolite was not responsible for the increased reducing capacity of the system. Omission of myoinositol from the vitamin solution of the medium decreased total cell yield but had no effect on the level of ascorbic acid. Decreasing the sucrose content of the medium by one-half caused a sharp decrease in ascorbic acid concentration, indicating that an adequate supply of sugar is a prerequisite for optimum production of ascorbic acid. Growing liquid suspensions under controlled illumination resulted in increased ascorbic acid values with each successive transfer; however, total cell yields decreased each time. In addition, there was no evidence of chlorophyll production in the cultures. This exploratory work shows that ascorbic acid is present in the tissue culture of Rosa rugosa. Therefore, tissue culture may be useful for elucidating the complete pathway for ascorbic acid production which is as yet still unclear. This information coupled with the effects of altering the physical environment of the cells may direct cultures of Rosa rugosa to produce ascorbic acid in quantities that would make its recovery industrially attractive. / Land and Food Systems, Faculty of / Graduate