In the practice of silviculture we are often impressed with the necessity of identifing the species of seeds or seedlings just germinated. However Pinus densiflora SIEB. et ZUCC. and P. Thunbergii PARL. are hard to distinguish in their seed stage. It is also much more difficult to distinguish between them by the external form of their seedlings in the year of germination. Therefore the authors have sought for a method of distinguishing the seedlings of P. densiflora from P. Thunbergii during the year of germination by the anatomical characters of their cotyledons and primary leaves. 1. The cross-section of the cotyledon of P. densiflora is always a regular triangle in shape and the apex of the ventral side is acute, but that of P. Thunbergii is always an isosceles triangle in shape, based on the dorsal side, and the ratio of the length of the base to the other side is 1:1.2 ; Moreover the apex of the ventral side is much more obtuse than that of P. densiflora. 2. The endoderm of the cotyledon of P. densiflora is always circular in shape, but that of P. Thunbergii is usually elliptic in shape, the long axis being dorsiventral. 3. In the primary leaves of P. densiflora, the sclerenchyma cell surrounding the resin canal is always absent at the part touching the epiderm and 2 to 4 of the secreting cells are close to the epiderm. on the other hand, in the primary leaves of P. Thunbergii, the sclerenchyma cells are usually continuous and surround all the circumference of the resin canal, but the resin canals are close to the epiderm. Rarely a sclerenchyma cell is absent at the point touching the epiderm and one of secreting cell is close to the epiderm. Then it becomes clear that the resin canals of the primary leaves of P. Thunbergii lie somewhat inward comparing those of P. densiflora. And it is true of the adult leaves. In the adult leaves the resin canals of P. densiflora are close to the hypoderm, but those of P. Thunbergii lie in the green tissue and after adult leaves have appeared (which is generally in the Autumn of the year following the Spring germination) it is easy to distinguish between them by the site of the resin canals in the adult leaf. In both spesies, the number of resin canals in adult leaves is generally 2 within about three full years after germination, and 3 to 4 develop within four or five years. Thereafter the resin canals gradually increase in number, usually to 12, very rarely to 15. In seedlings and trees of vigorous growth the resin canals usually extend from the base to the top of the adult leaf, but in cases of poor growth the canals disappear half way up the leaf or ever earlies.