FOLIAGE LEAVES: FUNCTION, STRUCTURE, ETC. 47 



38, 39, 40, 185, 186, 187, 188). In the same regions the 

 agaves and yuccas retain their leaves, but they become so 

 thick that they serve as water reservoirs (see Figs. 38, 39, 



FIG. 49. A globular cactus, showing the ribbed stem, tlie strong spines, and the entire 

 absence of leaves. 



189). In all these cases this reduced surface is supple- 

 mented by palisade tissue, very thick epidermal walls, and 

 an abundant cuticle. 



37. Rosette arrangement. The rosette arrangement of 

 leaves is a very common method of protection used by 



