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). 
EK. Tubercles more or less elongated. 
F. Tubercles terete throughout. 
Spines yellow or reddish. 
Spines red... ee ce ee eee eee eens I. 
Spines yellow... 0.0.2... cece cc cee ee teen eee 
Spines usually white except tips, at least not red or yellow. 
Central spines 1 or 2. 
Central spines about length of radials................. 3. 
Central spines much longer than radials............... 4. 
Central spines 4 to 7. 
Outer perianth-segmentsentire;centralspineslong, slender 5 
Outer perianth-segments erose; central spines not elon- 
gated, stouter than in preceding species. 6 
FF. Tubercles more or less angled. 
G. Tubercles nearly terete towards apex. 
Outer perianth-segments and scales more or less fim- 
briate. 
Flowers reddish....... 20... 00. c cece eee e ce eee eee 7. 
Flowers light yellow. ............ 0.0. cee eee eee eee 8. 
Outer perianth-segments and scales entire. 
Radial spines white; flowers pinkish............... .. od. 
Radial spines brownish; flowers white to cream- 
colored. 
Plant hemispheric; radial spines 9 to 13; perianth- 
segments acute..................006- 10. 
Plant much flattened; radial spines 18 or fewer; 
perianth-segments acuminate.......... Il. 
GG. Tubercles angled to top. 
H. Spines very unequal, some much elongated. 
Spines whitish............0..0. 0.0.00. c eee ee eee 12. 
Spines horn-colored, reddish or black. 
No definite central spine. 
Spines horn-colored, short, curved............ 13. 
Spines reddish, long................. 00000005 14. 
Central spines definite. 
Central spines 2........... 0.0... cee ee eee ee 15. 
Central spines solitary. 
Central spine 2 to 3 cm. long.............. 16. 
Central spine 1 cm. long; oblong........... 17. 
HH. Spines nearly equal, at least none much elongated. 
Flowers red to pinkish. 
Outer perianth-segments ciliate................... 18. 
Outer perianth-segments not ciliate (so far as known). 
Central spines none. 
Spines pinkish with black tips............... 19. 
Spines straw-colored throughout.............. 20. 
Central spines 1 or more. 
Central spines solitary; radial spines nearly equal 21. 
Central spines 2; some of radials very short.... 22. 
Flowers yellowish. 
Central spines 4 tO6.......... 0... ccc cece eee ee 23. 
Central spines usually wanting................... 24. 
EE. Tubercles very short, symmetric. 
F. Plants globose or depressed. 
G. Axils of tubercles naked.............0 0.00.00 cee cee eee 25. 
GG. Axils of tubercles laniferous. 
Some of spines deciduous. ...............0 00 c eee eee 26. 
None of spines deciduous. 
Central spines present............. 0.0.0 c cee cee ees 27. 
Central spines wanting............... 0.00000 ee uee 28. 
FF. Stems cylindric or ovoid. 
Central spines wanting. 
Tubercles nearly terete... 0.0.0... cece ec ee eee eee tees 29. 
Tubercles 4-angled. 
Tubercles pointed; axils very woolly.................04. 30. 
Tubercles not pointed; axils not very woolly............. 31. 
Central spines several. 
Radial spines reduced to short bristles..................... 32 
Radial spines more elongated than in last species........... 33 
22 
22 
22 22 
. mammillaris 
. nivosa 
gaumert 
petrophila 
arida 
brandegeet 
. gummifera 
. macdougalit 
N. heydert 
_N. 
2 2% 3 
. hemisphaerica 
. applanata 
. phymatothele 
magnimamma 
. macracantha 
. johnstonii 
. melanocentra 
runyonit 
sartorit 
. settziana 
ortegae 
. metacantha 
. Scrippsiana 
gigantea 
peninsularts 
. flavovirens 
sem pervivt 
obscura 
. crocidata 
polythele 
carnea 
lloydii 
zuccariniana 
formosa 
