The Fine Structure of the Nucleolus Organizers of Lilium longiflorum During Meiosis

Nucleolus organizers in meiotic prophase of Lilium longiflorum microsporocytes were studied with the electron microscope and found to be less electron-dense than the majority of the chromatin and the nucleolus. The structural units of the nucleolus organizers were observed to be loosely arranged fibrils, 75-125 A in diameter. This organization was interpreted as an intermediate stage in chromatin condensation, indicating decreasing synthetic activity, as was suggested by previous workers on mitotic nucleolus organizers.