1. Shreve, F., Plant World 13: 235 (1910).
2. Turner R. M. unpublished data.
3. Alcorn, S. M., Cactus and Succulent J. 31: 39 (1959).
4. Beatty L. D. thesis University of Arizona (1955).
5. Natural History of the Long-Nosed Bat (Leptonycteris nivalis Saussure)