1. Mean amount of apparent photosynthesis of tulip(cv. Apeldoorn) in every 5 days from May 28 to April 30 was shown to be almost consistent ranging from 800 to 900 mg/m^2/hr, except under the extreamly low radiation due to rainy weather. Then after the mean amount became lower gradually but it was kept to about 50% of the maximum amount until withering period.
2. Apparent photosynthesis increased with sun rise keeping high level until noon, then declined.
3. Upperleaves were more active in apparent photosynthesis than lower leaves. The wind up to 9m/sec. promoted apparent photosynthesis on the fine day.
4. The spacing hardly affect on apparent photosynthesis until the plant number per are increased to 6,000 and the close spacing resulted in the lower apparent photosynthesis.