This report deals with the experiments on the cause of the low rooting ability of cuttings of Pinus Thunbergii.
1. The ether and water extracts were obtained from the shoots of P. Thunbergii in January. Those extracts inhibited rooting of the cuttings of Populus sp, and Amorpha fruticosa.
2. The growth inhibitors were found, but no growth stimulators were found in acid and neutral fractions of above ether extracts.
3. The rooting ability of cuttings tends to decrease with increasing mother tree age.
4. The growth inhibitors in cuttings tend to increase with increasing tree age, especially remarkable in acid fraction. The growth promotors in acid fraction tend to decrease with increasing tree age. (These experiments were done in June.)
5. The amount of the growth inhibitors of acid fraction in Pinus Thunbergii and Pinus densiftora cuttings which have low rooting ability are greater than that in Cryptomeria japonica, Metasequoia glyptostroboides and Sequoia sempervirens cuttings which have high rooting ability.
From these results, it may be considered that rooting inhibitors exist in the cuttings of Pinus Thunbergii, and those substances are related to the growth inhibitors.