u 



PLANT RELATIONS. 



Fig. 3G. A branching hair from the leaf of common mullein. The whole plant has a 

 felt-like covering composed of such hairs. 



it 



comparatively thick, although they may he very numerous 

 (see Figs. 4, 172). In this way each leaf exposes a small 



surface to the dry- 



v/ ;\ :^\. ^j m g aii" and intense 



-"V; '.i**, ? * ..-;/' ; sunlight. In our 



..• hU'jf^l'''- southwestern dry 



regions the cactus 

 abounds, plants 

 which have reduced 

 their leaves so much 

 that they are no 

 longer used for 

 chlorophyll work, 

 and are not usually 

 recognized as leaves. 

 In their stead the 

 globular or cylin- 

 1 >"•' drical or flattened 



stems are green and 



Fig. 37. A scale from the leaf of Shepherdia. These 



6cales overlap and form a complete covering. do leat WOI*K (.TlgS. 



: mm 



<i*lP 



