CACTACE^ OF MEXICO SAFFORD. 543 



shell. In Pereskiopsis they are covered with matted hairs or cotton. 

 In Opiintia and Nopalea they are fiat, hard, and bony, often iiiargined 

 and more or less ear-shaped in flat-jointed Opuntias (fig. 9^), or dis- 

 coid and marginless, as in many cylindrical-jointed Opuntias (fig. 9^). 

 In Cereiis they are glossy black, either quite smooth or finely pitted 

 (fig. 9"), while in Echinocereiis they are covered with minute 

 tubercles (fig. 9*). In Echinocactus they are pitted in some species 

 and tuberculate in others. In Rhipsalis cassytha, they are kidney- 

 shaped and finely granular. In one section of Mamillaria (Eumamil- 

 laria) they are glossy and marked with sunken rounded pits (fig. 9^) ; 

 in another section (Coryphantha) they are frequently smooth; while 

 in Ariocarpus, which is quite close to Mamillaria, they are com- 

 paratively large and tuberculate. In the little Pelecyphora asellifor- 

 mis they are kidney-shaped, while in P. pectinata they have a peculiar 

 boat-like form with a very large umbilicus. The seeds of nearly all 

 Pachj^cerei (cardones) are used by the Indians for 

 food. The " higos de tetetzo " of southern Puebla 

 {Pachycereus columna-trajanio, are a regular food 

 staple and are to be found in the markets of Tehua- 

 can in the month of May. 



CLASSIFICATION. 



Beginning with Pereskia, which most nearly 

 resembles other dicotyledonous plants, and which 

 in all probability approaches the ancestral type of 

 the familj?-, Schumann divides the Cactacese into 

 three subfamilies: (I) Pereskioideae, consisting of 

 the single genus Pereskia; (II) Opuntioidea?, 

 composed of Opuntia and its allies; and (III) 

 Cereoideae, divided into two tribes, (1) EcMnocacteae^ including 

 Cereus, and its allies, Echinocactus^ Leuchtenbergia^ Melocactus, 

 Phyllocactus Epiphyllum., Hariota^ and Rhipsalis; and (2) Mamil- 

 lamece^ including Mamillaria^ Pelecyphora^ and Ainocarpus. 



With a few exceptions the genera and subgenera of Cactacese, as 

 treated by early writers, are not sharply separated by definite limits. 

 In many of them there are transition species which have character- 

 istics of two genera or subgenera. Thus there are species of Echino- 

 cactus very closely resembling certain Mamillarias (Coryphanthse) in 

 their structure, and the relationship of several of the columnar Cerei 

 is not clear. Various authorities have divided the old genera of 

 Opuntia, Cereus, Echinocactus, and Mamillaria into groups, some- 

 times regarding them as distinct genera, sometimes as subgenera, or 

 "series." Many of these closely allied groups difi^er radically from 



5 



Fig. 9. — Cactus seeds. 



