314 NATURE-STUDY 



answers. Though we may find pleasure in the beauty of 

 the fohage and enjoy its shade, this is not the reason why 

 plants have leaves. 



A plant breathes, perspires, makes its food, and also does 

 other useful things with its leaves. Looked at in this way a 

 leaf is a very important organ to a plant. 



While the full meaning of a leaf cannot be made clear to 

 grade pupils, yet its general function can be taught them by a 

 few experiments. 



Plants wilt because they lose water from their leaves. 

 This is called transpiration. It may be very easily shown 

 by cutting from a geranium or other plant some leaves, 

 covering the cut end with vaseline or wax so as to prevent 

 the escape of moisture through these entjs, and placing the 

 leaves under a tumbler in the sunlight or other warm place. 

 In a short time drops of moisture given off by the leaf will 

 be collecting on the inside of the glass. 



This water must come out of the leaf elsewhere than from 

 the cut ends. It is exhaled as vapor from minute openings, 

 called breathing pores, in the skin or epidermis of the leaf. 

 These pores are visible readily under a compound micro- 

 scope; and on the leaves of the Wandering Jew they are 

 visible with a simple magnifying glass. On the common 

 liverwort, marchantia, though not a leafy plant, the breath- 

 ing pores are visible easily to the unaided eye. If speci- 

 mens like these can be got, the pores should be shown. 

 At any rate, diagrams should be made giving a leaf in 

 cross section, to show the loose, spongy tissue of green 

 cells within the leaf, the conducting strands (veins), and 

 the breathing pores. Show also surface views of the 

 pores. Through these pores the moisture escapes, and when 



