202 



An interesting tabulation could be made by those interested in 

 endemism on the number of prickly pears with a relatively 

 restricted distribution. Scores have been found only in isolated 

 regions, a few scattered through neighboring cactus deserts, 

 still fewer of very general distribution in tropical America, of 

 which Opuntia ficus-indica seems to be the most ubiquitous.* 

 As the group is wholly American, the distribution in North or 

 South America, or in the West Indies, plotted out as to the apparent 

 centers of distribution of some of the significant species, would be 

 of particular interest. As a partial aid to such an understanding, 

 the reviewer lists the chief cactu's regions of the area covered by 

 the book with the number of species recorded from there by the 

 authors. 



Southwestern United States and adjacent Mexico 63 



Mexico and Central America 62 



The Argentine, including Paraguaj', Uraguay & Chile 61 



As between these two great centers of cactus species, for the 

 first two are probably inseparable, the links are very few and 

 scattered. The authors record only three species that are 

 common, as natives, to both regions and are found in the inter- 

 vening area. There are, of course, other prickly pears between 

 these two great centers as, for instance, 12 in Bolivia, 14 in 

 Peru, 9 in Ecuador, 7 in Brazil, 5 in Colombia, and 4 in Venezuela 

 and adjacent islands. 



These 56 species, endemics nearly all, and often separated by 

 rain forests, seem a somewhat slender thread to stretch across the 

 three or four thousand miles between the northern and southern 

 culminations of the cactus flora. As a matter of record, the 

 figures for the rest of the genus are given herewith. West Indies 

 15, Bahamas 4, Tropical America generally 3, Southeastern 

 United States 11, Central United States 6, Northeastern United 



* An interesting case of apparent endemism is that of 0. SkoUsbergii, a species 

 described as new in the book. It is native in Santa Cruz territory in the Argentine, 

 and, apparently unknown to the authors, was described briefly, it is true, by Skotts- 

 berg in his Die Vegetationsverhaltnisse Langs der Cordillera de los Andes, which 

 was published on April 26, 1916, in Kungl. Sv. Vetenskapsakadcmicns Handlingar, 

 Band 56, no. 5, at page 268. Dr. Skottsberg credits the species to the authors of 

 the present volume, so there is fortunately only a question of priority of publica- 

 tions involved in the case, not another name added to the nine hundred! 



