MANUAL OF NATURE STUDY. 
81 
FOURTH YEAR. 
1. Rapid review of third year's work . 
2. Uses of leaves, roots , and sap. 
Leaves . See lessons for third grade, reviewing 
form, margin, variation, surface, etc., and proceed 
to the structure of the leaf. Very carefully strip off 
the thin outer covering of any fresh, plump leaf and 
notice its transparency. Have the pupils do the 
same with their leaves. Compare with outer skin 
on fresh, ripe grape; with outer skin of a very ripe 
apple; with the epidermis of our own skin, and 
draw the conclusion that the epidermis of the 
leaf is used for the protection of the inner part. 
Then the inner portion must be very important to 
the life of the plant, otherwise it would not need 
protection. 
The epidermis of our own skin, we said in the 
work for the third grade, has thousands of pores 
through which perspiration may pass to the 
surface and escape. Examine the epidermis of the 
leaf and see whether it is constructed in the same 
way. It will be necessary to use a good hand lens 
for this examination. The larger openings called 
stomata are found on both sides of the leaf, 
but most numerous below in higher land plants. 
This discovery leads ns to believe more strongly 
than before that the inner portion of the leaf must 
