30 THE VEGETATIVE FUNCTIONS OF PLANTS 



Leaves may be so altered as to cease to be foliage leaves, 

 and serve, for example, as bud-scales (Fig. 19), or other 

 organs. In some bud-scales both petiole and blade may 

 be wanting, the leaf-base alone serving as the scale (Fig, 

 20). Again, the bud-scale may consist chiefly of petiole. 



FIG. 22. Various types of leaf -blade. 



or of blade, or (as in the tulip-tree) of stipules only (Fig. 

 21). Variations of leaves are illustrated in Fig. 22. 



It is not essential here to endeavor to frame a definition 

 of a leaf, though this would be a profitable exercise for 

 the reader. The main thing is to emphasize the fact that 

 the leaf is an exceedingly plastic organ, that is, appearing 



