. Cell heredity. Cytogenetics. 318 CELL HEREDITY In larvae of Drosophila rcplcta. the cells of the salivary gland grow rapidlv during the last few days before pupa formation. During the period of the experiment to be described, the nuclear and cytoplasmic volumes tripled, and the nucleolus doubled its volume and RNA content. Larvae selected for uniformity were fed for two hours with adenine-C''*, and then removed to a nonradioactive food source, prior to fixation at various times. The specific activities of RNA in nucleolus, chromatin, and cytoplasm were determined by grain-counting on autorad
. Cell heredity. Cytogenetics. 318 CELL HEREDITY In larvae of Drosophila rcplcta. the cells of the salivary gland grow rapidlv during the last few days before pupa formation. During the period of the experiment to be described, the nuclear and cytoplasmic volumes tripled, and the nucleolus doubled its volume and RNA content. Larvae selected for uniformity were fed for two hours with adenine-C''*, and then removed to a nonradioactive food source, prior to fixation at various times. The specific activities of RNA in nucleolus, chromatin, and cytoplasm were determined by grain-counting on autoradiographs of sectioned material. The results indicate (Figure ) that RNA syn- thesis, as measured by the uptake of adenine, proceeds faster in the nucleolus than in any other fraction and, consequently, that neither chromosomal nor cytoplasmic RNA can be the source of all nucleolar RNA. No other information about transfer of label between chromo- ^ ^''**>'1t^. 11-7a FIGURE Distal end of salivary chromosome C of Rhynchosciara angelae showing localization of DNA by means of autoradiography of tritiated thymidine incorporated into DNA in comparison with Feulgen staining. (o). The larva was injected with tritiated thymidine 24 hours before being killed. The close correlation between bands of DNA which stain intensely with Feulgen reagent. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Sager, Ruth; Ryan, Francis J. (Francis Joseph), 1916-. New York, Wiley
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