890 CONTRIBUTIONS FEOM THE NATIONAL HEEBAEIUM. 



areoles but a pseudocephalium is not formed ; in otliers the flowers are pro- 

 duced in a circle at the top and the bristles and fruit afterwards form a 

 collar at tlie base of the new growth ; in otlier species neither wool nor hairs 

 are produced in the flowering areoles ; flowers nocturnal, short-campanulate 

 to short-funnelform or ps'riform, straight or curved ; perianth persisting on 

 the ripening fruit, except in one species ; fruit usually depressed-globose, some- 

 times oblong; seeds black, smooth or tuberculate. 



Numerous additional species occur in tropical and subtropical America. 

 Flowering areoles confluent, forming a pseudocephalium. 

 Pseudocephalium lateral. 

 Plant cylindric, the top rounded; bristles of the pseudocephalium twice 



as long as the wool 1. C. senilis. 



Plant tapering to the apex ; bristles of the pseudocephalium little longer 



than the wool 2. C. hoppenstedtii. 



Pseudocephalium terminal 3. C. macrocephalus. 



Flowering areoles not confluent, not forming a pseudocephalium. 



Ribs 15 to 18; flowers red 4. C. polylophus. 



Ribs 4 to 13; flowers mostly whitish to purplish. 



Flowering areoles without wool or wool very short 5. C. scoparius. 



Flowering areoles definitely long-woolly. 



Ribs only 5 to 6 mm. high 13. C. purpusii. 



Ribs 8 mm. high or higher. 



Plants light or dark green 6. C. gaumeri. 



Plants, at least young joints, blue or bluish green, glaucous. 



Young spines yellow 7. C. chrysacanthus. 



Young spines brown or nearly black. 

 Ribs 9 to 12. 



Wool short, 2 cm. long 8. C. cometes. 



Wool 10 cm. long 9. C. leucocephalus. 



Ribs 7 to 9. 



Flowers rose-red 10. C. sartorianus. 



Flowers brown 11. C. palmeri. 



1. Cephalocereus senilis (Haw.) Pfeiff. Allg. Gartenz. 6: 142. 1838. 



Cactus senilis Haw. Phil. Mag. 63: 31. 1824. 



Cactus hradypus Lehm. Delect. Sem. Hort. Hamb. 17. 1826. 



Cereus senilis DC. Prodr. 3: 464. 1828. 



Pilocereus senilis Lem. Cact. Hort. Monv. 7. 1839. 



EcMnocactus staplesiae Tate; Loud. Gard. Mag. 16: 27. 1840. 



Hidalgo and Guanajuato. 



Plants 6 to 10 or even 15 meters high, columnar, simple or rarely branched 

 above, sometimes branched at base; ribs numerous; pseudocephalium develop- 

 ing on plants when 6 meters high, broadening above, rarely confined to one 

 side but usually encircling the top of the plant; areoles closely set, the 

 ones at base of old plants producing weak gray bristles 20 to 30 cm. long, 

 the ones in the pseudocephalium producing similar but shorter bristles in- 

 termixed with dense, tawny wool, 4 to 6 cm. long; flower (including ovary) 

 5 cm. long, rose-colored ; scales few on the tube ; fruit obovoid, 2.5 to 3 cm. long, 

 rose-colored, capped by the chartaceous base of the flower, bearing a few 

 minute scales with hairs in their axils. " Cabeza de vie jo," " viejo," " viejito." 



This is one of the cacti most cultivated in northern hothouses, where it 

 is known as "old man cactus." The young plants are densely covered witL 

 long white hairs. The species is very abundant on the limestone hills of 

 eastern Hidalgo, where it is often the most conspicuous plant. 



