48 THE VITAL FUNCTIONS. 



for a similar purpose we find the surface of many 

 plants covered with a varnish of wax, which is 

 another secretion belonging to the same class : thus 

 the CeroxyloHy and the Iriartea have a thick 

 coating of wax, covering the whole of their stems. 

 Sometimes the plant is strewed over with a bluish 

 powder, possessing the same property of repelling 

 water : the leaves of the Mesembryanthemum, or 

 Fig-marigold, of the At?iplex, or Orache, and of 

 the Brassica, or Cabbage, may be given as ex- 

 amples of this curious provision. Such plants, 

 if completely immersed in water, may be taken 

 out without being wetted in the slightest degree ; 

 thus presenting us with an analogy to the plu- 

 mage of the cygnet, and other aquatic birds, 

 which are rendered completely water-proof by 

 an oily secretion spread over their surface. 

 Many aquatic plants, as the Satrachosjjennuin^ 

 are, in like manner, protected by a viscid layer, 

 which renders the leaves slippery to the feel, and 

 which is impermeable to water. 



Several tribes of plants contain liquids that 

 are opaque, and of a white milky appearance ; 

 this is the case with the Poppy ^ the Fig-tree, the 

 Convolvulus, and a multitude of other genera ; 

 and a similar kind of juice, but of a yellow 

 colour, is met with in the Chelidonium, or Celan- 

 dine. All these juices are of a resinous nature, 

 and usually highly acrid, and even poisonous in 

 their qualities; and their opacity is occasioned 



