STANDLEl TEEES AND SHRUBS OF MEXICO. 951 



Plants simple, usually globular, sometimes short-cylindric, 10 to 12 cm. high 

 when mature, pale bluish green ; ribs low ; areoles woolly when young, circular ; 

 armament very peculiar, at times almost hiding the plant, most of the spines 

 being erect or connivent ; radial spines widely spreading, often as many as 25, 

 usually white, except the tips, these darker, the upper ones 2 cm. long, a little 

 longer than the lower ; central spines 4 to 8, stouter than the radials, at first 

 reddish or black, but becoming grayish blue in age, the lowest turned outward 

 and downward and all more or less curved ; flowei'S 2.5 cm. long, reddish. 



4. Echinomastus macdowellii (Rebut) Britt. & Rose, Cactaceae 3: 151. 1922. 

 Echinocactus macdotcelUi Rebut; Quehl, Monatsschr. Kakteenk. 4: 133. 1894. 

 Northern Mexico. 



Simple, globular or a little depressed, about 7 cm. high, 12 cm. in diameter, 

 covered with a mass of interlocking spines ; ribs 20 to 25, pale green, 5 to 7 

 mm. high, divided into tubercles ; radial spines 15 to 20, white, spreading, up 

 to 1.8 cm. long; central spines 3 or 4, dark colored, the longest up to 5 cm. 

 in length; flowers rose-colored, up to 4 cm. long; ovary globose, said to be 

 scaly. 



5. Echinomastus durangensis (Riinge) Britt. & Rose, Cactaceae 3: 152. 1922. 

 Echinocactus durangensis Riinge, Hamb. Gartenz. 46: 231. 1890. 

 Zacatecas and Durango. 



Simple, ovoid, about 8 cm. long, 7 cm. in diameter ; ribs 18 to 21, low ; are- 

 oles white-woolly when young, biTt without wool when old ; radial spines 15 

 to 30, the lower shorter than the upper, more or less incurved, white except 

 the black tips, 1.5 cm. long ; central spines 3 or 4, a little longer than the 

 radials, acicular, about 2 cm. long. 



35. ECHINOCACTUS Link & Otto, Wochenschr. Ver. Beford. Gartenb. 3: 420. 



1S27. 



Plants very large, thick, cylindric and many-ribbed, or low and several- 

 ribbed, the top clothed with a dense mass of wool or nearly naked ; areoles 

 very spiny, large, those on the upper part of old plants sometimes united ; 

 flowers from the crown of the plant, often partly hidden by the dense wool 

 at the top, usually j^ellow, rarely pink, of medium size; outer perianth seg- 

 ments narrow, sometimes terminating in pungent tips ; inner perianth seg- 

 ments oblong, thinner than the outer, obtuse ; scales on flower tube numerous, 

 imbricate, persistent, pungent ; scales on ovary small, often linear, their axils 

 filled with matted wool; fruit densely covered with white wool, thin-walled, 

 oblong; seeds blackish, smooth, shining, or rarely papillose, with a small sub- 

 basal hilum. 



One other species is known, a native of Utah and Arizona. 



Plants very large, often becoming cylindric. 



Spines all bright yellow 1. E. grusonii. 



Spines brov»^n to gray, rarely some of them yellowish. 



Inner perianth segments linear-oblong, entire 2. E, ingens. 



Inner perianth segments oblong, more or less toothed or lacerate. 



Spines all of one kind 3. E. visnaga. 



Spines both radial and central. 

 Central spine solitary. 



Flowers 4 to 5 cm. long; central spine 4 to 5 cm. long, nearly 



black 4. E. grandis. 



Flowers 3 cm. long ; central spine 3 cm. long, grayish in age. 



5. E. platyacanthus. 

 Central spines several 6. E. palmeri. 



