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A new stain-kative method for chromosomes, namely acetic-orcein, is described, which gives results that are equally good in fresh and permanent preparations. A 45% acetic and 1% orcein content is recommended as a standard solution. For salivary glands of Drosophila a 2% stain gives the best results, and with the two species D. melanogash and D . miranda the acetic strength has been raised to 70% with advantage. The addition of chloroform proves necessary for hardening in species of Sciara. Acetic-orcein is equally good for rapid chromosome counts. For root tips the addition of 1 cc. of N HC1 solution to 10 cc. of the standard solution to-