LEAVES 223 



the leaves of a plant are so adjusted to one another that they 

 form a mosaic. 



The necessary exposure of leaves to the light involves the' 

 corresponding danger of excessive transpiration. The pro- 

 tective structures against the danger of transpiration are 

 chiefly the epidermis with its cuticle, the palisade layer, and 

 water-storage tissue. The plants further equipped for pro- 

 tection by the position of their leaves are those which have the 

 rosette habit, or profile leaves, or motile leaves. 



While foliage leaves may be regarded as representing the 

 usual leaf, they may be replaced by structures that do not 

 have the appearance, nor, in many cases, the function of foli- 

 age leaves. Such replacing structures are called " modified" 

 leaves chiefly because they appear in the position usually 

 occupied by leaves. 



