Charles Sanders Peirce, Nathan Houser, Christian J.W. J. W. Kloesel (1992). “The Essential Peirce, Volume 1: Selected Philosophical Writings? (1867–1893)”, p.149, Indiana University Press
Erasmus Darwin (1807). “The Botanic Garden: A Poem, in Two Parts: Part I. Containing The Economy of Vegetation. Part II. The Loves of the Plants”, p.117
Swami Vivekananda, Swami Adiswarananda (2006). “Vivekananda, World Teacher: His Teachings on the Spiritual Unity of Humankind”, p.24, SkyLight Paths Publishing