149 
such a damp cloud as is made by the moist palms of 
your warm hands. 
When water passes from your hands, you say that 
you are perspiring; and when water passes away from 
the plant, we can say that the plant perspires. Some 
plants perspire more freely than others. A sunflower 
plant has been known to give off more than three 
tumblers of water a day by this act of perspiration. 
There is a tree, called the Eucalyptus, whose leaves 
perspire so freely that it is planted in swampy places in 
order to drain away the water. 
Of course, the more quickly the leaves throw off 
water, the faster the fresh supply pushes up the stem. 
If the leaves do their work more quickly than the 
roots make good the loss, then the plant wilts. 
When a leaf is broken from a plant, it soon fades. 
Its water supply being cut off, it has no way of making 
good the loss through the leaf mouths. 
Just as the air in a balloon keeps its walls firm, so the 
water in the leaf_cells keeps the cell walls firm. 
As a balloon collapses if you prick it with a pin, and 
let out the air, so the cell walls collapse when the cells 
lose their water; and when the cell walls of a leaf col- 
lapse, the leaf itself collapses. 
a i ar 
HOW. A PLANT -SFORES, 10S FOOD 
FE see that the water is drawn away from the 
earth broth into the air by the heat of the sun, 
just as water is drawn from the broth we place on the 
