For numerous helpful suggestions, lists of common flowers, herbarium and fresh specimens for use in preparing illustrations, and for assistance in many other ways, the author and illustrator proffer sincere thanks to the following: Glen Bean, L. Floyd Keller, Walter B. McDougall, and William R. Supernaugh of the National Park Service; Dr. Norman C. Cooper, research associate, Allen Hancock Foundation; Mrs. Robert Gibbs, Isle Royale National Park, Mich.; Leslie M. Goodding, St. David, Arizona; Edmund C. Jaeger, Riverside Junior College, California; Thomas H. Kearney, California Academy of Sciences; Robert H. Peebles (who kindly reviewed the manuscript), director of the U. S. Field Service Station, Department of Agriculture, Sacaton, Arizona; Paul Ricker, president, Wildflower Preservation Society, Washington, D. C.; and Barton H. Warnock, head of biology department, Sul Ross State College, Alpine, Texas. [Illustration: Carnegiea gigantea] Common Names: GIANT CACTUS, (SAGUARO) Arizona desert. (_Carnegiea gigantea_). Waxy white. May-June. Cactus family. Size: Up to 50 feet tall and 12 tons in weight. Largest of the U. S. cacti, this species occurs only in southern and western Arizona and adjoining northwestern Mexico and sparingly in extreme southeast California. It is an indicator of the Sonoran Desert. This giant is such a spectacular example of desert vegetation that it is used as a trademark of the desert. It is the state flower of Arizona. Blossoms unfold at night, remaining open until late the following afternoon, attracting swarms of insects which in turn attract birds. Fruits mature in July, resembling small, egg-shaped cucumbers. When ripe, they burst open revealing a scarlet lining and deep red pulp filled with tiny black seeds. Fruits are eagerly sought by birds and rodents. Because of its enormous capacity for storing water in its spongy stem tissue, the Saguaro (sah-WAR-oh) produces flowers and fruits even during droughts of long duration. When other foods failed, the Pima and Papago Indians could depend upon the Saguaro harvest. [Illustration: Dry weather, Rainy weather] [Illustration: skeleton, flesh] Saguaros are believed to live to a maximum age of 200 years, usually succumbing to a necrosis disease transmitted by the larvæ of a small moth. Grazing cattle trample out the young plants and much of the desert occupied by Saguaros is being placed under cultivation. Both Saguaro National Monument and Organ Pipe Cactus National Monument preserve and protect spectacular stands of these desert behemoths. WHITE [Illustration: Peniocereus greggi] Common Names: NIGHTBLOOMING CEREUS, (_Reina-de-la-noche_) Arizona and Texas deserts. (_Peniocereus greggi_). White. June-July. Cactus family. Size: 2 to 5 feet tall.