YOUNG AND OLD LEAVES. 87 



some Primroses (Primula). A leaf is often both 

 crumpled and rolled, the crumpled leaves having 

 their margins rolled up in the bud. 



The commonest kind of vernation is folding. 

 In this form the ribs are flat, and only the green 

 tissue between the ribs lies in folds. The manner 

 of folding varies according to the form and dis- 

 tribution of the ribs of the leaf. When the leaf 

 has many radial ribs, like the Lady's Mantle 

 (Alchemilla, Fig. 17 7 ), the leaf is folded in the bud 

 like a fan. The ribs, which in the full-grown leaf 

 diverge like rays, lie side by side, and the tissue, 

 which eventually is stretched out flat, makes deep 

 folds, pressed one upon the other. If each of the 

 ribs makes the midrib of a segment, as in Five- 

 finger (Potentilla) and Oxalis (Fig. 17 8 ), the fold- 

 ing is the same ; each leaflet is folded along the 

 midrib like a sheet of paper, and these folded leaf- 

 lets lie together like the sheets of paper in a box. 



When the leaves are feather-veined and the leaf- 

 lets are opposite each other on a common stalk, 

 like the leaves of Rose and Walnut (Fig. 17 3 ' 4 ), 

 they are folded together along the midrib and laid 

 one upon the other. In the Rose the common stalk 

 is so short in the bud that the leaflets all seem to 

 come from the same point like the Potentilla. In 



