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PLAXT PHYSIOLOGY AXD ECOLOGY 



plants merely as a temporary compensation. Water loss takes 

 place more rapidly, as a rule, from the sm-face bearing the larger 

 number of stomata. In consequence, the edges are usually rolled 

 up with the lower side inward, chiefly by reason of the greater 

 turgidity of the upper. The furrowed leaves of monocotyledons, 

 especially the grasses, are well adapted to changes of this nature. 

 The leaves of many grasses and heath plants are permanently 



Fig. 44. Sun and shade forms of Wagnera steUata. The leaves of the sun 

 form are folded or rolled together, while the shade leaves are flat. 



rolled or folded. In these the protection against drouth is very 

 effective. It arises not only from the reduction of surface, but 

 also from the fact that the stomata lie in a chamber that is perma- 

 nently and more or less completely closed. Many mosses roll and 

 twist their leaves when threatened by drouth, but in these the 

 rolling merely reduces the leaf surface exposed. 



167. Reduction of leaf or stem. Plants reduce their surface, 

 and thereby the amount of transpiration, by decreasing the number 



