CHAP. 1.] CACTACEJE. 369 



which are disposed in a spiral manner; and 

 each of which is crowned with a little tuft of 

 radiating spines mixed with down. The flowers 

 are w^ithout stalks, and they are disposed in a 

 kind of zone round the plant. The Melon 

 Thistle or Turk's- cap (Melocactus communis) 

 has a globose stem with deep furrows, the pro- 

 jecting ribs having tubercles bearing tufts of 

 spines. The stem is crowned with a woolly 

 head, from which the flowers are protruded, 

 the flowers themselves resembling those of 

 Mammillaria, but being larger. The Hedgehog 

 Thistles {Echinocactus) have stems resembling 

 those of the different species of Melocactus, 

 but they have not the w^oolly head ; and the 

 flowers rise from the fascicles or tufts of spines 

 on the projecting ribs. The Torch-Thistle 

 (Cereus) has generally an angular stem with 

 a woody axis, and it has tufts of spines on the 

 projecting angles. It has not a woolly head, 

 and the flowers, which are very large and 

 showy, either arise from the tufts of spines, or 

 from indentations in the angles. The limits of 

 this genus are very uncertain ; and several 

 plants which are included in it by some botanists, 

 are placed in other genera by others. The Old- 

 man Cactus was once called Cereus senilis, but 

 it is found to have a woolly head of great 

 size, which has very much the appearance of 



