CHAPTER III. THE LEAF. 



J 9 



stem. Moreover, they always appear in acropetal order, that 

 is, the older ones are lower down, and, as the stem elongates, 

 younger ones are found higher up on the stem. 



Prefoliation or Vernation. By this is meant the arrange- 

 ment of the leaves in the bud, a matter of considerable import- 

 ance to observe in the study of plants. We may study it from 

 two points of view ; we may consider the individual leaf, how 

 it is folded, bent or rolled, or we may consider how the leaves 

 are arranged with reference to each other. 



Studying the individual leaf, we distinguish the following 

 forms : If the apex is bent inward toward the base, as the leaf 



Fig. 29. 



Fig. 30. 



Fig. 31. 



Fig. 29. — Voting ieaf of the Tulip-tree, illustrating reclinate or infle.xed vernation. 

 Fig. 30. — Voungleaf of Oak, illustrating conduplicate vernation. 



Fig. 31.— Transverse section of a young leaf of the Wild Cherry, illustrating convolute 

 vernation. 



of the Tulip-tree, Fig. 29, it is described as reclinate or inflexed ; 

 if it is doubled inward on the midrib, so that the two sides are 

 applied to each other, face to face, as in the Oak, Fig. 30, it is 

 called cojiduplicate ; when rolled inward from one margin to the 

 other, as in the Wild Cherry, Fig. 31, it is said to be convolute ; 

 when rolled inward from the apex toward the base, as in the 

 Sundew and in Ferns, Fig. 32, it is called circinate ; when, as in 

 the Birch, Fig. ^, it is folded somewhat like the folds of a fan, 

 it is described as plicate ; when, as in the common Violet, Fig. 

 34, it is rolled inward from each margin it is termed involute ; 

 and when, as in Yellow Dock, Fig. 35, it is rolled outward from 

 each margin, it is called revolute. 



