CHAPTEE XI. 



Leaves of Peculiar Forms and Uses. 



127. Leaves in Hot, Dry Climates. — In regions -wliere the 

 greatest dangers to vegetation arise from long droughts and 

 the excessive heat of the sun, the leaves of plants usually 

 offer much less surface to the sun and air than is the case in 

 temperate climates. Sometimes the blade disappears and the 



Fig. 88.- 



-Leaf of Nightshade,! with Midrib 

 Prickly above and below. 



Fig. 89. — Spiny Leaves of 

 Barberry. 



expanded petiole answers the purpose of a blade, or again, 

 the leaves disappear altogether, as in the cactuses (Fig. 38) 

 and the green outer layers of the stem do the work of the 

 leaves. 



Sniaimm. 



