Labelling of the nuclear cycle with3H-thymidine and the determination of the minimum mitotic cycle by means of colchicine have shown that a 0,4% v/v concentration of ethyl alcohol given to root tips ofAllium cepafor two hours induced a mitotic delay of 13 hrs. The S phase is delayed 6 hrs, and the delay of G, is calculated to be about 7 hrs; G2and prophase are not aifected by the treatment.