Abstract: This work was carried out in the period from 1959 to 1963. Most of the results reported were obtained with Lilium davidii var. willmottiae (Wilson) Roffill. A detailed investigation was made on the appearances of the stages of chromatin extrusion in pollen mother cells, on the relation between bud length, stage of meiosis and chromatin extrusion, and on the effects of mechanical injury and fixing fluids on chromatin extrusions. Results were summarized as follows: 1. Chromatin extrusion or the transfer of nuclear substance from one cell to an adjacent cell is clearly and most frequently observed at the stage of synizesis. The extruding bodies can be regarded as a process of continuous movement in accordance with the stages of nuclear divisions. 2. In Lilium davidii var. Willmottiae (Wilson) Roffill., the development of the anthers within a bud is not exactly synchronous as in Lilium longiflorum, so that there is not always a close relation between bud length, stage of meiosis and chromatin extrusion. As the extrusion phenomena of the nuclear substance depend on the developmental gradient in different anthers within a bud, therefore, the percentage of chromatin extrusion is not always the same in different anthers. By the analysis of variance it is shown that the difference between the buds is highly significant, but not within a bud (see Table 4, 5, 6). 3. By counting the number of cells (each locule of an anther contains about 1000–2000 cells) of Feulgen stained sections of cut and uncut anthers of an entire bud, there is indication that mechanical injury may produce an increase in the extrusion frequency (Table 2, 9). But it is not the chief cause in producing the extrusion of nuclear material. 4. Extruding bodies are present after fixation with formaldehyde, Newcomer's, Carnoy's, Navaschin's, or Flemming's fluid, but there is no significant effect on the extrusion in intact anthers (table 11). Due to the shrinkage in the final preparation of material in these fixatives, it may be a cause in decreasing the decrease in the frequency of extrusion. Morever, there is indication that no relation between the fixing fluids and the direction of extrusion exists. We, therefore, consider that this extrusion phenomenon is not to be attributed to the artifact produced in the fixation. 5. From above evidences we may conclude that the chief cause in producing the extrusion is due to the change in the physiological state of the pollen mother cells.