170 
HAIRY LEAVES 
OTICE always whether a leaf is smooth or hairy. 
Do you remember the mullein that sends up 
its tall spires over the hill pasture? The grayish 
leaves of this mullein are so hairy that they feel 
almost like wool. What is the use of all this hair? 
It is not likely that a plant would wrap itself in this 
hairy coat except for some good reason. 
It is believed that this coating of the mullein pre- 
vents animals from eating the leaves, and so destroy- 
ing the plant. In the mouth, these hairs slip from 
the leaf blade, and cause a most unpleasant sensation. 
But usually the hairs on a leaf are helpful because 
they prevent too much perspiration or giving-off of 
water. The more freely the hot sun beats upon a 
leaf, the more quickly the water is drawn away from 
it. You can see just how this is by hanging a wet 
towel_in front of the fire. - In a very short: timestie 
heat from the burning coals draws the water from 
the towel... But put a screen. between the’ diretamm 
the towel, and the water passes off more slowly. 
Now, the hairs on that side of the leaf which faces 
the sun act as a screen from its fierce heat. We have 
learned how important it is that the leaf should not 
part with its water more quickly than the roots can 
make up the loss. We know that when a leaf does 
this, it wilts just as a leaf wilts when it is picked and 
cut off from its water supply, on account of the col- 
lapse of the walls of the many little cells which are 
emptied of water. 
