What is a bitter principle found in the bark of the privet (Ligustrum vulgare), and extracted as a white crystalline substance with a warm, bitter taste; -- called also ligustron called?

ligustrin — A bitter principle found in the bark of the privet (Ligustrum vulgare), and extracted as a white crystalline substance with a warm, bitter taste; -- called also ligustron. (Webster's 1913.)