Apical growing regions of two varieties of Z. linearis, Orange and White, were treated with 0.2% colchicine for 12 hours (four hours daily for three days). Survival of plants till maturity was less in colchicine treated ones than in the controls. Typical effects of colchicine like slow growth of plants during early stages of development, thicker, leathery and deformed leaves, shorter internode, increased basal circumference and more number of branches were observed in the treated plants in comparison with the control. In addition to this, colchicine treated ones of both the varieties had less number and bigger sizes of stomata in comparison with the control. In the colchicine treated plants of the var. White all the buds dried up before the flowers opend while the control plants flowered and had seed formation. Significant increase in pollen size and sterility was observed in the colchicine treated plants of the var. Orange in comparison with the control. Meiotic count of n = 12 chromosomes was made from some of the control and colchicine treated plants in the var. Orange while n = 24 chromosomes was counted in a few of the colchicine treated ones. Meiotic irregularities like unequal separation of chromosomes at anaphase I were noted in some of the treated ones while control plants were free from these. Irregularities during pollen grain formation were also noted in the colchicine treated ones. Number of fruit (seed) per capitulum was significantly higher in the control plants. © 1969, Japan Mendel Society, International Society of Cytology. All rights reserved.