Strong seasonal and plant density effects on several plant and crop characteristics were observed (Figure 1 and Table II). Numbers of flowers per plant, plant fresh mass and plant dry mass decreased with plant density, this decrease being larger in summer than in winter (Figure 1). Final plant fresh mass at 48 plants m2 (Figure 1B), was 2.6 times higher in Expt. 4 than in Expt. 6 (for plant dry mass this factor was 3.1) and plant mass in the other experiments was intermediate. The differences in ratio (2.6 versus 3.1) can be explained by variation in the dry-matter content throughout the season: plant dry matter content was about 2.0% higher (13.3% instead of 11.2%) in Expt. 4 than in Expt. 6 (Table II). Stem length showed an optimum response to plant density with a maximum length at 64 plants m±2, however, differences between densities were small (