The Effect of X-radiation on the Meiotic and Mitotic Divisions of Certain Plants

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Abstract
The effects upon meiosis in Tulipa silvestris and Rhoeo discolor, and on mitosis in Crocus olivieri are described. The treatment has no immediate visible effect upon either division. Applied 1-3 mos. before meiosis, it does not seriously affect meiotic behavior, though occasional fragments are seen at late stages; but when applied 24 hrs. previously it induces destructive changes at meiosis which first become apparent at anaphase. Mitosis, following treatment, is brought rapidly to a standstill for a period, after which abnormal divisions occur involving simple fragmentation and translocation. It is suggested that a physiological reaction is induced which becomes more, and then less, intense, and which prevents cells about to divide from entering mitosis but allows those already in mitosis to complete division, owing to the rapidity of the process. The cells are therefore submitted to the most intense period of the reaction during an enforced resting stage. The abnormalities are initiated at this stage. The effect of this reaction upon chromosomes at meiosis alters them, so that if they are subjected to the stresses at anaphase during their temporarily altered condition, abnormality involving destruction results. The simpler changes involving fragmentation are induced in those cells which do not reach anaphase in their altered condition. The essential difference between the induced abnormality at meiosis and mitosis is therefore due to the difference in time taken by the division to reach completion.

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