86 YOUNG AND OLD LEAVES. 



wide strip in the middle of the leaf, remains flat, 

 but the margins are rolled up, sometimes on the 

 upper, sometimes on the under side. The side on 

 which the stomata are most numerous and the 

 green, transpiring tissue is pierced with air-pas- 

 sages, is always concave. In the Crocus the two 

 margins are rolled outwards and united by a broad, 

 white, flat stripe, and in the Star-of-Bethlehem 

 (Ornithogalum), whose leaves are marked with a 

 similar white stripe, the halves are rolled inwards. 

 In the Crocus the stomata are on the under side, 

 in the Star-of-Bethlehem on the upper side of the 

 leaf. The young leaves of Ferns are also rolled 

 together, but the midrib, instead of being flat, is 

 rolled inward spirally, like a watch spring, so that 

 the green segments, springing from either side of 

 the midrib, are packed closely one upon the other. 

 Less common than leaves which are rolled are 

 those which are crumpled in the bud. Here the 

 netted veins make a firm trellis work, or grating, 

 in the meshes of which the green tissue of the 

 leaf appears as if blistered, and the whole leaf 

 has the effect of a crumpled cloth. This is called 

 corrugate or crumpled vernation. Especially strik- 

 ing in this respect are the young leaves of many 

 species of Dock (Rumex), Rhubarb (Rheum), and 



