124 GLASS-HOUSES 



departure from normal structure which is to be seen among 

 the flowering plants. The majority come from the hot desert 

 regions of the New World : their leaves are reduced to sharp 

 dry spines of defence, and their green stems often look like 

 fleshy leaves, but are more watertight than ordinary leaves. 



The Opuntias or Nopals yield Prickly Pears, much eaten 

 in S. Italy and in warm countries under the name of Fiche 

 d'lndia^ and their stems are used for making most effective 

 fences. The Opuntia cocdnellifer or Nopal is largely culti- 

 vated as the food-plant of a parasite, the cochineal insect^ 

 the wingless females of which have the power of making from 

 the Nopal the well-known scarlet dye. ,500,000 worth of 

 cochineal has been annually exported from Mexico alone, 

 but most of the British import comes from Teneriffe. 



Echinocactus resembles a Melon, bristling all over with thorns, 

 which are used in Mexico as toothpicks (E. visnaga ; visnaga = 

 toothpick). E. cylindraceus has long curved spines. 



Cereus develops some of the most splendid, although in 

 general the most short-lived of flowers. C. grandiflorus, the 

 Night-blowing Cereus, when in the Garden, put forth, now and 

 then in the close of evening, one or more blooms of great 

 beauty, whose fragrance was sufficient to fill the whole house 

 with a delicate perfume of vanilla, but by the morning it was 

 closed and faded. Unfortunately the house is only open to 

 the public for two hours in the afternoon. 



Of Pilocereus senilis^ the Old Man Cactus, with leaves 

 represented by white wool like an old man's hair, the Garden 

 possessed a venerable specimen said to have been several 

 hundred years old, but it died shortly after No. 12 Green- 

 house had been heightened for him. His shrivelled skin in 

 the museum is 15 ft. long. There are large plants in Mexico 

 which, from the slowness of their growth, may be as much 

 as a thousand years old. C. giganteus attains to a height 

 of 50 ft. 



