On the Influence of Ultra-violet Rays upon the Frequency of Nuclear Division in Plants

Abstract

1. When root-tips of Vicia Faba, L. are exposed to the ultraviolet rays from a quartz mercury lamp the number of nuclear divisions is greater an the side of the ray source than an the opposite side during the first few hours after exposure, the number progressively increasing to the maximum. After reaching it at the end of the second or third hour after exposure, the number begins to decrease below the normal frequency.2. A tendency to recover the normal frequency of nuclear divisions becomes recognizable after an elapse of time (a day or two days), if the material has not been exposed for too long.3. When an exposure is made of considerable length, no indication of recovery is observed, so far as the present investigations are concerned.4. When the material is exposed to the rays of 2535-2537Å, no increase in the number of nuclear divisions is found, but a decrease takes place which is already conspicuous immediately after exposure, although a tendency to recover the normal frequency is recognizable after an elapse of time.5. When the material is exposed to the ray of 3655Å for 3 hours, the frequency of nuclear division is above normal for a time, followed by a decrease below normal. This presents a marked contrast to the Gase of irradiation for the same length of time by the rays of 2535-2537Å in which the frequency is lower than normal from the first moment after exposure.