68 EXPLANATION OF PLATES. 
Pr. 69. Opuntia MAcroruiza: 1, a whole plant with flower and buds, half natural size; 2, 
fruit natural size ; 8-4, seeds of different size. 
Pr. 70. Opuntia Emoryt, from the region southwest of El Paso, in fruit. 
Pu. 71. The same: 1, a whole plant, reduced ; 2, lateral view of a tubercle with a bunch of 
spines; 3, front view of one of the largest bunches of spines; part of the central spine, four 
times magnified ; 4, different seeds. 
Pu. 72. Oruntta Granamr: 1, whole plant, with large tuberous roots, and in fruit; 2, a 
young joint; 3, a bunch of spines of the usual form; 4, another one with broader central 
spines; 5, seed. The seed, as well as parts of spines, are four times magnified. 
Pu. 73, Fra. 1-3. Opuntia Scnormr: 1-2, bunches of spines, with parts four times magnified 
3, seed with an oblique embryo. 
Fie. 4. Opuntia Scnorrir, var. Greece: a bunch of spines, with part magnified four times. 
Fic. 5-6. OpuNnTIA BULBISPINA: 5, an entire joint; 6, a bunch of spines, part of central spine 
four times magnified. 
Fig. 7-8. OPUNTIA IMpRicaTA: 7, a joint; 8, a bunch of spines, and fragment of central spine, 
four times the natural size, showing the sheath. 
Pu. 74. Seeds of—1, Mamillaria calcarata; 2, Mamillaria compacta; 3, Mamillaria vivipara ; 
4, Mamillaria radiosa, var. borealis; 5, Mamillaria radiosa, var. Texana; 6, Mavillaria nutallis 
a borealis; 7, 2 cespitosa ; 8, Mamillaria robusti spina; 9, Echinocactus uncinatus ; 10, Echi- 
nocactus uncinatus, var. Wrightii; 11-14, Echinocactus sinuatus; 11, from the San Pedro, 
Wright ; 12, from northern Mexico, Gregg ; 13, from the same regions, Poselger; 14, the form 
sent by Poselger under the name of Echinocactus robustus; 15, Cereus Thurberi ; 16, Cereus 
Schottii. 
Pu. 75. Seeds of Opuntia : 1-4, Opuntia Engelmanni ; 1, from Chihauhua, Wislizenus ; 2, 
from Matamoras; 3, from Presidio, Bigelow; 4, from Santa Rosa, Bigelow; 5—7, Opuntia dulcis, 
Wright and Bigelow; 8, Opuntia macrocentra, Wright ; 9-13, Opuntia pheacantha ; 9, from 
Santa Fé, Fendler; 10-13, Southern New Mexico, Wright ; 14, Opuntia tenuispina, El Paso ; 
15, Opuntia arenaria, El Paso ; 16-17, Opuntia arborescens ; 18, Opuntia fulgida ; 19, Opuntia 
mamillata. 
The maps accompanying this memoir represents the geographical distribution of the different 
species of cactacece in the United States and a regions, as far as at present known. 
