Tlhis paper treats of the differences in the shade tolerance between P. densiflora and P. Thunbergii, and is a part of the writer's research on their habitat segregation.
It was made during the period 1965 and 1967.
One-year seedlings were planted in each plot at the end of March, 1965, and each plot was shaded with white saran screens at the begining of May.
The quantity of sunlight in each plot was varied with the number of saran screens, and the relative light intensity was shown in Table 1.
The results obtained are as follows :
1)The number of dead seedlings increases as the light intensity decreases. In the case of P. densiflora it is larger than in the case of P. Thunbergii.
2)The diameter and the height decreases as the light intensity does. (Fig.2 and Fig.3) In plot below 40% sunlight, the length of stem which extends in the second year decreases excesslvely. (Fig.4)
3)Shading strongly influences the dry weight of the top. The weight in a plot of 40% sunlight is lower than half of that in the normal sunlight. (Flg.6)
4)Shading also influences the dry weight of the leaves, which decreases remarkably as the light intensity does. (Fig.7)
In the above (2), (3) and (4), there is little defference between both species.
From these results, it may be said that P. densiflora is about the same as P. Thunbergii in regards their shade tolerance.