THE SUB-TROPICAL ZONE. 143 



chief features in the vegetation is formed by the number of 

 succulent plants, of the same nature, and some of them of 

 the same family, as our Houseleek (Sem-pervivum). 



As rain seldom falls in these regions, these succulent 

 plants, which may be called "vegetable camels," are pro- 

 vided with an apparatus of little cavities in their fleshy 

 stems, in which, when the rainy season comes, they lay in a 

 supply of moisture, by which the life of the plant is sup- 

 ported through the long drought ; the outer skin being so 

 thick as to prevent the absorption of this moisture by the 

 hot sun to which they are exposed. 



In Teneriffe the Sempervivums are very common, and 

 often become " shrubs of some size ; growing on steep cliffs 

 and rocks in the neighbourhood of the sea, and on old 

 mansions ; making them glow with the most brilliant golden 

 tints." 



.With our limited English ideas of the Spurge tribe (Eu- 

 pkorbiacetf) , ranging from the little weed we are for ever 

 pulling up in our gardens, to the Box-tree (Buxus), which 

 grows in such a decorous, English sort of way we can 

 scarcely believe, at first sight, in the identity of the Euphor- 

 bias we meet with in the Canary Islands. Till we have 

 seen the blossom we should unhesitatingly say they were 



