20 PART I. — ORGANOGRAPHY. 



It must be borne in mind that in botanical usage the inner 

 surface of the leaf is that which, in the majority of flattened 

 leaves, constitutes the upper surface when fully expanded ; it is 

 also called the ventral surface, and the outer is termed the dorsal. 



Fig. 32. 



Fig. 33. 



Fig. 



Fig. 3s. 



Fig. 32.— Young Fern leaf, illustrating circinate vernation. 



Fig. 33. — Young leaf of the Birch, illustrating plicate vernation. 



Fig. 34. — Transverse section of the young leaf of the common Violet, illustrating 

 involute vernation. 



Fig. 35. — -Transverse section of the young leaf of Yellow Dock, illustrating revolute 

 vernation. 



When considered with reference to each other, several distinct 

 forms of prefoliation are also observed : It is equitant when, as 

 in the Iris, the leaves are conduplicate, and those exterior over- 



Fig. 36. 



Fig. 37. 



Fig. 38. 



Fig. 36. — Diagram illustrating equitant vernation. 



Fig. 37. — Diagram of obvolute or half-equitant vernation. Leaves of Sage. 



Fig. 38. — Diagram of triquetrous vernation. Leaves of Sedge. 



ride or straddle successively both margins of the ones next 

 interior to them, Fig. 36 ; it is called obvolute or half-equitant 

 when, as in the Sage, the leaves are conduplicate, and each 



