I. The influence of NO_3-N and NH_4-N on the growth of Sugi seedlings. One year old seedlings of Sugi (Cryptomeria japonica D. Dox). were grown in a complete nutrient solution including the following three different sources of nitrogen for 184 days, the solution being adjusted to pH 6.2 and pH 4.2. Solution (A): approximately equal proportions of NO_3-N and NH_4-N as source of nitrogen. Solution (B): only NO3-N as source of nitrogen. Solution (C): only NH4-N as source of nitrogen. The following results were obtained. (1) The seedlings made better growth in solution (A) than (B) and (C). (2) The seedlings made better growth at pH 4.2 than at pH 6.2 in solution (B). On the contrary, in solution (C), the seedlings made better growth at pH 6.2 than at pH 4.2. (3) Knop's solution modified by the writers seems to be suitable for the culture of one year old seedlings of Sugi. II. The stimulating effect of artificial aeration of the culture solution on the growth of Akamatsu seedlings. The one year old seedlings of Akamatsu (Pinus densiflora S. et Z.) were cultured in aerated and non-aerated nutrient solution for 194 days, each solution including two different sources of nitrogen....NO_3-N and NH4-N. As the results of the experiment the following results were obtained. (1) The seedlings made better growth aerated solution than non-aerated solution. (2) The effect of aeration in NH_3-N solution is more distinct than in NO_3-N solution.