TOLIAGE leaves: FUNCTION, STRUCTURE, ETC. 47 



38, 39, 40, 190, 191, 192, 193). 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. 40. A globular cactus, showing the rihbed stem, the strong spines, and the entire 

 absence of leaves. 



194). 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 



