MANUAI< 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 tlie 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 th6 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 us to believe more strongly 

 than before that the inner portion of the leaf must 



