Abstract
The effect of gamma rays from cobalt-60 on cuttings of seven chrysanthemum varieties has been studied. The LD 50s for the cuttings were in the range 3·0–4·3 krad. Irradiation caused plants to flower much later than controls. About 40 per cent of the irradiated plants showed colour sports; the overall percentage of sports and the percentages of different types depended markedly on variety. One sport of one variety appeared to be caused by the breaking of a periclinal chimaera. The remainder were believed to be mutants in the broadest sense of the term. The number of mutant cells was estimated to lie between 2·2 and 27 per 10 6 cells per krad. Most sports were produced by irradiating varieties with a chromosome number of 54 and fewest from those with the highest chromosome numbers. A hypothesis is advanced that radiation-induced sports may have more chromosomes than their parent, but rarely have less.
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