The Inner Structures of the Plantlet. 49 



entire surface of the leaves, stem and root, called the 

 epidermis (Fig. 17 Ep.). This skin is formed of com- 

 paratively thick-walled cells and serves to protect the 

 more delicate parts within. It may be readily with- 

 drawn in some plants, as from the leaves of the live- 

 forever* and echeveriaf and young stems of the plum. 

 The exposed surface ' of the epidermis of the leaves, 

 fruit and young stems of many plants is transformed 

 into a layer that is more or less impervious to water, 

 called the cuticle (cu'-ti-cle), which serves to restrict 

 evaporation (74). To further protect the parts, a 

 layer of wax (bloom) is sometimes secreted upon the 

 outside of the cuticle, as in the fruit of many varieties 

 of the plum and grape. 



Root hairs (100) and the hairs and bristles on the 

 stems and leaves of many plants are cells of the epi- 

 dermis elongated outward. The epidermis must not be 

 confounded with the bark. It is replaced by bark in 

 the older stems of woody perennial plants. 



To give further strength to the upper surface of the 

 leaf, the first two or three tiers of cells beneath the epi- 

 dermis on the upper side are usually placed endwise, 

 (palisade cells, Figs. 17, 15 and 3). The hardier varie- 

 ties of apple, as the Oldenburgh (Duchess), have more 

 numerous and more crowded palisade cells than less 

 hardy varieties. Compare the palisade cells of a leaf 

 of the Oldenburgh apple (Fig. 17), with those of Fig. 

 3, which shows a section from a leaf of a tender variety 

 of apple. 



* Sedum telepMum. f Cotyledon. 



