THE BIOLOGICAL EFFECTS OF X-RAYS ON MATING TYPES AND CONJUGATION OF PARAMECIUM BURSARIA

1. Individuals of opposite mating type of Paramecium bursaria were irradiated with roentgen rays at dosages ranging from 100,000 r to 1,000,000 r in steps of 100,000 r. 2. After 100,000 r, locomotion of the paramecia became markedly accelerated but with higher dosages locomotion was retarded. None was able to survive dosages of 700,000 r or more. 3. Clones of P. bursaria have been established in the laboratory from specimens irradiated with 300,000 r-600,000 r. One result of such irradiation is the destruction of the contained green symbiotic zoöchlorellae living with in the paramecia. A method is now available for the production of colorless clones of P. bursaria. 4. Colorless P. bursaria as produced by irradiation have the same sex type as before irradiation. Such specimens readily mate and conjugate with members of the opposite sex type. 5. Members of one mating type are more susceptible to x-rays than those of opposite mating type. This may in reality be only a racial, not a sexual difference. 6. Paramecia of opposite sex types will, when irradiated and mixed, enter into the mating reaction. Clumps thus formed are smaller than in controls and the time taken to form them is greater. The lag in time between conjugation and the mating reaction is dependent upon the dosage. 7. Irradiated conjugants remain joined together in the sexual process much longer than those of the controls. 8. Irradiation inhibits division but the effect is only temporary. After a period of time (depending upon the dosage) survivors have a division rate similar to control specimens. 9. Irradiated culture fluid has no toxic or lethal effect upon unirradiated specimens of P. bursaria. 10. Irradiation-killed specimens of one sex type do not mate or conjugate with living, unirradiated members of the opposite sex type nor does it result in selfing.

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