Cytological examinations of mycelia of strains 59b and 59c were made in order to determine whether the nuclei in the mycelia of strains 59b and 59c differ in number and size. Cultures of strain 59c, which form large, massive fruiting bodies, degenerate easily into the low-yielding puffball-like ancestral form 59b when the mycelium is propagated by transfer. 2. Strain 59c has been propagated by several methods (tissue cultures, cultures of pieces of hyphae, and direct transfer of mycelia). For the 59c-type propagation culture "SS 585, 1.V." was used a culture of pieces of hyphae. New tissue cultures and the mycelium of a monospore culture which forms normal, white fruiting bodies, were examined also. 3. The nuclei were stained by a slightly modified "HCL-Giemsa" method. 4. Strain 59c showed a statistically significant increase in the number of nuclei when compared to strain 59b. The latter strain showed the least variation as regards numbers of nuclei. 5. Strain 59c furthermore showed a statistically significant increase in the size of nuclei when compared to strain 59b. Whereas most of the nuclei of strain 59c measured from 1.72-7.82, almost all of the nuclei of strain 59b fell within the 0.15-3.93 size range. 6. The mycelium of new tissue cultures of fruiting bodies of type 59c was examined after different treatments. In hyphal cultures we try to obtain cells without nuclei of strain 59b, the influence of the environment on the number of nuclei is therefore of interest. 7. The number of nuclei increased with increasing temperature. The mycelia grown at 28 °C and at 24 °C had a statistically significant higher number of nuclei than the mycelia grown at 20 °C. No statistically significant differences were found between the 24 °C and the 28 °C cultures. 8. Mycelia grown on wheat-agar showed a statistically significant decrease in the number of nuclei when compared with mycelia grown on compost-agar.
