Cell chamber structure and influences factors analysis on sugarcane stem tips browning in vitro TECHNIQUES FOR VIRUS-FREE SWEET POTATO CULTURE STUDIES ON HISTOLOGY AND PHYSIOLOGY OF THE ORGANGENESIS AND SOMATIC EMBRYOGENESIS OF POPULUS ALBA× (P.DAVIDIANA×P.SIMONIIP.TOMENTOSA IN VITRO Study on Stem-tip Tissue Culture of the Traditional Chinese Medicine Chrysanthemum morifolium Regeneration System Establishment of Disease-resistant Asparagus Variety In Vitro Tip Micropropagation of Ligularia jamesii from Changbai Mountain Cell division frequency difference in various regions of stem tip protomeristem in sugarcane varieties with different stem diameters ELIMINATION OF MLOS FROM PAULOWNIA TISSUE CULTURE BY MEANS OF THERMOTHERAPY COMBINED WITH STEP TIP CULTURE