MINUTE ANATOMY OF FLOU'KRING PLANTS '221 



rather close together, leaving scanty vacant spaces ; those 

 of the lower are commoul}' irreguhrr in shape, most of them 

 with their long diameter parallel to the face of the leaf, 

 and are very loosely arranged, leaving many and wide air 

 chambers. The a'reen color of the lower is therefore 



381. Magnified section of a leaf of White f-ily, to exliiljit (lie eclliiiiir slvuc- 

 ture, both of upper and lowcv stratum, the air passages of the lo\ver. 

 and the epidermis in section; also a little of the lower face, ivitli 

 some of its stomates. 



diluted, and paler than that of the U|)per face of the leaf. 

 The upper part of the leaf is so constructed as to bear the 

 direct action of the sunshine ; the lower so as to afford 

 freer circulation of air, and to facilitate the escape of mois- 

 ture. It communicates more freely than tlie upper with 

 the external air by means of pores in the epiidermis. 



526. The upper cylindrical cells are known as the puli- 

 sade cells. The lower, irregular, or sometimes slightly 

 In-anching cells make up the spongy parenchyma, so called. 



527. The epidermis is usually composed of a single layer 

 of more or less flattened cells, devoid of chlorophyll, and 

 mostly of irregular outline (Figs. 382, 383). 



The walls of the epidermis are commonly thickened 

 externally bj' the addition of a layer of a waterproof sub- 

 stance. This layer is easily distinguished in the cross 

 section from the original exterior walls of the cells. It 

 is termed the cuticle. The several walls of each epider- 

 mal cell are impregnated with the same waxy or fatty 



