Seeds of the third inbred generation of the very fruitful variety, First Early, were exposed to X-rays. Eighty-one seeds previously kept on moist filter paper at 27 deg. C. received a dose of about 10,000 r. at 300 r. per minute. Fifty plants from treated seeds were transplanted to the field of which 46 reached maturity. Thirt-six were normal in fruitfulness and 5 were distinctly less fruitful and 5 had only 5 fruits or less. One plant was a chimera having a component with abnormally narrow leaves. Seed was planted from several R1 plants including 52.162.7. This plant was unhealthy but recovered. Its pollen varied in amount but when examined in I-KI solution contained about 75 per cent normal-looking grains and seed production was about normal. R2, obtained by selfing, contained 8 seedlings which were very fruitful including one 52.112.13 that seemed unusually early ripening, and 3 similar mutants determinate in growth. One of the mutants produced no fruit, another produced a few small fruits very late in the season and the third died of curly top. No difference from the normal in leaf or flower was observed.
The R3 generation from the early fruitful plant 52.112.13 selfed contained 59 normal, 24 mutants and 7 undetermined. This mutant (w\2\) was different from the determinate mutant that occurred in R2 and closely resembled the "wiry" mutant described by Lesley and Lesley (Jour. Hered. 19, 1928) and by Schiemann (Z.I.A.V. 63, 1933). The ovary, however, seemed more often syncarpous. The mutation presumably was caused by the X-rays but if so, why did not the mutant appear in the inmediate progeny of the X-rayed seed? Apparently the mutation occurred in 2 stages. An ingenious explanation, supplied by Dr. T. M. Little, University of California, Riverside, is that the mutation to w\2\ occurred only in some cells of the treated seed which developed into the R1 plant 52.162.7. Thus, it was a chimera and either the eggs or the pollen were derived from mutated cells, not both. Hence, its progeny, R2 family 52.112, were either heterozygous for the mutation or did not contain it. A heterozygous R2 plant 52.112.13 selfed gave in R3 a mono-hybrid ratio for the recessive mutation resembling wiry.
The possible relation of the R3 mutant to the determinate mutant that occurred in R2 should be studied.