86 
MANUAL OP NATURE STUDY. 
Frequently the petiole is grooved upon the upper 
surface so that the surplus water may be carried to 
the stalk, or trunk, and hence down the plant, moist¬ 
ening its entire surface. If the rain continues un¬ 
til the leaves are loaded with water, the petioles 
bend with the weight, the margin and apex of the 
leaf gradually straighten and turn downward, allow¬ 
ing the water to flow as from a roof, dropping from 
leaf to leaf, branch to branch, making its way to 
the very outer edge of the longest limb, from which 
it pours upon that part of the ground immediately 
over the finest roots of the tree; thus the leaves, after 
they themselves are supplied with drink, turn the 
surplus over to the roots, a very clever act 
indeed. 
Summary:— 
Leaves are used (1) for the assimilation of food, 
making plant-substance; (2) for transpiration of 
moisture; (3) for respiration, breathing in carbon 
dioxide and throwing out oxygen; (4) for shade, 
protecting delicate shoots and fruit from heat of sun; 
(5) for sloping off the rain so that it may fall with¬ 
in easy reach of the finer roots of the plant; and 
we may add for shading animals and man from the 
hot sunshine. At least the shade is so utilized for 
such purposes. Also for medicine, and tea to 
drink. 
