164 PRACTICAL COimSP: IN BOTANY 



IV. ANATOMY OF THE LEAF 



Material. — For study of the epidermis, leaves of the white garden 

 lily {Lilium album) are best, as the stomata can be seen on their lower 

 surface with the naked eye. Wandering Jew, Spanish bayonet {Yucca 

 aloifolia), anemone, narcissus, iris, canna, show them under a hand lens, 

 but less distinctly. For sections, beet, mustard, and beech leaves may 

 be used, or ready-mounted specimens obtained of a dealer. 



A compound microscope is needed for a minute study of the loaf 

 structure. 



i8i. Stomata. — It was shown in Exp. 64 that the water 

 of transpiration escapes most rapidly, as a general thing, from 

 the under surface of leaves. To find out why this is so, a 

 careful study of the epidermis will be necessary. For this 

 purpose procure, if possible, the leaf of a white garden lily 

 {Lilium album), wandering Jew, Spanish bayonet {Yucca 

 aloifolia), anemone, narcissus, iris, or canna. The first- 

 named is preferable, as the transpiration 

 pores can be seen on it with the naked eye. 

 Examine the under surface with a hand 

 lens, and you will see that it is covered with 

 small eye-shaped dots like those shown in 

 Figs. 218 and 219. Strip off a portion of 



Figs. 218, 219. — , . , • , , , • ^ t ^ 



Stomata of white lUy the cpidei'mis, hold it up to the light on a 

 leaf: 218, closed; 219, pjepg Qf moisteued glass, and they can be 



open. {After Gray.) ^ . 



seen quite clearly with a lens. These dots 

 are the pores through which the water vapor escapes in 

 transpiration, and through which air finds its way into the 

 tissues of the leaf. They are called stomata (sing., stoma), 

 from a Greek word meaning " a mouth." Look for stomata 

 on the upper epidermis ; do you find any, and if so, are there 

 as many as on the under surface ? Do you see any relation 

 between this fact and the results obtained from Exp. 64? 

 Can you see any good reasons why the stomata should be 

 placed on the under side in preference to the upper ? Are they 

 as much exposed to excessive light and heat, or as liable to 

 be choked by dust, rain, and dew here as on the upper side ? 



