LETTER XXX. 



THE CACTUS TRIBE THE GOURD TRIBE. 



Plate XXX. 



Besides the plants spoken of in my last letter, 

 there are several others whose placentation is also 

 parietal (see page 39.)? and it will be better, before we 

 proceed to other subjects, to examine some of them ; 

 especially two which are of very common occurrence. 



The plants called Cactuses, which, from the profu- 

 sion of large richly-coloured flowers that some species 

 are loaded with, have given to our conservatories an 

 air of magnificence which was quite unknown till of 

 late years, constitute the small group of Cactacese. The 

 species are in all cases succulent, and with the single 

 exception of the Pereskias, destitute of leaves, in 

 whose room the stem is either green and leaf-like, or 

 at least covered over with a green integument, which 

 has the structure of the pulpy part of a leaf, and like 

 it executes the oifice of respiration. You will form a 

 general idea of this highly curious natural order 

 when you are told that the plants called Indian Figs 

 (Opuntia), with their prickly, jointed, flattened stems, 

 on which the Cochineal insect feeds ; Torch-thistles 

 (various species of Cereus), whose angular trunks rise 

 erect and singly into the air, like fantastic vegetable 



