THE SUB-TROPICAL ZONE. 145 



tribe is that generally known as the cactus, of 

 which there are eight hundred species, not one 

 of which is known as a native of either Europe, 

 Asia, Africa, or Australia, though in many of 

 these they have been introduced, and grow 

 freely as naturalized plants, as for, instance, on 

 Mount ./Etna. One of the most splendid is the 

 night-blowing cereus, (Cereus grandiflorus,) the 

 blossoms of which begin to expand about six 

 or seven in the evening, and are fully blown by 

 eleven o'clock, but by three or four in the 

 morning they fade, and hang down quite de- 

 cayed. There is scarcely a flower known of 

 greater beauty than this. Its blossoms are 

 neaily a foot in diameter ; the outer petals are 

 of a dark brown, the inner ones of a splendid 

 yellow, which gradually shades off to the most 

 brilliant white in the centre of the flower. 

 When several of these magnificent flowers, 

 therefore, are open at once upon a single plant, 

 they seem like stars shining out in all their 

 lustre, verifying the poet's declaration 



" Darkness shows us worlds of light, 

 We never see by day." 



Some of the species, forming the genus Melocactus 

 are globular, furrowed and beset with spines, 

 and in shape greatly resembling melons. 



Another, Cereus semlis, is called the old man 

 cactus ; it is of an oblong shape, about three 

 inches high, of a greyish colour, and covered 

 with long hair-like bristles, like the grey head 

 of an old man. It has a very singular appear- 

 ance. The creeping cereus, (or " creap in 

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