Comparison of Responses of Larix principis rupprechtii and Picea meyeri Seedling Growth to Light Availability and Planting Density under Controlled Environment Effects of GA3 on the Survival Rate and the Net Photosynthetic Rates ofMicropropagation Plants of Phlox paniculata Transplanted during Winter in Beijing Area Effects of GA3 on the Survival Rate and the Net Photosynthetic Rates ofMicropropagation Plants of Phlox paniculata Transplanted during Winter in Beijing Area