g a third dimension by focusing directly from the microscope which allows viewin vertically on the slide preparation. the left has a ring of Figure 2 shows cells considered abnormal. The cell on The cell on the right. lower four chromosomes forming a figure "8" on the a chain of four right has both a ring of four chromosomes (upper left) and chromosomes (upper right). red abnormalities. Figure 3 shows still two other cells with what are conside ts which appear bivalen The cell on the left is in Metaphase I and has eight The cell paired. y properl normal and two univalents which do not appear to be on the right is in Telophase I. The bivalent chromosomes in the center belong normally to the group of chromosomes on the left and do not appear to be moving to that pole. In the subsequent nucleus which is to be formed, this bivalent omes pair would probably be omitted and the genetic components of those chromos would be lost to that cell which normally divides again meiotically to form pollen grains. DISCUSSION In addition to detection of possible abnormalities by visual examination of the chromosomes themselves, an attempt was made to determine whether there might be a change in pollen production between irradiated and nonirradiated areas. Pollen grains per anther were counted, but their very large numbers coupled with changes in anthers attributable to insect damage or pathological conditions due to unknown factors caused this approach to be abandoned. It should be noted in passing that the germinability of pollen grains in artificial media serves in other botanical investigations and may be also applicable to the objectives of this work. Beatley (unpublished) has looked at the germina- bility of the pollen of Larrea tridentata around the Sedan event. The possibility of artifacts resulting from chromosomal preparations is difficult to assess for several of the abnormal conditions noted. For others, notably the occurrence of quadrivalent or hexavalent rings, there is little likelihood of preparational artifacts. These conditions have been shown to result from breakage with exchange of segments among nonhomologous chromosomes, conditions remote to those attributable to preparational artifacts. The frequency of occurrence of abnormalities among irradiated and nonirradiated populations offers hope in resolving this problem. The abnormalities observed here occurred in both irradiated and nonirradiated populations, but there appears to be more occurring in the irradiated population. Of the 12 total aberrant cells noted, six occurred among 119 cells which were examined from the irradiated population. Six others occurred among 360 cells examined from nonirradiated shrubs. It is apparent that abnormalities are infrequent. On this basis, 5 percent of the irradiated population of cells appeared abnormal, and 1.7 percent of the nonirradiated cells appeared abnormal. Because of the nature of cytological investigations, these numbers are probably not adequate 115