Radiosensitivity of self- and cross- pollinated seeds, and of seeds with a marker gene in Sugi, Cryptomeria japonica D. Don was studied. Five seed groups, namely, selfed seed lots of naturally (TG-5) or gibberellin induced flowers (BG-5) of a tree, G-5, and naturally set flowers (C-5) of another tree, C-5, and TG-5×C-5, and open pollinated seeds of TG-5, were irradiated with acute gamma rays (3, 000 R/day) of 6, 000, 12, 000 and 15, 000 R in the gamma field of the Institute of Radiation Breeding. The selfed seeds from gibberellin induced flowers had less viability in the control and after gamma ray treatment they showed further retardation in germinability. On the other hand, open pollinated seeds from TG-5 showed the highest resistance to the radiation. Hybrid seeds between two trees showed intermediate germination percentage between those of open pollinated seeds and selfed seeds of artificially induced flowers, and a slightly higher value than those of selfed seeds of both of their parents, indicating a heterotic effect of the hybrid seeds on the radiosensitivity. With those germination percentage resulted from the irradiated seeds, genetical and physiological share on the radiosensitivity was estimated, and the genetical portion was dominant over the physiological in 12, 000 and 15, 000 R exposure.
The tree, G-5, proved to have a recessive gene producing seedlings with light green cotyledon in 3:1 ratio after selfing in both naturally or gibberellin induced flowers. The selfed seeds (BG-5) after gibberellin treatment were irradiated with gamma rays to examine their segregation ratio, and biased ratios favouring lower percentage of the variants were noted. It was thought that the genetical composition of a seed population may be slightly changed in the X₁ population by selective damage of the radiation on seeds with some special genotypes.
Abnormality in cell division expressed by percentage of cells with chromosomal bridge increased linearly with the intensity of gamma exposure.

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Needless to say that a complete forest road system is the basic facility which enables the modern rationalized management of forest industry. According to the official statistical report for 1962, the average density of forest road in Japan which is available for truck hauling, is only a little more than 2 meters per hectare of the economic forest area. This figure is obviously too small when compared with that of European countries.
Urgent need in the Japanese forestry is the further construction of more forest roads. Therefore the problem finding the most adequate forest road density to fulfill the demand of modern mechanized logging operations and intensified forestry management has recently come to be taken up as the focus of discussion.
The author tried to find out a theoretical approach to solve the problems from the view point of logging economy. In this paper, some results of such investigations are reported.

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Previously the author estimated by grafting experiment that the witches broom of Pinus densiflora is not parasitic but hereditary. In the present paper, it is reported that seeds collected on the grafted witches' broom segregated into 19 normal seedlings, 10 witches' broom plants and one extraordinarily small but not witches' broom plant. This ratio of segregation is not significantly different from 1/2 nor 1/4.

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