Seasonal variations on the growth and the content of saikosaponin a, c and d (%DW) in the main root of Bupleurum falcatum were investigated using plants monthly collected from July to December in 1993. Bolting started in September, and then the growth of aerial parts and the main root reached the maxima in October. As the maximum diameter of the main root increased rapidly from August to October, a lignified tissue in the xylem of the main root increased remarkably. The content of each saikosaponin (%DW) in the main root was higher in the early time than in the latter time. The total content of saikosaponins (%DW) decreased rapidly from September to October and did not change in December. As regards the distribution of the saikosaponins in each tissue of the main root during cultivation, each saikosaponin accumulated most in the outer tissues from the phloem layer, especially from the pericycle and its neighbouring tissues. The composition of saikosaponins in each tissue in the main root changed significantly during cultivation ; thus in the outer tissues from cambium the content of saikosaponin d (%DW) relatively high. On the other hand in the xylem tissue, the inner tissues from cambium, the composition was quite different from that of the outer tissues as follows : in August and September the content of saikosaponin c was relatively high. After September saikosaponin c was obviously detectable, while saikosaponins a and d were not detectable.
