Seeds of Crepis capillaris L.(Wall) were worked by means of two methods: 1) exposed to X-rays in doses 2000, 3000, 4000 P or 2) the alkylating agent phosphemid having two groups of ethyleneimine and a pyrimidine bases. In early seedlings we analyzed aberrations of chromosomes in metaphases and of mitotic activity of cells. The seeds were germinated for 24, 27, 31, 36 h. Seedlings of 1-2 mm in length were fixed through 2-12 h after their appearance. Aberrations chromosomes in metaphase plates and mitotic activity of cells were analyzed. Phosphemid induced structural chromosome aberrations of chromatid type. Frequency aberrations on one cell do not exceed the frequency of cells with aberrations using a moderate dose phosphemid. This experiment revealed that in the seedlings of the first arising – 24 h after the beginning of the soaking of seeds frequency aberrations of chromosomes increases as far as their fixing from 3 to 12 h. In seedlings from 27-hourfrequency of chromosome aberrations was slightly higher, than maximal frequency of aberrations is in 24-hour arising (in 12 h after arising). In seedlings, which were selected through 36 h after soaking, number of aberrations of chromosomes with increasing time of fixation increased. Our data allow to conclude that the phase of G1 of dry seeds is heterogeneous relatively mitotical cycle and that a mutagene is saved in cells, in spite of the fact that seeds were washed with running water. Phosphemid suppressed mitotic activity of seedling cells.