440 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 



Spines more numerous, 2 to 5 cm. long, diva- 

 ricate, or the two lowest appressed, some- 

 what flattened, whitish, or at least pale. 



Fruit oblong to clavate, large 24. 0. engelmanni. 



Fruit spheroidal, small 32. 0. cyclodes. 



Plants prostrate and mainly widely spreading, at most 

 ascending, usually only the one or two terminal 

 joints erect, mostly under 30 cm. high, sometimes 

 forming irregular beds of an area of several square 

 meters. 

 Spines mostly white or pale, at most yellow or yellow- 

 ish brown at base or tip; joints mostly small, 15 

 cm. long or less, of various shapes. 

 Plants small, usually consisting of only a few joints, 

 these 6 or 7 cm. long; spines slender, 3 to 5 cm. 

 long; glochids yellow, very long on the edges 



of young joints; flowers red 31. 0. filipendula. 



Plants larger, often of numerous joints 8 to 15 cm. 

 long; spines various; glochids usually not promi- 

 nent, except on old joints, then very numerous; 

 flowers yellow. 

 Joints spiny only on the upper marginal areoles..25. 0. stenochila. 

 Joints spiny almost throughout. 

 Spines mostly 2 to 4 cm. long (plants resembling 

 0. polyacantha, but with pulpy fruit); 

 some of the joints nearly orbicular, 8 to 10 

 cm. long;' seeds larger, about 6 mm. in di- 

 ameter; roots fibrous 26. 0. ajmochila. 



Spines longer, 3 to 6 cm. long, slender; joints 

 narrowly obovate, 10 to 15 cm. long or even 

 larger; seeds smaller, 3.5 to 4 mm. in diame- 

 ter; roots sometimes tuberous 27. 0. tenuispina. 



Spines darker, stouter, light brown or dark brown, 

 sometimes lighter at the tip or with age; joints 

 mostly about 15 cm. long, sometimes larger, obo- 

 vate, often broadly so, or the older joints almost 

 orbicular. 

 Spines yellowish brown at the base, lighter toward 

 the tip, the lateral spines usually lighter col- 

 ored and more or less appressed 28 . . toumeyi. ' 



Spines darker colored, mostly dark brown, widely 



spreading, 5 to 6 cm. long, or even more, rarely 



if ever appressed. 



Glochids on old joints very abundant and large, 



10 to 12 mm. long; plant of the southern part 



of the State 29. O. chihuahuensix. 



Glochids less numerous and shorter; plant of the 



north-central part of the State 30. 0. camanchica. 



In the treatment here given there is some uncertainty about several of the species, 

 the degree and character of the doubt being expressed in the notes following the 

 separate species, which should be consulted. 



Just what Opuntia phaeacantha brunnea Engelm. is we are unable to determine. It 

 is probably a form very similar to that here referred to 0. toumeyi Rose, but should be 

 an erect, spreading plant, similar to the species. 



