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The Eastman Chromagram apparatus was employed in thin-layer chromatographic studies involving United States species of Polymnia (Compositae). Certain technical modifications of this apparatus were made in an attempt to more efficiently saturate the chamber with vapors of the eluents. Results indicated that a critical level of reproducibility could be achieved only with modified apparatus, which included the insertion of saturated "fT'-shaped filter paper, with a glass rod across the base of the "| j " , all held securely between the two glass plates by additional clips.