35 



visible when the leaves fall off, a characteristic circular scar 

 around the bud then showing where the leaf was inserted. 



33. The way in which the young Vernation 



leaves, or leaflets, are folded in the bud, which is called 

 vernation, varies in different species. In some cases the edges of 

 the leaf are rolled in towards the midrib on the upper surface of 

 the leaf when the vernation is involute. In other cases the edges 

 are similarly rolled in towards the midrib on the under surface, 

 the vernation being revolute. In others the leaf is not rolled 

 and the longitudinal halves of the blade, turning on the midrib 

 like a hinge, are placed flat face to face with their upper surfaces 

 in contact, the vernation being conduplicate. In others the leaf 

 is so folded on its longitudinal axis that the under-surface is 

 outside and one edge covers the other, the vernation being 

 convolute. In others the leaf is coiled inward from the apex, 

 the vernation being circinnate. In others the leaf-blades are 

 folded between the nerves, the vernation being plicate. 



For illustrations see Plate IX. 



Finally, in some cases, there is no obvious folding, or 

 rolling, and the young leaves are placed practically flat, or 

 slightly curved, one against another. 



A young leaf in the early stages of its development has its 

 tissues imperfectly developed, and the soft green tissue lying 

 between the nerves is particularly susceptible to injury and 

 is liable to be dried up and destroyed if fully exposed to the, 

 sun and air. 



Some protection is therefore commonly provided for it, 

 sometimes by the folding of the lamina, sometimes by the 

 position assumed by the young leaves, and sometimes by 

 protective coverings of hair, wax, gum, or resin. 



Thus in Viburnum cotinifolium we find the young leaves 

 erect on the stem, each pair of opposite leaves having their 

 upper surfaces placed close together, while only the under 

 surfaces are exposed to the light and air. 



The upper surface of each leaf is concave, the under 

 surface convex, and the lamina is plicately folded, the delicate 

 green tissue being thrown into deep folds between the nerves, 

 these folds projecting into the concavity of the upper surface. 

 Thus the green tissue is effectively protected during its early 

 development by the close-set framework of nerves which alone 

 are exposed on the exterior of the young leaves. As the young 

 leaves are thus erect and closely adpressed, we find that tfce 

 upper surface of the petioles is grooved, room biding thus 

 provided for the terminal bud between the opposite leaves. 



2D 



