86 PB ACTIO AL BOTANY. 



165. The place of every leaf on every plant is already 

 fixed in the hud by unerring mathematical rule. 



The mode, in which leaves are disposed iii the bud, is 

 usually called veenation. But the term also denotes the 

 manner in which the leaf itself is folded, coiled, or packed 

 up in the bud. Some botanists therefore use the term prm- 

 foliation, to denote the arrangement of the leaves in re- 

 spect to one another, while by vernation they understand 

 the manner in which the leaf itself is folded. 



The leaf, considered in itself, is sometimes straight, flat, 

 and open in the bud, but oftener bent, folded, or rolled. 

 It is said to be inflexed, or reclined in vernation, when its 

 upper part is bent down upon the lower, as the young 

 blade of Liriodendron is bent upon the petiole ; con- 

 dwplicate, when folded by the midrib, with the lateral 

 halves brought together, face to face, as in the Magnolia, 

 the Cherry, the Oak ; plicate, or plaited, when folded like 

 a fan, as in Maple, Currant, Vine, Bii-ch. "When the leaf 

 is rolled, it is so in one of four modes. It is circvnnate, 

 when it is rolled downward from the tip, as in Sundew ; 

 convolute, when rolled up parallel with the axis from one 

 of its sides, as in the Plum ; involute, when it has both 

 margins rolled inward, as in Water-Lily, Apple, and 

 Violet ; revolute, when it has both edges rolled outward, 

 as in Azalea and Salix. 



The arrangement of leaves in the bud with respect to 

 one another, or prasfoliation, is in descriptive botany 

 briefly distinguished as valvate and imhricate. The val- 

 vate arrangement, in which the edges of the leaves meet 

 with each other, is more common in plants with opposite 

 leaves. In imbricate prtefoliation the outer leaves succes- 

 sively overlap the inner, at least by their edges. 



Cross-sections of buds show us, as it were, an epitome 



