AbstractA series of experiments was performed designed to determine the relationship between hull covering and seed and germ size to X-ray sensitivity of oat seed of three varieties: Mo. 0-205, Simcoe, and Bonham. The seed contained approximately 14 and 20 percent of moisture and X-ray dosages of 40,000 and 30,000 r were used. The data indicated that: 1. Hull-coverings may or may not afford protection to the seed from X-rays. Both varieties and moisture content produced differential reactions. 2. Large seed were more affected by high X-ray dosages than were small ones. Larger seed have larger germs, exposing more area to X-ray effects. A decrease of germination and seedling vigor was obtained when large seed were exposed to radiation, although there was no indication of a proportional decrease between germ size and relative damage to seedlings from large and small seed. 3. Germination percentages of oat-seed lots receiving up to 40,000 r of X-rays were as good as those of the checks, when measured on blotters in a plant germinator, but seedling vigor was materially reduced. Lowered germination percentages noted in greenhouse experiments were probably due to insufficient vigor to grow through the soil on the part of many seedlings. Probably all of the X-ray effects at the dosages used were caused by decreases in seedling vigor. 4. Radicals and plumules of the seed were equally damaged by X-ray treatment.
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