In the genus Cycas, the sex chromosomes have been reported in Cycas pectinata by Abraham and Mathew (1962) . According to their studies, the sex chromosomes of this species belong to the X-Y type, and the only difference between the X and Y is that the X bears a satellite at the end of one of the arms, while the Y does not. In Cycas revoluta the sex chromosomes have not yet been definitely reported, though cytological studies have been made by several investigators (Ishikawa 1916 , Kuwada 1929

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... akamura 1929; Sax and Beal 1934) . In this paper the karyotype of the female and male plants will be treated, with special reference to the sex chromosomes. MATERIALS AND METHODS Materials were collected from the female and male plants of Cycas revoluta Thunb. growing on the campus of Hiroshima University. The root tips were pretreated in 0.004mol/l aqueous solution of 8-hydroxyquinoline for 5 hours and fixed in 45 % acetic acid for 20 minutes. The fixed materials were macerated in 1:1 mixture of 45 % acetic acid and 1N-HC1 at 60°C for 20 seconds and stained with 1.5 % aceto-orcein. For karyotype analysis, individual chromosomes were measured and arranged in descending order of size. For the convenience of comparing the chromosome size with each other, the relative length method was used; namely, the ratio in percent of the length of an individual chromosome to the total length of the whole chromosomes in the complement was calculated. The chromosome shape, determinable by the position of the primary constriction, was recorded as either V or J, according to the F % values (the fractional ratio in percent of the short arm length to the total length of the chromosome) fell within a range of 50-41 or 40-20, respectively. RESULTS