at 25 cm above ground were estimated to be from 35 to 140 R, with a gamma exposure about 21 percent of the total dose. "Nonirradiated" material was taken south of the exclosure gate on the assumption, since reconsidered, that In any event, that area does not now have radiathe area was not irradiated. tion reading above what is considered normal background at NTS. This matter will be given further discussion subsequently. At other places on NTS, there were a few annual species (compared to more favorable years) which germinated and reached the flowering stage. Such was the case at Rock Valley, NTS, where UCLA has had a long-term environmental radiation experiment using a large 137cg source (Kaaz et aZ., 1971; French et al., 1974). Doses were known for all parts of the irradiated area, which allows an estimate of total doses to both annuals and shrubs. Moreover, these doses are within the range of vegetation in the Pu-contaminated areas. For this reason, we collected annual species from the Rock Valley area to develop the technology for both collecting and examining annuals. Ten species were collected, of which only one, Phacelia fremontii, contained cells at the proper developmental stage for examination. Phacelta fremontit has N equal 13. Flower buds of both shrubs and annuals were collected and kept in an ethyl alcohol-acetic acid fixitive for 24 hours, then transferred to 70 percent ethyl alcohol in which they were returned to the laboratory for examination. In the laboratory, all collections were examined by the Beeks method (Beeks, 1955), which requires that anthers are squashed in acetocarmine and Hoyer's medium on a microscope slide. Slides were examined and photographs taken of both normal cells and those which provided possible evidence of abnormality for both irradiated and nonirradiated areas. Detection of radiation damage to chromosomes depends, in visual methods, on observing particular chromosome configurations at or near Metaphase I, for certain conditions which are not considered normal. Among these are (1) any synaptic configuration larger than a bivalent pair, that is a trivalent or quadrivalent configuration which may appear as a ring or chain, (2) lagging bivalent chromosomes when other chromosomes have already moved to the poles, and (3) incomplete pairing among otherwise paired bivalents. Another condition is the production of dicentric chromosomes which produce "bridges" between nuclei and chromosomal fragments, but these have not been observed so far. There are still other conditions. Chromosome "stickiness" may result from radiation damage, but may also be an artifact of preparation methods. Other preparation artifacts may also appear essentially the same as radiation effects. Conditions which were observed will be described more fully in the succeeding paragraphs. Figure 1 shows two nuclei of cells of Artemista spinescens at Metaphase I. Nine bivalent chromosomes are clearly visible, consisting of four bivalent rings, that is chromosomes having two chiasmata near the ends of each bivalent pair, and five other bivalents, with only one chiasma on each bivalent pair. These are considered typical normal cells and were chosen because of the ease with which individual chromosomes can be distinguished. It should be pointed out perhaps that analysis of chromosome conditions are not possible solely on the basis of photographs and that much additional information can be gained 113