FOLIAGE LEAVES: FUNCTION, STRUCTURE, ETC. 47 



38, 39, 40, 185, ISO, isr, 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, 



t_-i ■ - 



Fig. 40. A globular cactus, showing the ribbed stem, the strong spines, and the entire 

 absence of leaves. 



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

 mented by palisade tissue, very tliick epidei-mal walls, and 

 an abundant cutiele. 



37. Rosette arrangement. — The rusette arrangement of 

 leaves is a very common method of protection used by 



