WATER AND MARSH PLANTS 



37i 



many with erect strap-shaped leaves, such as Iris, Bur-reed, 

 Flowering Rush, Arrowhead, the Reed Poa or Mead-grass 

 (Glyceria aquatica), and the Common Reed (Phragmites). 

 The last named is a good indicator of the direction of the 

 prevailing winds ; it has smooth leaf -sheaths, and all the 

 upper exposed blades turn round in the direction in which 

 the wind is blowing (Fig. 240). 



Extending farther into the water (d) are the Smooth 

 Horsetail, Water Plantain, and Mare's-tail. Usually these 



Fig. 239. Transect of a Pond. 



avoid complete submersion, their upper parts growing 

 above the surface of the water. They are closely followed 

 by species like Water-Lilies (e), Water Buttercups, Floating 

 Mead-grass (Glyceria fluitans), and some Pond-weeds 

 which, though rooted in the mud, have some leaves in 

 the water, and others (usually of a different type) floating 

 on the surface. 



In the Water Buttercups the submerged leaves are 

 dissected (Fig. 242) ; the floating leaves are entire. Sub- 

 merged leaves of the Water-Lily are large and very thin, 

 while the floating leaves are thick, and covered on the upper 



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