whetee Cee ee eae as mete Ratatat nat Me Fig. 7, Small spheres are extranuclear bodies in Machaeranthera torttfolia. Aberrations observed on the two radiation doses include dicentrics and fragments in anaphase I — telophase I! and anaphase If ~— telophase II (Fig. 13). Of the 2,839 cells scored, 1,866 were from seven plants from the enclosure near the radiation source with doses ranging from 3.2 R/day to 4.8 R/day; and 973 were collected from four plants outside the immediate range of the radia- tion source with a dose of less than 1.0 R/day. The anaphase I — telophase I cells with the higher dose had 9.1% aberrations, as compared with 1.0% from the cells from the lower dose area. For anaphase II - telophase II 10.4% of the cells from the higher dose area were aberrant compared to 2.8% of those in the lower dose area (Table 3). 362 Fig. 8. The infrequent condition of five bivalents and two univalents (note arrows) in Machaeranthera torttfolta. The Mann-Whitney test indicated a difference in the average proportions of aberrants between the two populations at the 99% confidence level. (Test statistic = 28; w.005 for a two-tailed test = 27; the nutl hypothesis that the populations are the same could therefore be rejected.) Because of the small number of cells found in metaphase I we have not tabulated these data; however, one plant from the higher dose area showed 94.9% aberrations and one plant from the lower dose area had only 1.6% aberrant cells, The high value for these metaphase I aberrations was primarily due to a large number of cells with four bivalents and one quadrivalent, suggesting that the plant was heterozygous for a translocation (Fig. 14). 363