EXPLANATION OF THE FIGURES. 



PLATE IX. 



Fig. i. Diagram of involute vernation. 

 2. revolute 



3. conduplicate vernation. 



,,4. convolute 



,. 5. circinnate 



6. plicate 



(a) (a) throughout is the midrib ; (<$), the upper surface, and (<:), the 



lower surface, or back of the leaf. 



Figs. 7 9. Stages in the development of the leaves of Viburnum colinifolium. 

 The opposite leaves (a) (a), when very young, are erect, and with 

 their upper surfaces in close contact, only the lower surface being 

 exposed to the light and air. The lamina is plicately folded, and the 

 delicate green tissue is protected by the close-set framework of nerves 

 which alone are exposed on the lower surface. As development 

 proceeds the folds of green tissue are flattened out and the leaf is 

 thrown outward and downward, the upper surface being finally 

 exposed to the full rays of the sun as in Fig. 9. 

 The petioles of the young leaves are grooved on their upper surface, 

 so that space is provided for the terminal bud between them. In 

 Fig. 8, (b) represents the terminal bud in cross section, and (c) (c) 

 the closely adpressed petioles also in section. 

 Figs. 7 and 8 slightly enlarged, Fig. 9. X J. 



