Notes on Southwestern Cacti
The writers have spent considerable time during the last few years studying cacti in the field, in the herbarium and in the garden of the senior author. The following are some of the results of this observation. Specimens cited are in the Pomona College Herbarium.
Pierce, Wright M. and Fosberg, F. R.
"Notes on Southwestern Cacti,"
Bulletin of the Southern California Academy of Sciences:
Available at: https://scholar.oxy.edu/scas/vol32/iss3/6