Sylvia Boorstein, Ph.D. (2007). “Pay Attention, for Goodness' Sake: Practicing the Perfections of the Heart--The Buddhist Path of Kindness”, p.69, Ballantine Books
Robert Fortune (1847). “Three Years' Wanderings in the Northern Provinces of China: Including a Visit to the Tea, Silk, and Cotton Countries; with an Account of the Agriculture and Horticulture of the Chinese, New Plants, Etc”, p.143