96 Water 



tation, but from the bodies of animals, drying the skins 

 of human beings, as the hot, dry air of the desert dries 

 them, though in less degree. 



Since three-fourths of the weight of most plants, and 

 more of many, is made up of water, the air would be 

 always sucking at them, if not prevented. As things 

 are, however, though some, generally very small, 

 amount of water is sucked by the air from the whole 

 surface of a plant, as we have said, its escape is con- 

 fined, as far as may be, in most cases, and especially in 

 dry climates, to the legitimate openings, the pores 

 made for this purpose. 



Soft, thin leaves lose water by evaporation from the 

 whole surface, and have a large number of pores as 

 well, but they grow in situations where they can 

 easily make up the loss. All leaves, however, have 

 some protection more or less in the skin which 

 covers them, this skin being, moreover, as we have 

 said, impregnated with wax, which, though com- 

 monly invisible, often appears as a shiny coating, or 

 as 'bloom.' 



A cabbage, for instance, has a mealy look about it, 

 as if it had been dusted with flour ; many grasses, 

 acacias, and the now well-known Australian gum-tree 

 or eucalyptus, have a similar appearance, and when 

 this 'bloom' is examined it is found to consist of 

 minute rods, or needles, of wax. The substance forms 

 a regular incrustation on the stem of the Peruvian 

 wax palm, whose native land is one of the most rain- 

 less regions of the earth ; and there is nothing more 

 effectual than wax for excluding air and preventing 

 evaporation. Honey stored in wax-cells is, as it were, 

 hermetically sealed up and preserved. 



