CACTACEJ5 OF MEXICO SAFFORD. 



537 



Mexican gentleman, Don Jose Artolozaga, ^vho invited me to accom- 

 pany him on an expedition to the magnificent presa of San Luis 

 Potosi, of which I have spoken above. 



I shall now attempt to give a short account of the Cactacea3 in 

 general, their geographical distribution, wonderful adaptation to 

 various conditions of soil and climate, their vegetative and floral 

 characteristics, and the economic uses to which many of the species 

 are applied. 



Geographical Distribution or Cactace.e. 



The Cactacese are almost entirelj^ confined to America, the only ex- 

 ception being the genus Rhipsalis, the i^lants of which are epiphytes, 

 Avith j)ellucid, glutinous berries, manj^ of 

 them resembling rather mistletoes than 

 cacti. It is quite possible that they may 

 have been disseminated, like mistletoe, 

 through the agency of birds. 



Several prickly pears introduced at an 

 early date into Europe and Africa have 

 established themselves on both sides of 

 the Mediterranean, and more recently in 

 south Africa ; and in certain regions of 

 Australia introduced species are crowd- 

 ing out the indigenous vegetation to such 

 an extent that they have come to be re- 

 garded as pests. It is quite common to 

 regard all cacti as tropical or semitrop- 

 ical, but there are a number of species 

 which withstand the frosts of winter. 

 At least two Opuntias extend northward 

 into British Columbia,* and species of 

 Echinocereus, Echinocactus, and Mamillaria are included in the 

 flora of Colorado.^ 



For a comprehensive account of the vegetation of the deserts of our 

 so^ithwestern States and of Mexico the reader is referred to Professor 

 Frederick V. Coville's Botany of the Death Valley Expedition, pub- 

 lished as volume 4 of the Contributions from the United States 

 National Herbarium, 1893 ; and to Dr. D. T. MacDougal's '' Botanical 

 Features of North American Deserts," Publication No. 99 of the 

 Carnegie Institution of Washington, 1908. 



To the southward the family extends to Chile and Argentina. 

 Giant torch thistles and Echinocacti are scattered over the pampas 



« See Piper, C. V. Flora of the State of Washington, p. 396. 1906. 

 ^ See Rydberg, P. A. Flora of Colorado, p. 237. 190(J. 



Fig. 1. 



—Mistletoe cactus {Rhip- 

 salis cassytha). 



