RETROSPECT AND PROSPECT ON PLANT INTRODUCTION AND ACCLIMATIZATION IN SHAANXI PROVINCE STUDY ON INTRODUCTION AND ACCLIMATIZATION OF FINE HERBAGEIN THE LOESS HILLY REGION Introduction and acclimatization of Camellia tunghiensis a rare and endangered plant PEST PROBLEMS AND ITS MANAGEMENT STRATEGIES OF PLANT INTRODUCTION AND ACCLIMATIZATION Fifty Years of Botanical Gardens in China