PLANT STUDIES 
FIG. 3G. A branching hair from the leaf of common mullein. The whole plant has a 
felt-like covering composed of such hairs. 
comparatively thick, although they may be very numerous 
(see Figs. 4, 172). In this way each leaf exposes a small 
surface to the dry- 
ing air and intense 
sunlight. In our 
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- 
drical or flattened 
stems are green and 
FIG. 37. A scale from the leaf of Shepherdia. These & 
scales overlap and form a complete covering. do leaf Work (FlgS. 
