LOSS OF WATER 
33 
ing matter, but the smaller cells contain numerous green 
bodies. The green substance is chlorophyll (leaf -green) , 
and the separate green particles are chlorophyll-bodies, or 
chloroplasts. Between each pair of smaller cells is a tiny 
hole or stoma (from a Greek word meaning mouth or 
opening), and the two cells are the guard-cells of the 
stoma (plural, stomata} (Fig. 26). 
The structure of the upper epidermis of the same leaf 
(Fig. 23) is seen to be quite similar to that of the lower, 
FIG. 26. Photomicrograph of stomata from a leaf of Verbena ciliata, 
showing their condition at 9 A.M. (After Lloyd.) 
except that in most plants there are fewer stomata in the 
upper than in the lower epidermis. In some leaves (e.g., 
barberry, osage orange, lilac) there are no stomata in the 
upper epidermis; while in other plants, such as, for ex- 
ample, the water-lily whose leaves float on water, 
there are stomata in the upper epidermis but none in the 
lower. 
36. Microscopic Structure in Cross-section. Since all 
objects examined with the aid of a microscope are observed 
with transmitted light, that is, by light that passes through 
