ON INFLUENCES OF POPULATION DENSITY OF PLANTAGO VIRGINICA ON ITS MORPHOLOGICAL CHARACTERS STUDIES ON THE REPRODUCTION AND PHOTOSYNTHETIC ECOPHYSIOLOGY OF THE EXOTIC INVASIVE PLANT, PLANTAGO VIRGINICA Influences of Population Density of Plantago virginica on Its Morphological Characters of Underground and Aboveground Organs ON INTENSIVE DISTRIBUTIVE PATTERN OF PLANTAGO VIRGINICA POPULTIONS Comparison of Growth and Chlorophyll Fluorescence Characteristics Between Plantago virginica and P.asiatica under Aluminum Stress BIOLOGICAL AND ECOLOGICAL CHARACTERISTICS OF PLANTAGO VIRGINICA L. Effects of aluminum stress on growth characteristics and biomass allocation of Plantago virginica