Duration of the Nuclear Cycle in Tradescantia Root Tips at Three Temperatures as Measured With H 3 ‐thymidine

The duration of the subdivisions of the nuclear cycle in cells from the root tips of Tradescantia paludosa was determined by the labelled mitosis method. These times were found not to increase or decrease in direct proportion to each other at the three temperatures tested, 13, 21 and 30 C. The main difference between the nuclear cycles at 30 and 21 C was in the shortening of the pre‐DNA synthetic period (G 1 ) at the higher temperature. A comparison between the nuclear cycle at 21 and 13 C showed that at the lower temperature mitosis and the post‐DNA synthetic period (G 2 ) were approximately tripled in duration while DNA synthesis was doubled. Cell synchronization and radiosensitivity are discussed in relation to these findings.