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 ciltata, 

 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.y 

 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. 



35. Microscopic Structure in Cross-section. — Since all 

 objects examined with the aid of a microscope are observed 

 with transmitted light, that is, by Hght that passes through 



