DISTRIBUTION OF THE MOEE PROMINENT NATURAL ORDERS. 247 



intermediate forms connecting others previously held to be distinct species have been 

 very largely imported *. 



It is impossible to form an approximate estimate of the number of species of 

 Cactacese in South America, where they are generally dispersed up to a high latitude, 

 and where in certain regions, as in Chili and some parts of Peru, they abound to such 

 an extent as to be the greatest scourge and obstacle to travellers that exists. Judging, 

 however, from the numbers given for certain parts, species are not very numerous, 

 though individuals are. Thus, for the whole of Chili Philippi enumerates only fifty- 

 five species f ; and the Cactacese of this part of South America are perhaps better 

 known than those of any other area. GrisebachJ describes seventeen as growing in 

 the British West Indies, and he enumerates fifteen for Cuba §. Of course it is not 

 assumed that these numbers include nearly the whole of the species existing in these 

 islands. Watson || records twenty-nine species from California, chiefly " confined to the 

 south and south-eastern districts." In 1856 Engelmann had cognizance of the occur- 

 rence of 117 species within the United States territories^, and subsequent discoveries 

 have not greatly augmented this number. 



Turning to the general distribution of the order in America, it is found to be mainly 

 western, especially in the northern part of the continent. Excluding two species of 

 Cereus found in the Keys, South Florida, the order is represented east of the Mississippi 

 by only one genus, Opuntia, and four or five species. The latitudinal range of the order 

 is very great, reaching at least the Chonos archipelago about 45° S. on the western side ; 

 and Darwin collected Opuntia darwinii at Port Desire, 47° S., and observed the same 

 at Port St. Julian in 49° S.**. It is the same genus that reaches the northern limit of 

 the order. Three species, according to Macounff, occur in British North America; 

 one as far eastward as Pelee Point, Lake Erie ; and the others in British Columbia, 

 Assiniboine, Saskatchewan, and Athabasca, reaching the Peace river in 56° 12' lat., 

 " where it grows on the arid clay slopes exposed often to a temperature of 55° below 

 zero." The altitudinal range of the order as exemplified in Mexico offers similar 

 extremes, being from the sea-coast up to an elevation of 13,000 feet. Zuccarini JJ and 

 Ehrenberg§§ give the fullest details of the size, distribution, habitats, &c. of the 



* Eorster's ' Handbuch der Cacteenkunde,' zweite Auflage von T. Kiimpler, Yorwort, p. viii. 



f Catalogus Plantarum Chilensium, p. 91. 



X Flora of the British West-Indian Islands, p. 300. 



§ Catalogus Plantarum Cubensium, p. 116. 



|| Botany of California, i. p. 242, ii. p. 449. 



f Proc. Am. Acad. iii. pp. 259-311, 345, 346. 



** Henslow in Jardine's Mag. Zool. & Bot. i. p. 466. 



ft Catalogue of Canadian Plants, p. 177. 



tt Muench. Abhandl. ii. pp. 597-742. 



§§ Lhmaea, xix. pp. 337-368. 



