i6 



THE LEAF 



the giving off of moisture, just as animals do through the 

 pores of the skin.^ Now, we all know what happens to us 

 if the perspiration glands of our body get stopped up, and 

 hence we need not be surprised if hedgerows can not be 

 'kept vigorous and healthy by dusty roadsides, nor if even 

 sturdy trees and shrubs take on a sickly look when the 

 summer rain delays too long to give them their accus- 

 tomed bath. 



16. Stomata. — The transpiration pores of leaves are 

 called stomata (sing, stoma) from a Greek word meaning 

 "mouths." Generally they are too small to be seen with- 

 out a compound microscope, but their presence can be 

 made manifest by a simple experiment. Place a bit of 

 looking glass against your cheek or your arm on a warm 

 day, and it will soon be covered with a film of moisture 

 from the skin. Next, place the glass in contact with the 

 under side of a healthy growing leaf for thirty to forty-five 

 minutes, and see if you can detect any moisture on it. 

 The deposit will probably be fainter than that from the 

 skin, but the presence of any at all will show that the leaf 



transpires. 



There are a few plants, such as the 



white lily of the gardens {L. caitdidum) 



and the wandering Jew, in which the 



stomata are large enough to be seen 



with ' a hand lens. 



The common iris also 



shows them, though 



not so distinctly. 



Strip off from the 



under side of such a 



leaf a portion of the 

 epidermis, or outer covering. Place it 

 between two bits of glass with the outside uppermost, and 



4. — Portion of the 

 epidermis of the gar- 

 "den balsam, highly 

 magnified, showing the 

 very sinuous walled 

 epidermis cells and 

 three stomata {after 

 Gray). 



5 6 



S, 6. — Stomata of 

 while lily leaf: 5, closed; 

 6, open (Gray). 



^ Transpiration, though similar in external effects to the perspiration of ani- 

 mals, must not be confounded with it, as the two functions are physiologically 

 quite different. 



