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 ^-ictim. 



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

 proliferous, often developing in chains, and so persisting for several j^ears, possibly- eight 

 or ten 3-ears, as suggested by Professor D. S. Johnson. They grow in chains of 8 or 9 

 fruits (12 to 14 have been reported 1, 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 vmder favorable conditions many more would be foimd. 

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



According to Professor Johnson, who has studied this species several j^ears, the seeds 

 are not known to germinate in nature. Only by cutting awaj- a part of the hard, bon}^ coat 

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

 bv the terminal joints, which come off readil}' and are transported far and wide Hke burs, 

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

 fruits themselves. 



This species appjears to hybridize with O. spinosior. 



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

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

 and Lava opp. p. 42, 320; Lumlioltz, New Trails in IMex. opp. p. 18 ; ]SIonatsschr. Kakteenk. 

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

 World II®: f. i, in part; 11^'- : 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 11^: f. i, in part; 11" : f. 9, in 

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

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



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

 graph taken b^- Dr. MacDougal near Tucson, Arizona, showing the t5^ical plant to the 

 left and the less spin}- plant to the right. 



31. Opuntia spinosior (Engehnann) Toiunej^ Bot. Gaz. 25: 119. 1898. 

 Opuniia whipplei spinosior Engetmaim, 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 man}^ 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, yelow, 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, easUy detached bristles ; fruit strongly tuberculate, spineless, j^ellow, 

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

 smooth, with a verj^ indistinct marginal band. 



Type locality: South of the Gila River. 



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



Opuniia spinosior neomexiiana (Toume}', Bot. Gaz. 25: 119. 1898) seems to be a 

 yeUow-flowered form of this species, ilr. Tomne^' writes that his original material of 

 this variet}- came from the low foothills north of the RiUito River near Tucson. 



Opuniia spinosior was described by Engelmann in 1S56 as a variet}^ of 0. ii'hipplei, to 

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

 as distinct by Professor J. W. Toumey. 



Illustrations: Ariz. Agr. Exp. Sta. BuU. 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 11^*^' : f. 7; Sargent, :Man. Trees 

 N. Amer. f. 560. 



