Abstract: The influences of the population density of Plantago virginica on its morphological parameters were investigated at modular level. The results showed that the correlations between the morphological parameters and the population density in the vegetal period were not obvious, while those in the reproductive period were obvious. In the reproductive period, the relationships of the population density(X) with the leaf number(Y₁)、leaf length(Y₂)、leaf breadth(Y₃)、fresh weight(Y₄)、root weight(Y₅)、spike number(Y₆)、spike length(Y₇)、flower number(Y₈)、spike weight(Y₉) and spike weight/vegetal weight(Y₁₀) followed:Y₁=22.0428-2.3022lnX, Y₂=21.4185+2.1828lnX, Y₃=4.9934-0.5048lnX, Y₄=0.1567+699.574/X, Y₅=7.7310X^-0.7606, Y₆=0.9019+318.886/X, Y₇=2.4236+179.425/X, Y₈=46.3069+6914.07/X, Y₉=0.1382+15.9598/X and Y₁₀=0.047+0.0002X. The density dependences of Plantago virginica and Plantago asiatica were also compared.

Key words: Plantago virginica, density dependence, morphological parameters