164 PRACTICAL COURSE IN BOTANY 
Iv. ANATOMY OF THE LEAF 
Marertau. — 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 leaf 
structure. 
181. 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 
Fies. 218, 219. — : : ; : 
Secreta ite lly the epidermis, hold it up to the light on a 
leaf: 218, closed; 219, 
open. (After Gray.) Piece of moistened glass, and they can be 
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? 
