STANDLEY TREES AND SHRUBS OF MEXICO. 979 



Spines all very much alike. 



Perianth segments obtuse 79. N, denudata. 



Feranth segments pointed. 



Flowers about 7 mm. long 80. N. lenta. 



Flowers about 20 mm. long 81. N. Candida. 



Spines unlilie, the centrals unlike the others 82. N. vetula. 



Spines 20 or fewer. 

 Plants globose. 



Flowers red 83. N. fertilis. 



Flowers white. 



Central spines solitary ; radials 7 to 9 84. N. decipiens. 



Central spines 5 to 8 ; radials 16 to 20 85. N. discolor. 



Plants cylindric. 

 Joints very fragile, breaking loose when touched or jarred. 



86, N. frag'ilis. 

 Joints not fragile. 



Spines all radial and recurved 87. N. elongata. 



Spines both radial and central. 

 Axils of tubercles not bristlj'. 



Spines all yellow 88. N. ecMnaria. 



Spines not yellow. 

 Upper central spines more or less conniveut over the 



top of plant 89. N. pottsii. 



Upper central spines not connivent over the top of 



plant 90. N. mazatlanensis. 



Axils of tubercles bristly. 



Stems slender-cylindric or globose ; species of central 



Mexico 91. N. sphacelata. 



Stems short-cylindric or globose ; species of Baja Cali- 

 fornia. 

 Spines nearly white or at least becoming so ; seeds 

 minute. 

 Spines all white or nearly so ; spine areoles at first 



lanate 92. N. albicans. 



Spines tan-colored with dark tips ; spine areoles not 



lanate 93. N. slevinii. 



Spines not white ; seeds 3 mm. long 94. N. palmeri. 



AA. Plants with some of the central spines hooked. 

 Tubercles milky ; seeds brown. 



Plants globose 95. N. uncinata. 



Plants cylindric 96. N. hamata. 



Tubercles never milky; seeds black (except in Nos. 97 and 98). 

 Seeds brown. 



Fruit red; flowers from side of plant 97. N. rekoi. 



Fruit green ; flowers from near base of plant 98. N. solisii. 



Seeds black. 



Fruit depressed, long-persisting 131. N. longiflora. 



Fruit elongate, clavate, ripening quickly. 



Seeds rugose 130. N. nelsonii. 



Seeds not rugose. 

 F. Plants usually small ; spines setaceous to delicately acicular. 



