206 ELEMENTS OF BOTANY. 
stomata from becoming clogged with water, and the hairy net- 
work on the under side of the leaf (into which they often 
open) may sometimes serve to prevent them from becoming 
clogged with dust, and certainly often hinders too rapid 
transpiration. 
In regions where there is a long rainless season, many 
plants produce bulbs in which their nourishment, acquired 
Fie. 185.— Arctic Willow. The greater part of a pistillate plant, about 
natural size. 
during the growing season, is buried until the next rainy 
period comes round. 
Desert plants are commonly fleshy and often leafless, in 
the latter case offering to the dry, scorching air only a small 
surface of green bark through which transpiration and 
