Technical manipulations for increasing the effectiveness of treating rice seedlings with colchicine are descr. Two applns. are made 24 hrs. apart, of either 0.1% or 0.05% aqueous colchicine. After the 2d appln., the soaked cotton plug which was inserted into the growing shoot is removed. Increases in the concn. of colchicine and/or the no. of applns. proved to be detrimental and even fatal to rice seedlings. By these modifications, monocotyledons may be treated quite as successfully as dicotyledons. Proper care of treated seedlings and correct selection of the tetraploid panicles are important.Nine vars., including 10 seedlings from each var., were used. Of the 90 seedlings thus treated, 56 survived and 23 of the surviving individuals contained 4X tissues. Polyploid tissues were obtained from one or more seedlings of each var. tested.