INTRODUCTION. 5 



In 19 1 5 Dr. Rose, accompanied by Paul G. Russell, visited Brazil and Argentina 

 on the east coast of South America, collecting extensively in the semiarid parts of 

 Bahia, Brazil, and in the region about Rio de Janeiro, so rich in epiphytic cacti. 

 In the deserts about Mendoza and Cordoba, in Argentina, collections were also 

 made. Here he also arranged for exchanges with the leading botanists and collec- 

 tors. The following persons have made valuable contributions from the regions 

 visited: Dr. Leo Zehntner, Joazeiro, Brazil; Dr. Alberto Lofgren, Rio de Janeiro, 

 Brazil; Dr. Carlos Spegazzini, La Plata, Argentina; Dr. Cristobal M. Hicken, 

 Buenos Aires, Argentina; and Dr. Carlos S. Reed, Mendoza, Argeritina. 



In October and November 1916, Dr. Rose, accompanied by Mrs. Rose, visited 

 Curasao and Venezuela, studying especially the cactus deserts about La Guaira 

 and Puerto Cabello. A number of photographs were taken by Mrs. Rose. 



While en route for Venezuela, arrangements were made with Mr. Harold G. 

 Foss to make a collection of cacti at Coro, Venezuela. Among the specimens 

 obtained were species not found farther east in Venezuela, so far as known. 



In 1916 Dr. Britton, assisted by Mr. Percy Wilson, studied the cacti of Havana 

 and Matanzas Provinces and those of the Isle of Pines, Cuba. 



In 1918 Dr. Rose, assisted by George Rose, visited Ecuador on behalf of the 

 United States Department of Agriculture, aided by the Gray Herbarium of Har- , 

 vard University and the New York Botanical Garden ; about thirty rare or little- 

 known species were obtained. 



Through the expenditure of about $2,400, contributed by Dr. Britton, a very 

 important collection of cacti was made by JDjL-J^^A^^jiafer during a six months' 

 exploration from November 1916 to April 19 17 of the desert regions of northwestern 

 Argentina, southeastern Bolivia, northeastern Argentina, and adjacent Uruguay 

 and Paraguay. Fortunately, for the purposes of this work, this collection was 

 ^Drought back to New York by Dr. Shafer in time for the information yielded by 

 it and by his field observations to be used in the manuscript. It has given us-^ 

 first-hand information concerning over 120 species of cacti as to which we have - 

 previously known little. 



There are still a few cactus regions which ought to be explored, but the following 

 summary will show the wide field from which we have obtained information. 



Our field investigations have covered practically all the cactus deserts of 

 Mexico. The most important of these are the vicinities of Tehuacan and Tomellin, 

 the plains of San Luis Potosi, the chalky hills surrounding Ixmiquilpan, the lava 

 fields in the Valley of Mexico and above Cuernavaca, the deserts of Oueretaro, the 

 west coast of Mexico extending from the United States border to Acaponeta, and 

 the seacoasts and islands of Lower California. Other regions in Mexico containing 

 cacti, but not in such great abundance as the foregoing, are those about Pachuca, 

 Oaxaca City, Mitla, Jalapa, Iguala, Chihuahua City, and Guadalajara. All the'/' 

 work in Mexico, however, was done prior to 19 12, for, owing to political disturb-*^ ^4 

 ances, no field work there has been feasible since that time.jJt^-- 



In the United States our work has extended over the cactus regions of Florida, 

 Texas, New Mexico, Arizona, southern California, western Kansas, and south- 

 eastern Colorado. 



