THE CACTACEAE. 



nearly white margins, widely spreading or even turned back at the apex, broad, obtuse; filaments 

 short, numerous, erect, white, borne all over the throat, 2 to 2.5 cm. long; lower part of flower-tube 

 or tube proper smooth within; ovary tuberculate, bearing small, ovate, acute scales, these with 

 white and brown hairs in their axils; fruit globular, 4 to 7.5 cm. in diameter, edible, very spiny, but 

 in age naked, olive without, crimson within; seeds black, shining, 1.8 to 2 mm. long. 



Type locality: Canyon near the mountain pass of Bachuachi, Sonora, Mexico. 



Distribution: Southern Arizona, in the Comobabi, Quijotoa, and Ajo Mountains, 



throughout western Sonora, and on both coasts of Lower California. The Index Kew- 



ensis says it is from New Mexico, doubtless an error for northern Mexico. In the cape 



region of Lower California a slender form is found which has been described as a variety. 



The flowers, which appear from March 

 to August, are followed by the large delicious 

 fruit much prized by the native, who knows 

 it as pitahaya or pitahaya dulce. 



Kig. 143. — Lemaireocereus thurberi. 



Fig. 144. — L. thurberi: a, flower; b, fruit. X0.7. 



The species was named for George Thurber (i 821 -1890), one of the collectors on 

 the first Mexican Boundary Survey. 



The habit of branching just at the base is unusual in this genus, in which most of the 

 species have definite, though often short, trunks. 



This is the only species of Lemaireocereus which reaches the United States and is the 

 only one found in northwestern Mexico or Lower California. Two other species were 

 credited to Lower California in our former treatment (Contr. U. S. Nat. Herb. 12: 425), 

 but these we now refer to another genus (see pages 115, 116). 



Whether the flowers open at night or during the day has been in dispute. Dr. Rose, 

 who studied the species in Lower California, observed the flowers widely expanded at 2 

 o'clock on a bright sunny day. F. E. Lloyd, in a letter dated September 6, 1909, says, 

 "I notice that what we have hitherto called Cereus thurberi is stated by you as having a 

 day-blooming flower. You may recall that I made a special study with reference to this 

 point at the Quijotoa Mountains and found it strictly night-blooming. The photograph 

 which you have of the flower I made between 4 and 5 o'clock in the morning, just before 

 sun-up." 



Cereus thurberi monstrosus (E. Dams, Monatsschr. Kakteenk. 14: 182. 1904) is not an 

 unusual form. 



