The research of extreme low (10°С) and high (37°С) temperatures influence under in vitro conditions on phenotypic display of three mutations in Nicotiana tabacum L. with of a certain morphological type domination was conducted. The BG-141.4 line is character- ized by low-cellular embryo sacs formation, in the SG-27/4 line the trait of the increased number of nucleus and cells in embryo sacs exhibits, the line М-3 differs by high frequency of cenocyte low- cellular embryo sacs. In the mutants at ovary cultivation in a normal temperature conditions (25°С) the process of embryo sacs forma- tion was realized by its typical mode and replicated a phenotype described for plants of mutant lines, grown on the experimental field under in vivo conditions. Temperature conditions substantially modified a gametophyte mutations display, thus extremely low or extremely high temperature on embryo sacs development had distinctly expressed specificity. In three mutant lines and in control non mutant line BG-6 a low temperature in the gametogenesis depressed a mitotic divisions and cytokinesis. As a result over all lines at this temperature mode the cenocyte low-cellular embryo sacs dominated. Action of a high temperature in a gametogenesis mainly induced additional mitoses. Such effect is most distinctly observed in control and in mutant with the increased number of cells in embryo sacs, however at both low-nuclei mutants at 37°С the tendency to multinuclear embryo sacs formation also is traced. Obtained data show, that quantitative expressiveness of embryo sacs modifications under the temperature conditions substantially depends on a genotype.