Support for this study was graciously provided by a grant-inaid for research from the Society of the Sigma Xi. Appreciation is expressed to Our Lady of the Lake College which granted me time for the study and made available certain facilities for growing and photographing the plants. Gratitude is also expressed to many individuals who contributed in various ways to the completion of the present study. First among them is Mrs. Roy W. Quillin (Ellen D. Schulz) who gave constant encouragement and advice and the use of books from her fine library on the Cactaceae. Dr. E. F. Castetter of the Biology Department of the University of New Mexico contributed valuable.
