68 THE CACTACEAE. 



It is a most troublesome plant to come in contact with, for, as the sharp, barbed spines 

 pierce the flesh, the joints easily break loose from the plant and are detached with difficulty 

 from the unfortunate victim. 



The flowering season extends from early spring to September. The fruit is markedly 

 proliferous, often developing in chains, and so persisting for several years, possibly eight 

 or ten years, as suggested by Professor D. S. Johnson. They grow in chains of 8 or 9 

 fruits (12 to 14 have been reported), several chains hanging from a single joint and forming 

 a large cluster. We have seen as many as 38 fruits (40 to 50 have been reported) in a 

 single cluster, ,and doubtless under favorable conditions many more would be found. 

 These juicy fruits, usually spineless, are much sought by grazing animals. 



According to Professor Johnson, who has studied this species several years, the seeds 

 are not known to germinate in nature. Only by cutting away a part of the hard, bony coat 

 could they be made to germinate in the greenhouse. The species is propagated easily 

 by the terminal joints, which come off readily and are transported far and wide like burs, 

 and soon strike root on reaching the soil. New plants are also started occasionally by the 

 fruits themselves. 



This species appears to hybridize with 0. spinosior. 



Illustrations: Ariz. Agr. Hxp. Sta. Bull. 67 : pi. i, f. 2; Bull. Torr. Club 32 : pi. 9, f. i ; 

 Cact. Mex. Bound, pi. 75, f. 18; Card, and For. 8: f. 46; Hornaday, Camp-fires on Desert 

 and Lava opp. p. 42, 320; Lumholtz, New Trails in Mex. opp. p. 18; Monatsschr. Kakteenk. 

 18: 153; Nat. Geogr. Mag. 21: 710; N. Mex. Agr. Exp. Sta. Bull. 60: pi. 6, f. 2; Plant 

 World u e : f. i, in part; ii'": f. 9, in part; Sargent, Man. Trees N. Amer. f. 559; Ariz. Agr. 

 Exp. Sta. Bull. 67: pi. 5, f. i; Cact. Mex. Bound, pi. 75, f. 19; Lumholtz, New Trails in 

 Mex. opp. p. 152; Nat. Geogr. Mag. 21 : 710; Plant World n 1 ': f. i, in part; n 10 : f. 9, in 

 part, the last six as Opuntia mamillata; Carnegie Inst. Wash. 269: Frontispiece; pi. i to 

 7; pi. 8, f. 76 to 79; pi. 12. 



Plate ix, figure 6, represents the proliferous fruit ; plate xn, figure i , is from a photo- 

 graph taken by Dr. MacDougal near Tucson, Arizona, showing the typical plant to the 

 left and the less spiny plant to the right. 



31. Opuntia spinosior (Engelmann) Tourney, Bot. Gaz. 25: 119. 1898. 

 Opitntia u'hipplci spinosior Engelmann, Proc. Amer. Acad. 3 : 307. 1856. 



Plants 2 to 4 meters high, tree-like in habit, with a more or less definite, woody trunk, openly 

 branched; ultimate joints i to 3 dm. long, 1.5 to 2.5 cm. in diameter, often bright purple, 

 strongly tuberculate; tubercles about 6 to 12 mm. long, longer than broad, more or less flattened 

 laterally; spines 6 to 12, but on old branches sometimes as many as 25, 10 to 15 mm. long, diver- 

 gent, gray to brownish, covered with thin sheaths; glochids yellowish white; flower-buds short, 

 acute; flowers 5 to 6 cm. broad, purple to pink, ye'low, or even white; petals about 10, broad at 

 apex, narrowed at base; style thick, cream-colored or pinkish; ovary tuberculate, bearing small, 

 purple leaves and long, white, easily detached bristles; fruit strongly tuberculate, spineless, yellow, 

 globose to broad'y oblong, 2.5 to 4 cm. long, with a depressed umbilicus; seeds white, 4 mm. broad, 

 smooth, with a very indistinct marginal band. 



Type locality: South of the Gila River. 



Distribution: Arizona, western New Mexico, and northern Mexico. 



Opuntia spinosior neomexicana (Tourney, Bot. Gaz. 25: 119. 1898) seems to be a 

 yellow-flowered form of this species. Mr. Tourney writes that his original material of 

 this variety came from the low foothills north of the Rillito River near Tucson. 



Opuntia spinosior was described by Engelmann in 1856 as a variety of 0. whipplci, to 

 which it is only remotely related, but it was not separated until 1898, when it was described 

 as distinct by Professor J. W. Tourney. 



Illustrations: Ariz. Agr. Exp. Sta. Bull. 67 : pi. i, f. i ; pi. 5, f. 2 ; Gard. and For. 9 : f . i ; 

 N. Mex. Agr. Exp. Sta. Bull. 60: pi. 7, f. i; Plant World n 10 : f. 7; Sargent, Man. Trees 

 N. Amer. f. 560. 



