CACTACE^ 685 



pistil of several united carpels ; ovary 1-cellecl, with several parietal placentas ; 

 styles united, terminal ; stigmas as many as the placentas ; ovules numerous, 

 horizontal, anatropous. Fruit a fleshy berry. Seeds numerous, with albumen ; 

 cotyledons foliaceous ; radicle turned toward the hilum. 



The Cactus family with twenty genera and a very large number of species 

 is most abundant in the dry region adjacent to the boundary of the United 

 States and Mexico, with a few species ranging northward to the northern 

 United States and southward to the West Indian islands, Brazil, Peru, and 

 the Galapagos Islands. Two of the genera have arborescent representatives in 

 the flora of the United States. 



CONSPECTUS OF THE ARBORESCENT GENERA OF THE UNITED STATES. 



Branches and stems columnar, ribbed, continuous ; leaves ; flower-bearing- and spine- 

 bearing- areolfe distinct ; flowers close above spine-bearing areolae ; tube of the flower 

 elongated; seeds dark-colored. 1. Cereus. 



Branches jointed, tuberculate ; leaves scale-like ; flower-bearing and spine-bearing areolae 

 not distinct ; tube of the flower short and cup-shaped ; seeds pale. 2. Opuntia. 



1. CEREUS, Haw. 



Trees or shrubs, with columnar ribbed stems, and buds on the back of the ridges 

 from the axils of latent leaves, geminate, superposed, the upper producing a brancli 

 or flower, the lower arrested and developed into a cluster of spines surrounded by 

 an elevated cushion or areola of chaffy tomentose scales. Flowers lateral, elongated, 

 the calyx lobes forming an elongated tube, those of the outer ranks adnate to the 

 ovary, scale-like, only their tips free, those of the inner ranks free, elongated 'petals 

 cohering by their bases with the top of the calyx-tube, larger than its interior lobes, 

 spreading, recurved ; stamens numerous; filaments adnate by their base to the tube 

 of the calyx, those of the interior ranks free, the exterior united into a tube ; style 

 filiform, divided into numerous radiating linear branches stigmatic on the inner 

 face; stalks of the ovules long and slender, becoming thick and juicy in the fruit. 

 Seeds with very thin albumen; embryo straight; cotyledons abbreviated, hooked at 

 the apex; radicle conical. 



Cereus with about two hundred species inhabits the dry southwestern region of 

 North America, the West Indies, tropical South America, and the Galapagos Islands. 

 Of the numerous species found within the territory of the United States only one 

 assumes the habit and size of a tree. The fruit of several species is edible, and the 

 ribs of the durable woody frames of the stems of the large arborescent species are 

 used for the rafters of houses and for fuel. Many of the species are planted in 

 warm dry countries in hedges to protect cultivated fields, and others are popular 

 garden plants valued for their beautiful flowers, which are sometimes nocturnal and 

 exceedingly fragrant. 



The generic name relates to the candle-like form of the stem of some of the 

 species. 



1. Cereus giganteus, Engelm. Su-warro. 



Leaves 0. Flowers 4'-4^' long and 21' wide, opening from May to July in great 

 numbers near the top of the stem, each surrounded on the lower side by the radial 

 spines of the cluster below it; ovary ovoid, 1' long, rather shorter than the stout 

 tube of the flower, and covered, like the base of the tube, by the thick imbricated 

 green outer scale-like sepals, with small free triangular acute scarious mucronate 



