460 
Spines mostly solitary. 
Longest spines not exceeding | to 2.5 em. 
kleiniw (95), arbuscula (96), leptocaulis (97). 
Longest spines 5 to 6 em, 
. stipata (98), vaginata (99), ramosissima (100). 
GEOGRAPHICAL DISTRIBUTION. 
The genus Opuntia is far more largely represented in the United 
States than any other genus of Cactacer, extending into British 
Columbia and to the Atlantie Seaboard and displaying a maze of forms 
in the Southwestern States. This is specially true of PLATOPUNTIA. 
The great uncertainty as to the species of Opuntia is probably aecount- 
able for the large enumeration of them peculiar to our flora. Numer- 
ous fornis have never been recognized a second time, and others are 
kept distinct from each other and trom Mexican forms when they should 
doubtless be merged. In almost every unvisited locality “new species” 
are found so freely that no confidence can be placed in our conception 
of specific lines in this genus. The following discussion is based upon 
the presentation of the previous pages, but it should be understood 
that it must be largely modified by a fuller understanding of the genus. 
The two sections, PLATOPUNTIA and CYLINDROPUNTIA. are so dis- 
tinet from each other that they will be considered separately. 
CYLINDROPUNTIA, with 28 forms enumerated as belonging to our 
flora, but 11 of which ave restricted to the United States. does not 
extend north of central Colorado or east of Texas. It is preeminently 
a Sonoran and Lower Californian type, and 25 of the 28 forms oceur in 
the desert region of western Arizona and southern California. Of the 
17 forms in common with the Mexican flora 15 are now traced into 
Sonora and Lower California, and the others certainly will be. Further 
exploration of those Mexican States will doubtless reduce the number 
of species now enumerated as peculiar to our flora. The 11 forms 
regarded at present as endemic are distributed as follows: echinocarpa 
parkeri, serpentina, and bernardina in southern California, and doubt- 
less of Lower Californian origin; ihipplei spinosior and versicolor in 
southern Arizona, certainly to be found in Sonora: parryi, clavata, and 
pulchella more isolated in southern Nevada and adjacent regions; 
davisti extending from southern California to southern Colorado and 
northwestern Texas; and grahami, a low-ground species, found along 
the Rio Grande bottoms from El] Paso downward, and schottii, found 
as yet only in Texas between the San Pedro and Pecos, the two 
species of our endemic Cylindropuntias which do not indicate a lower 
Californian or Sonoran connection. 
The seventeen Cylindropuntias in common with Mexico are, with two 
exceptions, all found in the desert regions of southern California and 
Arizona, some of them extending into Nevada, others further eastward 
into Utah and Colorado, and some reaching Texas. They occur in two 
types, the more robust and more spiny forms (such as echinocarpa, proli- 
