THE BOG. 157 



must have been brought, at some considerable ex- 

 pense, from a great distance, as it does not grow 

 in the vicinity of London. Rushes* are now 

 used for making mats and brooms ; and the pith, 

 strengthened by a narrow strip of rind, proves an 

 excellent wick for candles which are required to 

 burn for a long time without consuming much 

 tallow, or giving much light. The rushes used 

 for the bottoms of chairs belong to an entirely 

 different tribe of plants, growing also in marshy 

 places, and called Bulrushes or Clubrushes.^ The 

 flower of the Rush is inconspicuous, but not alto- 

 gether unworthy of notice. It approaches very 

 closely in its structure to the beautiful Lily tribe ; 

 the principal difference being that it has dry and 

 rigid petals, or calyx leaves, the number and ar- 

 rangement of which is the same in both. 



Contrary to what we might expect, aquatic 

 plants, however thick the substance of their stems 

 and leaves may appear, are remarkable for the 

 quantity of air contained in their cells, and not 

 for any exuberance of moisture. We can easily 

 see the reason of this, when we recollect, that as 

 they grow either in the immediate vicinity of 

 water, or actually in water, they do not stand in 

 need of reservoirs of juices. They are more liable 

 to sudden floods than excessive droughts ; they 

 are therefore abundantly supplied with cells filled 

 with air, which keep them buoyant, however high 

 the water may rise. On the contrary, plants 

 which thrive in very dry situations have a ready 

 power of absorbing moisture from the atmosphere, 

 which they also eagerly retain. The Cactus tribe 



* Juncus. t Scirpus. 



