The Inner Structure of the Plantlet. 47 
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). The ob- 
ject of the cuticle is to restrict evaporation (75). To still 
further protect the parts, a layer of wax is sometimes se- 
creted upon the outside of the cuticle, as in the fruit of 
many varieties of the plum and grape, where it is called 
bloom. 
Root-hairs (101) and the hairs and bristles on the stems 
and leaves of many plants are cells of the epidermis that 
are elongated outward. The epidermis must not be con- 
founded with the bark. It is replaced by bark in the older 
stems of woody perennial plants. 
To give further strength and firmness to the upper sur- 
face of the leaf, the first two or three tiers of cells beneath 
the epidermis on the upper side are usually placed endwise, 
(palisade cells) (Figs. 15, 13 and 3). The hardier varieties 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. 15), with those of Fig. 3, which shows a section from a 
leaf of a tender variety of apple. 
66. Stomata (stom’-a-ta). Minute openings through 
the epidermis, connecting open spaces between the interior 
cells (intercellular spaces) with the external air, occur in the 
leaves and young stems of land plants. These openings 
are bounded by a pair of crescent-shaped guard-cells called 
stomata, (singular, stoma, (sto’-ma)) (Figs. 16 and 17 St). They 
are chiefly found on the lower side of leaves, and are ex- 
tremely numerous, but are too small to be seen without the 
microscope. An average apple leaf has been computed to 
