A microphotometric study of various Feulgen-stained gametophytic and sporophytic nuclei of Tradescantia paludosa was made to test the hypothesis that DNA is maintained in multiples of a basic unit within all cells of an organism. A multiple relationship was found in all tissues analyzed. The lowest amount of DNA was found in gametophytic nuclei, approximately twice and four times this amount in sporophytic nuclei, and approximately three and six times this amount in endosperm nuclei. Intermediate amounts of DNA were found only in tissues presumably undergoing an interphase synthesis of DNA preceding either cell division or endomitosis. It is concluded that within the limitations of present methods of measurement, DNA amounts show a quantitative behavior which supports the "constancy" hypothesis. Such quantitative stability of DNA gives support to the concept that DNA is associated with the stable elements of the gene.