Illustrations no. 212–218, 220–223, 229–231, 235–238 and 241–243—N. L. Britton and J. N. Rose, The Cactaceae, vols. I—III (courtesy of the Carnegie Institution of Washington); no. 414—417, 419–425, 429–433, 438, 441–444, 447–457 and 459–461—Oakes Ames and Donovan Stewart Correll, Orchids of Guatemala, Fieldiana: Botany, Vol. 26, Nos. 1 and 2 (Courtesy of the Field Museum of Natural History, Chicago).
The following also provided selected illustrations: Macmillan, Ltd. (London); State of Kansas Cooperative Extension Service, Kansas State University; State of Michigan Cooperative Extension Service, Michigan State University; State of New York Cooperative Extension Service, Cornell University; Douglas and Doris Swarthout of Berry Hill Bookshop, Deansboro, N.Y.; and United States Department of Agriculture, Cooperative Extension Service.