Pandiangan, Dingse. 2011. “Perubahan Morfologi Dan Anatomi Kalus Catharanthus Roseus Dengan Perlakuan Triptofan (The Morphological and Anatomical Changes on Tryptophan-Treated Callus of Catharanthus Roseus)”. JURNAL BIOS LOGOS 2 (1). https://doi.org/10.35799/jbl.2.1.2012.379.