The clone seedlings of Cryptomeria japonica naturally regenerating in Mt. Sanbe were planted in 0.4 m x 0.4 m spacing in the nursery of Shimane University, dividing into mono-planting plot and mixed-planting plot in March, 1977. The height and basal diameter of seedlings were measured in each autumn from 1977 to 1981.
1. Differences in each character (D_0, H, D^2_0･H, H/D_0) of seedings were recognized among the clones in mono-planting and mixed-planting plots and in each aged seedlings.
2. In mixed-planting plot where the value of the characters were generally small, there were some clones that grew faster than those in mono-planting plot, particularly for D_0 and D^2_0･H.
3. The broad sense heritability of each character was greater in monoplanting plot than that in mixed planting plot. The heritability of each character changed by age of seedlings, smallest in two years and greater in more than three years. The maximum of height (60%) appeared in 4 years seedling, of D_0 (38%) and D^2_0.H (45%) in 5 years and H/D_0 (85%) in 3 years, respectively.
4. The maximum of genetic gain of each character were following : H : 24 cm in 4 years of mono-planting plot, D_0 : 2.5 mm in 5 years of mixed planting plot and D^2_0･H:491 <cm>^^^3 in 4 years, respectively.