Hamad, M . S ., et al. “Influence of Sucrose and Tyrosine on Callus Induction and Morphine and Codeine Production on Papaver Somniferum In Vitro”. Journal of Biotechnology Research Center (JOBRC), vol. 4, no. 2, June 2010, pp. 45-53, doi:10.24126/jobrc.2010.4.2.120.