66 



THE CACTACEAE. 



Key to Species. 



A. None of spines hooked (1-104, 150). 

 B. Seeds brown (1-80). 



C. Tubercles giving off milk freely when pricked or cut (1-53). 

 D. Axils of tubercles without bristles (1-33). 

 E. Tubercles more or less elongated. 

 F. Tubercles terete throughout. 

 Spines yellow or reddish. 



Spines red i. N. mammillaris 



Spines yellow 2. N. iiivosa 



Spines usually white except tips, at least not red or yellow. 

 Central spines i or 2. 



Central spines about length of radials 3. A', gavmeri 



Central spines much longer than radials 4. jV. petrophila 



Central spines 4 to 7. 



Outer perianth-segments entire; central spines long, slender 5. N. arida 

 Outer perianth-segments erose; central spines not elon- 

 gated, stouter than in preceding species . 6. N. brandegeei 

 FF. Tubercles more or less angled. 



G. Tubercles nearly terete towards apex. 



Outer perianth-segments and scales more or less fim- 

 briate. 



Flowers reddish 7. N. gummifera 



Flowers light yellow 8. N. macdougalii 



Outer perianth-segments and scales entire. 



Radial spines white; flowers pinkish 9. N. heyderi 



Radial spines brownish; flowers white to cream- 

 colored. 

 Plant hemispheric; radial spines 9 to 13; perianth- 

 segments acute 10. N. hcmisphaerica 



Plant much flattened; radial spines 18 or fewer; 



perianth-segments acuminate 11. N. applanala 



GG. Tubercles angled to top. 



H. Spines very unequal, some much elongated. 



Spines whitish 12. N. phynmtothele 



Spines horn-colored, reddish or black. 

 No definite central spine. 



Spines horn-colored, short, curved 13. N. magnimamma 



Spines reddish, long 14. A'', macracantha 



Central spines definite. 



Central spines 2 15. A'', johnstonii 



Central spines solitar}-. 



Central spine 2 to 3 cm. long 16. A'', nielanocentra 



Central spine i cm. long; oblong 17. N. nmyonii 



HH. Spines nearly equal, at least none much elongated. 

 Flowers red to pinkish. 



Outer perianth-segments ciliate 18. A^. sarlorii 



Outer perianth-segments not ciliate (so far as known) . 

 Central spines none. 



Spines pinkish with black tips 19. A', seilziana 



Spines straw-colored throughout 20. A^ ortegae 



Central spines i or more. 



Central spines solitary'; radial spines nearlj- equal 21. A', meiacantha 

 Central spines 2 ; some of radials verj' short. . . . 22. N. scrippsiana 

 Flowers yellowish. 



Central spines 4 to 6 23. A^. gisatitea 



Central spines usually wanting 24. A', peninsularis 



EE. Tubercles very short, sj-mmetric. 

 F. Plants globose or depressed. 



G. Axils of tubercles naked 25 . JV. flavovirens 



GG. Axils of tubercles laniferous. 



Some of spines deciduous 26. N. sempervivi 



None of spines deciduous. 



Central spines present 27. N obsciira 



Central spines wanting 28. N. crocidata 



FF. Stems cylindric or ovoid. 

 Central spines wanting. 



Tubercles nearly terete 29. N. polythele 



Tubercles 4-angled. 



Tubercles pointed; axils very woolly 30. N. car?iea 



Tubercles not pointed ; axils not very woolly 31. N. lloydii 



Central siiines several. 



Radial spines reduced to short bristles 32. A', zuccariniana 



Radial spines more elongated than in last species 33. A^. formosa 



