Chlorophyll Fluorescence Characteristics of Elaeagnus angustifolia L. and Grewia biloba G.Don var.parviflora(Bge.)Hand.-Mazz. Seedlings under Drought Stress Physiological Characteristics of Elaeagnus angustifolia and Grewia biloba G. Don var. parviflora Seedlings under Drought Stress TAXONOMIC NOTES ON THE GENUS GREWIA L. IN YUNNAN Ecosystems water use patterns of Quercus variabilis and Grewia biloba based on stable hydrogen and oxygen isotopes in the south aspect of Taihang Mountains