42 THE VITAL FUNCTIONS. 



the injurious effects of moisture ; and 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 Ceroxylon, and 

 the Iriartca have a thick coating of wax, covering 

 the whole of their stems. Sometimes the plant is 

 strewed over witli a bluish powder, possessing the 

 same property of repelling water : the leaves of the 

 Mcsembrymithenium , or Fig-marigold, of the Atri- 

 plex, or Orache, and of the Brassica, or Cabbage, 

 maybe given as examples 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 

 plumage 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 Batracliospermum, are, in like 

 manner, protected by a viscid layer, which renders 

 the leaves slippery to the touch, and which is im- 

 permeable to water. 



Several tribes of plants contain opaque liquids, 

 having a white milky appearance ; this is the case 

 v.ith the Poppy, the Fig-tree, the Coiivohulus, and 

 a multitude of other genera ; and a similar kind of 

 juice, but of a yellow colour, is met with in the 

 Chelulonium, or Celandine. All these juices are of 

 a resinous nature, usually hiu:lily acrid, and some- 

 times even poisonous in their qualities; and their 

 opacity is occasioned by the presence of a great 

 number of minute globules, visible with the micro- 

 scope. The vessels in which these fluids are con- 

 tained are of a peculiar kind, and exhibit ramifi- 

 cations and junctions, resembling those of the blood 



