1. The Feulgen reaction maintains its specificity after each of the nine different fixatives used; of the cell components it stains the chromatin only.2. The intensity of the staining reaction of the root tip cuticle by the Feulgen technique usually varies with the fixation as does that of the chromatin.3. For each of the other stains employed (Heidenhain's iron alum-hematoxylin, crystal violet-iodine, and safranin-iodine) the stainabilities of the different ceil structures are conditioned directly by the fixative.4. Crystal violet-iodine and safranin-iodine exhibit no consistent differences in their selectivity for the various cell organs after any of the fixatives.5. After certain fixatives the hydrochloric acid treatment used for the partial hydrolysis of the thymonucleic acid for the Feulgen reaction (N HCl at 60°C. for 20 minutes) affects the relative staining capacities of plastin and chromatin, when the iron alum-hematoxylin, crystal violet-iodine, and safranin-iodine stains are used.6. Only the Bouin and Navashin-fixed material is affected by hydrochloric acid treatment in the reaction to iron alum-hematoxylin: in both the chromatin loses some of its staining capacity; in the latter the stainability of the nucleoli is increased as well.7. The effects of treatment with hydrochloric acid an the staining reactions of crystal violet-iodine and safranin-iodine is quite pronounced for several fixatives: chromatin stainability is increased after modified Erlicki, decreased after Navashin and copper bichromate, and lost after Bouin fixation; nucleolar stainability is acquired after copper-chrome-propionate, increased after Navashin, copper bichromate, and chromic sulfate-formaldehyde, decreased after modified Erlicki, and decreased or lost after nickel-chrome-propionate fixation.8. Copper-containing fixatives that render the nucleoli stainable with crystal violet-iodine and safranin-iodine cause the nucleolar peripheries to stain darker than the Centers, while after hydrochloric acid treatment this reaction is reversed, the centers staining darker than the peripheries.9. In some preparations mitotic nucleoli differ from intermitotic nucleoli in their reactions to stains, which would seem to indicate that the nucleolus undergoes some chemical or physical change at the initiation of mitosis.10. Evidence is presented in support of the view that plastin, as well as chromatin, occurs in the form of granules in the reticulum of the intermitotic cell.11. Nucleoli, which are mordanted by copper-containing fixatives only if the pH is above 4.0, are but little affected in regard to their stainability by subsequent treatment with hydrochloric acid of a much lower pH.12. Mitochondria, which are usually dissoived out by the more acid fixatives, are not affected by treatment with normal hydrochloric acid after fixation.I want to express my appreciation to Dr. Conway Zirkle for suggesting this problem, as well as for his help and advice throughout the course of the investigation.