554 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1908. 



ribs, which bear the areoles, while in H. triangularis the areoles are 

 borne in the notches of the crenations of its compressed wing-like ribs. 



Selinocereus, with large white fragrant night-blooming flowers, 

 includes the queen-of-the-night cactus {G evens grandifonis)^ known 

 in Tamaulipas, Mexico, as organillo: the common "night-blooming 

 cereus" of our conservatories, Cereus pteranthus {C. nycticalus 

 Link), and Cereus hamatus^ with remote hook-like processes along 

 the ribs. 



Acanthocereus, as treated by Schumann, has a single species which 

 has received various names: Cereus frinceps Pfeitf., Cereus variabilis 

 Engelm. (not Pfeiff.), and Cereus haxardensis Karw. It has now 

 been identified as Linnaeus's Cactus pentagonus^ and should there- 

 fore be called Acanthocereus pentagonus Britt. and Rose. It is a 

 night-flowering cactus with erect or reclining 3 to 6 angled stems, the 

 areoles distant, bearing 4 to 6 stout, radiating, unequal spines. The 

 flowers have long tubes, green sepals and white petals; the oval 

 spiny fruit (pitahaya) is bright scarlet with thick black seeds and 

 luscious red pulp. This species occurs on both sides of the Rio 

 Grande and extends southward along the Mexican coast into Central 

 America. It also occurs in the West Indies. 



Heliocereus, with crimson or purple-red flowers, includes the well- 

 known Cereus speciosus of conservatories and the very closely allied 

 C. coccineus and C. schrankii. In the state of Jalisco H. speciosus is 

 sometimes called Santa Maria, or xoalacatl. It has large purple-red 

 flowers with an iridescent bluish center, which remain open for 

 several days. The 3 to 5 ribs are serrated, the areoles occupying the 

 short upper side of the serrations, bear white wool and clusters of 

 5 to 8 stiff, slender, sharp-pointed spines, the under one yellow and 

 bristle-like. 



Wilcoxia includes two slender-stemmed species with large fleshy 

 roots: Cereus poselgeri {Cereus tuberosus Poselg.), called sacasil in 

 Nuevo Leon, with stems as thick as a lead pencil, purple flowers, and 

 woolly fruit bearing black and white bristles; and Cereus striatus, 

 with stems no thicker than straws, soft harmless spines, purple flow- 

 ers, and scarlet spiny fruit. The latter species was collected by 

 Dr. Edward Palmer on Carmen Island, Gulf of California. It occurs 

 on the peninsula of Lower California and in Sonora, where its com- 

 mon name is sacamatraca, saramatraca, or pitayita. It is identical 

 with the plant described by Weber as Cereus diguetii. 



Aporocactus includes the slender stemmed rat-tail cactus, Cereus 

 fagelliformis (fig. 18), with beautiful rose-colored or crimson zygo- 

 morphic flowers, which are sold in the drug markets of Mexico under 

 the name of flor de cuerno, for use as medicine. 



Echinocereus is characterized by diurnal flowers, comparatively 

 short and rarely tubular. The ovary and tube bear prickly and woolly 



