A cyclic staining behaviour of the chromosomes during mitosis and meiosis

Abstract

1. 1. After the fixation of roots and anthers in Lewitsky's fluid the chromosomes in mitosis and meiosis show a cyclic staining behaviour in a mixture of orange G and aniline blue. In mitosis the change occurs before the dissolution of the nucleoli and in meiosis when the dissolution of the nucleoli is almost complete. 2. 2. In root tips of seven species the euchromatic parts of chromosomes stain yellow from about mid-prophase to the end of anaphase but blue at telophase, interphase and early prophase. Heterochromatic regions, however, in species where they are detectable, stain yellow at all times except in early prophase. 3. 3. A deviation from this staining behaviour is found in root tips in a narrow region of peripheral cells and in cells adjacent to the root cap. In these cells the chromosomes at all times stain yellow and the cytoplasm yellowish. A study of the early development of lateral roots in Vicia faba indicates that this is not an artefact. 4. 4. Examination of pollen grains in two diploid species of Tradescantia show that during mitosis the chromosomes undergo changes in staining similar to those found in meristematic cells. The vegetative and generative nuclei which arise from this mitosis have different staining qualities. The vegetative nucleus stains blue for a long period of pollen development but ceases to stain at all just before anthesis; the generative nucleus, however, stains blue for a brief period and yellow thereafter. 5. 5. In pollen-mother cells the chromosomes stain blue at leptotene and pachytene but yellow during diakinesis. At the second division the chromosomes stain as in mitosis. 6. 6. Under these conditions of fixation and staining, nucleoli always stain yellow, the cytoplasm stains greyish, the spindle blue but the nuclear sap remains colourless. The cytoplasm in the “vegetative cell” in pollen grains has an increased tendency to bind orange G. 7. 7. The staining behaviour of the chromosomes and nucleoli are briefly discussed in relation to earlier ideas on the chromosomal “matrix”.